Copyright © 1990, 1991, 1992, 1993, 1994, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc. Contributed by Cygnus Solutions. Written by John Gilmore. Second Edition by Stan Shebs.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
This document documents the internals of the GNU debugger, gdb. It includes description of gdb's key algorithms and operations, as well as the mechanisms that adapt gdb to specific hosts and targets.
Before diving into the internals, you should understand the formal requirements and other expectations for gdb. Although some of these may seem obvious, there have been proposals for gdb that have run counter to these requirements.
First of all, gdb is a debugger. It's not designed to be a front panel for embedded systems. It's not a text editor. It's not a shell. It's not a programming environment.
gdb is an interactive tool. Although a batch mode is available, gdb's primary role is to interact with a human programmer.
gdb should be responsive to the user. A programmer hot on the trail of a nasty bug, and operating under a looming deadline, is going to be very impatient of everything, including the response time to debugger commands.
gdb should be relatively permissive, such as for expressions. While the compiler should be picky (or have the option to be made picky), since source code lives for a long time usually, the programmer doing debugging shouldn't be spending time figuring out to mollify the debugger.
gdb will be called upon to deal with really large programs. Executable sizes of 50 to 100 megabytes occur regularly, and we've heard reports of programs approaching 1 gigabyte in size.
gdb should be able to run everywhere. No other debugger is available for even half as many configurations as gdb supports.
The first edition of this document was written by John Gilmore of Cygnus Solutions. The current second edition was written by Stan Shebs of Cygnus Solutions, who continues to update the manual.
Over the years, many others have made additions and changes to this document. This section attempts to record the significant contributors to that effort. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here.
Plea: This section has only been added relatively recently (four years after publication of the second edition). Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
A document such as this relies on being kept up to date by numerous small updates by contributing engineers as they make changes to the code base. The file ChangeLog in the gdb distribution approximates a blow-by-blow account. The most prolific contributors to this important, but low profile task are Andrew Cagney (responsible for over half the entries), Daniel Jacobowitz, Mark Kettenis, Jim Blandy and Eli Zaretskii.
Eli Zaretskii and Daniel Jacobowitz wrote the sections documenting watchpoints.
Jeremy Bennett updated the sections on initializing a new architecture and register representation, and added the section on Frame Interpretation.
gdb consists of three major subsystems: user interface, symbol handling (the symbol side), and target system handling (the target side).
The user interface consists of several actual interfaces, plus supporting code.
The symbol side consists of object file readers, debugging info interpreters, symbol table management, source language expression parsing, type and value printing.
The target side consists of execution control, stack frame analysis, and physical target manipulation.
The target side/symbol side division is not formal, and there are a number of exceptions. For instance, core file support involves symbolic elements (the basic core file reader is in BFD) and target elements (it supplies the contents of memory and the values of registers). Instead, this division is useful for understanding how the minor subsystems should fit together.
The symbolic side of gdb can be thought of as “everything you can do in gdb without having a live program running”. For instance, you can look at the types of variables, and evaluate many kinds of expressions.
The target side of gdb is the “bits and bytes manipulator”. Although it may make reference to symbolic info here and there, most of the target side will run with only a stripped executable available—or even no executable at all, in remote debugging cases.
Operations such as disassembly, stack frame crawls, and register display, are able to work with no symbolic info at all. In some cases, such as disassembly, gdb will use symbolic info to present addresses relative to symbols rather than as raw numbers, but it will work either way.
Host refers to attributes of the system where gdb runs. Target refers to the system where the program being debugged executes. In most cases they are the same machine, in which case a third type of Native attributes come into play.
Defines and include files needed to build on the host are host
support. Examples are tty support, system defined types, host byte
order, host float format. These are all calculated by autoconf
when the debugger is built.
Defines and information needed to handle the target format are target dependent. Examples are the stack frame format, instruction set, breakpoint instruction, registers, and how to set up and tear down the stack to call a function.
Information that is only needed when the host and target are the same,
is native dependent. One example is Unix child process support; if the
host and target are not the same, calling fork to start the target
process is a bad idea. The various macros needed for finding the
registers in the upage, running ptrace, and such are all
in the native-dependent files.
Another example of native-dependent code is support for features that
are really part of the target environment, but which require
#include files that are only available on the host system. Core
file handling and setjmp handling are two common cases.
When you want to make gdb work as the traditional native debugger on a system, you will need to supply both target and native information.
The gdb source directory has a mostly flat structure—there are only a few subdirectories. A file's name usually gives a hint as to what it does; for example, stabsread.c reads stabs, dwarf2read.c reads DWARF 2, etc.
Files that are related to some common task have names that share common substrings. For example, *-thread.c files deal with debugging threads on various platforms; *read.c files deal with reading various kinds of symbol and object files; inf*.c files deal with direct control of the inferior program (gdb parlance for the program being debugged).
There are several dozens of files in the *-tdep.c family. `tdep' stands for target-dependent code—each of these files implements debug support for a specific target architecture (sparc, mips, etc). Usually, only one of these will be used in a specific gdb configuration (sometimes two, closely related).
Similarly, there are many *-nat.c files, each one for native debugging on a specific system (e.g., sparc-linux-nat.c is for native debugging of Sparc machines running the Linux kernel).
The few subdirectories of the source tree are:
gdb uses a number of debugging-specific algorithms. They are often not very complicated, but get lost in the thicket of special cases and real-world issues. This chapter describes the basic algorithms and mentions some of the specific target definitions that they use.
To produce a backtrace and allow the user to manipulate older frames' variables and arguments, gdb needs to find the base addresses of older frames, and discover where those frames' registers have been saved. Since a frame's “callee-saves” registers get saved by younger frames if and when they're reused, a frame's registers may be scattered unpredictably across younger frames. This means that changing the value of a register-allocated variable in an older frame may actually entail writing to a save slot in some younger frame.
Modern versions of GCC emit Dwarf call frame information (“CFI”), which describes how to find frame base addresses and saved registers. But CFI is not always available, so as a fallback gdb uses a technique called prologue analysis to find frame sizes and saved registers. A prologue analyzer disassembles the function's machine code starting from its entry point, and looks for instructions that allocate frame space, save the stack pointer in a frame pointer register, save registers, and so on. Obviously, this can't be done accurately in general, but it's tractable to do well enough to be very helpful. Prologue analysis predates the GNU toolchain's support for CFI; at one time, prologue analysis was the only mechanism gdb used for stack unwinding at all, when the function calling conventions didn't specify a fixed frame layout.
In the olden days, function prologues were generated by hand-written, target-specific code in GCC, and treated as opaque and untouchable by optimizers. Looking at this code, it was usually straightforward to write a prologue analyzer for gdb that would accurately understand all the prologues GCC would generate. However, over time GCC became more aggressive about instruction scheduling, and began to understand more about the semantics of the prologue instructions themselves; in response, gdb's analyzers became more complex and fragile. Keeping the prologue analyzers working as GCC (and the instruction sets themselves) evolved became a substantial task.
To try to address this problem, the code in prologue-value.h and prologue-value.c provides a general framework for writing prologue analyzers that are simpler and more robust than ad-hoc analyzers. When we analyze a prologue using the prologue-value framework, we're really doing “abstract interpretation” or “pseudo-evaluation”: running the function's code in simulation, but using conservative approximations of the values registers and memory would hold when the code actually runs. For example, if our function starts with the instruction:
addi r1, 42 # add 42 to r1
we don't know exactly what value will be in r1 after executing
this instruction, but we do know it'll be 42 greater than its original
value.
If we then see an instruction like:
addi r1, 22 # add 22 to r1
we still don't know what r1's value is, but again, we can say
it is now 64 greater than its original value.
If the next instruction were:
mov r2, r1 # set r2 to r1's value
then we can say that r2's value is now the original value of
r1 plus 64.
It's common for prologues to save registers on the stack, so we'll need to track the values of stack frame slots, as well as the registers. So after an instruction like this:
mov (fp+4), r2
then we'd know that the stack slot four bytes above the frame pointer
holds the original value of r1 plus 64.
And so on.
Of course, this can only go so far before it gets unreasonable. If we
wanted to be able to say anything about the value of r1 after
the instruction:
xor r1, r3 # exclusive-or r1 and r3, place result in r1
then things would get pretty complex. But remember, we're just doing
a conservative approximation; if exclusive-or instructions aren't
relevant to prologues, we can just say r1's value is now
“unknown”. We can ignore things that are too complex, if that loss of
information is acceptable for our application.
So when we say “conservative approximation” here, what we mean is an approximation that is either accurate, or marked “unknown”, but never inaccurate.
Using this framework, a prologue analyzer is simply an interpreter for machine code, but one that uses conservative approximations for the contents of registers and memory instead of actual values. Starting from the function's entry point, you simulate instructions up to the current PC, or an instruction that you don't know how to simulate. Now you can examine the state of the registers and stack slots you've kept track of.
This does take some work. But prologue analyzers aren't quick-and-simple pattern patching to recognize a few fixed prologue forms any more; they're big, hairy functions. Along with inferior function calls, prologue analysis accounts for a substantial portion of the time needed to stabilize a gdb port. So it's worthwhile to look for an approach that will be easier to understand and maintain. In the approach described above:
The file prologue-value.h contains detailed comments explaining the framework and how to use it.
In general, a breakpoint is a user-designated location in the program where the user wants to regain control if program execution ever reaches that location.
There are two main ways to implement breakpoints; either as “hardware” breakpoints or as “software” breakpoints.
Hardware breakpoints are sometimes available as a builtin debugging features with some chips. Typically these work by having dedicated register into which the breakpoint address may be stored. If the PC (shorthand for program counter) ever matches a value in a breakpoint registers, the CPU raises an exception and reports it to gdb.
Another possibility is when an emulator is in use; many emulators include circuitry that watches the address lines coming out from the processor, and force it to stop if the address matches a breakpoint's address.
A third possibility is that the target already has the ability to do breakpoints somehow; for instance, a ROM monitor may do its own software breakpoints. So although these are not literally “hardware breakpoints”, from gdb's point of view they work the same; gdb need not do anything more than set the breakpoint and wait for something to happen.
Since they depend on hardware resources, hardware breakpoints may be limited in number; when the user asks for more, gdb will start trying to set software breakpoints. (On some architectures, notably the 32-bit x86 platforms, gdb cannot always know whether there's enough hardware resources to insert all the hardware breakpoints and watchpoints. On those platforms, gdb prints an error message only when the program being debugged is continued.)
Software breakpoints require gdb to do somewhat more work. The basic theory is that gdb will replace a program instruction with a trap, illegal divide, or some other instruction that will cause an exception, and then when it's encountered, gdb will take the exception and stop the program. When the user says to continue, gdb will restore the original instruction, single-step, re-insert the trap, and continue on.
Since it literally overwrites the program being tested, the program area must be writable, so this technique won't work on programs in ROM. It can also distort the behavior of programs that examine themselves, although such a situation would be highly unusual.
Also, the software breakpoint instruction should be the smallest size of instruction, so it doesn't overwrite an instruction that might be a jump target, and cause disaster when the program jumps into the middle of the breakpoint instruction. (Strictly speaking, the breakpoint must be no larger than the smallest interval between instructions that may be jump targets; perhaps there is an architecture where only even-numbered instructions may jumped to.) Note that it's possible for an instruction set not to have any instructions usable for a software breakpoint, although in practice only the ARC has failed to define such an instruction.
Basic breakpoint object handling is in breakpoint.c. However, much of the interesting breakpoint action is in infrun.c.
target_remove_breakpoint (bp_tgt)target_insert_breakpoint (bp_tgt)->placed_address. Returns zero for success,
non-zero for failure. On input, bp_tgt contains the address of the
breakpoint, and is otherwise initialized to zero. The fields of the
struct bp_target_info pointed to by bp_tgt are updated
to contain other information about the breakpoint on output. The field
placed_address may be updated if the breakpoint was placed at a
related address; the field shadow_contents contains the real
contents of the bytes where the breakpoint has been inserted,
if reading memory would return the breakpoint instead of the
underlying memory; the field shadow_len is the length of
memory cached in shadow_contents, if any; and the field
placed_size is optionally set and used by the target, if
it could differ from shadow_len.
For example, the remote target `Z0' packet does not require
shadowing memory, so shadow_len is left at zero. However,
the length reported by gdbarch_breakpoint_from_pc is cached in
placed_size, so that a matching `z0' packet can be
used to remove the breakpoint.
target_remove_hw_breakpoint (bp_tgt)target_insert_hw_breakpoint (bp_tgt)->placed_address. Returns zero for success,
non-zero for failure. See target_insert_breakpoint for
a description of the struct bp_target_info pointed to by
bp_tgt; the shadow_contents and
shadow_len members are not used for hardware breakpoints,
but placed_size may be.
gdb has support for figuring out that the target is doing a
longjmp and for stopping at the target of the jump, if we are
stepping. This is done with a few specialized internal breakpoints,
which are visible in the output of the `maint info breakpoint'
command.
To make this work, you need to define a function called
gdbarch_get_longjmp_target, which will examine the
jmp_buf structure and extract the longjmp target address.
Since jmp_buf is target specific and typically defined in a
target header not available to gdb, you will need to
determine the offset of the PC manually and return that; many targets
define a jb_pc_offset field in the tdep structure to save the
value once calculated.
Watchpoints are a special kind of breakpoints (see breakpoints) which break when data is accessed rather than when some instruction is executed. When you have data which changes without your knowing what code does that, watchpoints are the silver bullet to hunt down and kill such bugs.
Watchpoints can be either hardware-assisted or not; the latter type is known as “software watchpoints.” gdb always uses hardware-assisted watchpoints if they are available, and falls back on software watchpoints otherwise. Typical situations where gdb will use software watchpoints are:
Software watchpoints are very slow, since gdb needs to single-step the program being debugged and test the value of the watched expression(s) after each instruction. The rest of this section is mostly irrelevant for software watchpoints.
When the inferior stops, gdb tries to establish, among other
possible reasons, whether it stopped due to a watchpoint being hit.
It first uses STOPPED_BY_WATCHPOINT to see if any watchpoint
was hit. If not, all watchpoint checking is skipped.
Then gdb calls target_stopped_data_address exactly
once. This method returns the address of the watchpoint which
triggered, if the target can determine it. If the triggered address
is available, gdb compares the address returned by this
method with each watched memory address in each active watchpoint.
For data-read and data-access watchpoints, gdb announces
every watchpoint that watches the triggered address as being hit.
For this reason, data-read and data-access watchpoints
require that the triggered address be available; if not, read
and access watchpoints will never be considered hit. For data-write
watchpoints, if the triggered address is available, gdb
considers only those watchpoints which match that address;
otherwise, gdb considers all data-write watchpoints. For
each data-write watchpoint that gdb considers, it evaluates
the expression whose value is being watched, and tests whether the
watched value has changed. Watchpoints whose watched values have
changed are announced as hit.
gdb uses several macros and primitives to support hardware watchpoints:
TARGET_CAN_USE_HARDWARE_WATCHPOINT (type, count, other)TARGET_REGION_OK_FOR_HW_WATCHPOINT (addr, len)target_insert_watchpoint (addr, len, type)target_remove_watchpoint (addr, len, type)target_hw_bp_type,
defined by breakpoint.h as follows:
enum target_hw_bp_type
{
hw_write = 0, /* Common (write) HW watchpoint */
hw_read = 1, /* Read HW watchpoint */
hw_access = 2, /* Access (read or write) HW watchpoint */
hw_execute = 3 /* Execute HW breakpoint */
};
These two macros should return 0 for success, non-zero for failure.
target_stopped_data_address (addr_p)gdb will only call this method once per watchpoint stop,
immediately after calling STOPPED_BY_WATCHPOINT. If the
target's watchpoint indication is sticky, i.e., stays set after
resuming, this method should clear it. For instance, the x86 debug
control register has sticky triggered flags.
target_watchpoint_addr_within_range (target, addr, start, length)target_stopped_data_address)
lies within the hardware-defined watchpoint region described by
start and length. This only needs to be provided if the
granularity of a watchpoint is greater than one byte, i.e., if the
watchpoint can also trigger on nearby addresses outside of the watched
region.
HAVE_STEPPABLE_WATCHPOINTgdbarch_have_nonsteppable_watchpoint,
this is usually set when watchpoints trigger at the instruction
which will perform an interesting read or write. It should be
set if there is a temporary disable bit which allows the processor
to step over the interesting instruction without raising the
watchpoint exception again.
int gdbarch_have_nonsteppable_watchpoint (gdbarch)HAVE_CONTINUABLE_WATCHPOINTSTOPPED_BY_WATCHPOINT (wait_status)struct target_waitstatus, defined by target.h.
Normally, this macro is defined to invoke the function pointed to by
the to_stopped_by_watchpoint member of the structure (of the
type target_ops, defined on target.h) that describes the
target-specific operations; to_stopped_by_watchpoint ignores
the wait_status argument.
gdb does not require the non-zero value returned by
STOPPED_BY_WATCHPOINT to be 100% correct, so if a target cannot
determine for sure whether the inferior stopped due to a watchpoint,
it could return non-zero “just in case”.
gdb only supports process-wide watchpoints, which trigger
in all threads. gdb uses the thread ID to make watchpoints
act as if they were thread-specific, but it cannot set hardware
watchpoints that only trigger in a specific thread. Therefore, even
if the target supports threads, per-thread debug registers, and
watchpoints which only affect a single thread, it should set the
per-thread debug registers for all threads to the same value. On
gnu/Linux native targets, this is accomplished by using
ALL_LWPS in target_insert_watchpoint and
target_remove_watchpoint and by using
linux_set_new_thread to register a handler for newly created
threads.
gdb's gnu/Linux support only reports a single event
at a time, although multiple events can trigger simultaneously for
multi-threaded programs. When multiple events occur, linux-nat.c
queues subsequent events and returns them the next time the program
is resumed. This means that STOPPED_BY_WATCHPOINT and
target_stopped_data_address only need to consult the current
thread's state—the thread indicated by inferior_ptid. If
two threads have hit watchpoints simultaneously, those routines
will be called a second time for the second thread.
The 32-bit Intel x86 (a.k.a. ia32) processors feature special debug registers designed to facilitate debugging. gdb provides a generic library of functions that x86-based ports can use to implement support for watchpoints and hardware-assisted breakpoints. This subsection documents the x86 watchpoint facilities in gdb.
(At present, the library functions read and write debug registers directly, and are thus only available for native configurations.)
To use the generic x86 watchpoint support, a port should do the following:
I386_USE_GENERIC_WATCHPOINTS somewhere in the
target-dependent headers.
I386_USE_GENERIC_WATCHPOINTS.
NATDEPFILES (see NATDEPFILES).
I386_DR_LOW_* macros described
below. Typically, each macro should call a target-specific function
which does the real work.
The x86 watchpoint support works by maintaining mirror images of the debug registers. Values are copied between the mirror images and the real debug registers via a set of macros which each target needs to provide:
I386_DR_LOW_SET_CONTROL (val)I386_DR_LOW_SET_ADDR (idx, addr)I386_DR_LOW_RESET_ADDR (idx)I386_DR_LOW_GET_STATUSI386_DR_LOW_GET_STATUS, so as to support per-thread status
register values.
For each one of the 4 debug registers (whose indices are from 0 to 3) that store addresses, a reference count is maintained by gdb, to allow sharing of debug registers by several watchpoints. This allows users to define several watchpoints that watch the same expression, but with different conditions and/or commands, without wasting debug registers which are in short supply. gdb maintains the reference counts internally, targets don't have to do anything to use this feature.
The x86 debug registers can each watch a region that is 1, 2, or 4 bytes long. The ia32 architecture requires that each watched region be appropriately aligned: 2-byte region on 2-byte boundary, 4-byte region on 4-byte boundary. However, the x86 watchpoint support in gdb can watch unaligned regions and regions larger than 4 bytes (up to 16 bytes) by allocating several debug registers to watch a single region. This allocation of several registers per a watched region is also done automatically without target code intervention.
The generic x86 watchpoint support provides the following API for the gdb's application code:
i386_region_ok_for_watchpoint (addr, len)TARGET_REGION_OK_FOR_HW_WATCHPOINT is set to call
this function. It counts the number of debug registers required to
watch a given region, and returns a non-zero value if that number is
less than 4, the number of debug registers available to x86
processors.
i386_stopped_data_address (addr_p)target_stopped_data_address is set to call this function.
This
function examines the breakpoint condition bits in the DR6 Debug
Status register, as returned by the I386_DR_LOW_GET_STATUS
macro, and returns the address associated with the first bit that is
set in DR6.
i386_stopped_by_watchpoint (void)STOPPED_BY_WATCHPOINT
is set to call this function. The
argument passed to STOPPED_BY_WATCHPOINT is ignored. This
function examines the breakpoint condition bits in the DR6 Debug
Status register, as returned by the I386_DR_LOW_GET_STATUS
macro, and returns true if any bit is set. Otherwise, false is
returned.
i386_insert_watchpoint (addr, len, type)i386_remove_watchpoint (addr, len, type)target_insert_watchpoint and target_remove_watchpoint
are set to call these functions. i386_insert_watchpoint first
looks for a debug register which is already set to watch the same
region for the same access types; if found, it just increments the
reference count of that debug register, thus implementing debug
register sharing between watchpoints. If no such register is found,
the function looks for a vacant debug register, sets its mirrored
value to addr, sets the mirrored value of DR7 Debug Control
register as appropriate for the len and type parameters,
and then passes the new values of the debug register and DR7 to the
inferior by calling I386_DR_LOW_SET_ADDR and
I386_DR_LOW_SET_CONTROL. If more than one debug register is
required to cover the given region, the above process is repeated for
each debug register.
i386_remove_watchpoint does the opposite: it resets the address
in the mirrored value of the debug register and its read/write and
length bits in the mirrored value of DR7, then passes these new
values to the inferior via I386_DR_LOW_RESET_ADDR and
I386_DR_LOW_SET_CONTROL. If a register is shared by several
watchpoints, each time a i386_remove_watchpoint is called, it
decrements the reference count, and only calls
I386_DR_LOW_RESET_ADDR and I386_DR_LOW_SET_CONTROL when
the count goes to zero.
i386_insert_hw_breakpoint (bp_tgt)i386_remove_hw_breakpoint (bp_tgt)target_insert_hw_breakpoint and
target_remove_hw_breakpoint are set to call these functions.
The argument is a struct bp_target_info *, as described in
the documentation for target_insert_breakpoint.
These functions work like i386_insert_watchpoint and
i386_remove_watchpoint, respectively, except that they set up
the debug registers to watch instruction execution, and each
hardware-assisted breakpoint always requires exactly one debug
register.
i386_cleanup_dregs (void)Notes:
enum target_hw_bp_type doesn't even have an enumeration for I/O
watchpoints, this feature is not yet available to gdb running
on x86.
In the abstract, a checkpoint is a point in the execution history of the program, which the user may wish to return to at some later time.
Internally, a checkpoint is a saved copy of the program state, including whatever information is required in order to restore the program to that state at a later time. This can be expected to include the state of registers and memory, and may include external state such as the state of open files and devices.
There are a number of ways in which checkpoints may be implemented in gdb, e.g. as corefiles, as forked processes, and as some opaque method implemented on the target side.
A corefile can be used to save an image of target memory and register state, which can in principle be restored later — but corefiles do not typically include information about external entities such as open files. Currently this method is not implemented in gdb.
A forked process can save the state of user memory and registers, as well as some subset of external (kernel) state. This method is used to implement checkpoints on Linux, and in principle might be used on other systems.
Some targets, e.g. simulators, might have their own built-in method for saving checkpoints, and gdb might be able to take advantage of that capability without necessarily knowing any details of how it is done.
In order to function properly, several modules need to be notified when some changes occur in the gdb internals. Traditionally, these modules have relied on several paradigms, the most common ones being hooks and gdb-events. Unfortunately, none of these paradigms was versatile enough to become the standard notification mechanism in gdb. The fact that they only supported one “client” was also a strong limitation.
A new paradigm, based on the Observer pattern of the Design Patterns book, has therefore been implemented. The goal was to provide a new interface overcoming the issues with the notification mechanisms previously available. This new interface needed to be strongly typed, easy to extend, and versatile enough to be used as the standard interface when adding new notifications.
See GDB Observers for a brief description of the observers currently implemented in GDB. The rationale for the current implementation is also briefly discussed.
gdb has several user interfaces, of which the traditional command-line interface is perhaps the most familiar.
The command interpreter in gdb is fairly simple. It is designed to allow for the set of commands to be augmented dynamically, and also has a recursive subcommand capability, where the first argument to a command may itself direct a lookup on a different command list.
For instance, the `set' command just starts a lookup on the
setlist command list, while `set thread' recurses
to the set_thread_cmd_list.
To add commands in general, use add_cmd. add_com adds to
the main command list, and should be used for those commands. The usual
place to add commands is in the _initialize_xyz routines at
the ends of most source files.
To add paired `set' and `show' commands, use
add_setshow_cmd or add_setshow_cmd_full. The former is
a slightly simpler interface which is useful when you don't need to
further modify the new command structures, while the latter returns
the new command structures for manipulation.
Before removing commands from the command set it is a good idea to
deprecate them for some time. Use deprecate_cmd on commands or
aliases to set the deprecated flag. deprecate_cmd takes a
struct cmd_list_element as it's first argument. You can use the
return value from add_com or add_cmd to deprecate the
command immediately after it is created.
The first time a command is used the user will be warned and offered a
replacement (if one exists). Note that the replacement string passed to
deprecate_cmd should be the full name of the command, i.e., the
entire string the user should type at the command line.
ui_out FunctionsThe ui_out functions present an abstraction level for the
gdb output code. They hide the specifics of different user
interfaces supported by gdb, and thus free the programmer
from the need to write several versions of the same code, one each for
every UI, to produce output.
In general, execution of each gdb command produces some sort of output, and can even generate an input request.
Output can be generated for the following purposes:
This section mainly concentrates on how to build result output, although some of it also applies to other kinds of output.
Generation of output that displays the results of an operation involves one or more of the following:
The ui_out routines take care of the first three aspects.
Annotations are provided by separate annotation routines. Note that use
of annotations for an interface between a GUI and gdb is
deprecated.
Output can be in the form of a single item, which we call a field; a list consisting of identical fields; a tuple consisting of non-identical fields; or a table, which is a tuple consisting of a header and a body. In a BNF-like form:
<table> ==><header> <body>
<header> ==>{ <column> }
<column> ==><width> <alignment> <title>
<body> ==>{<row>}
Most ui_out routines are of type void, the exceptions are
ui_out_stream_new (which returns a pointer to the newly created
object) and the make_cleanup routines.
The first parameter is always the ui_out vector object, a pointer
to a struct ui_out.
The format parameter is like in printf family of functions.
When it is present, there must also be a variable list of arguments
sufficient used to satisfy the % specifiers in the supplied
format.
When a character string argument is not used in a ui_out function
call, a NULL pointer has to be supplied instead.
This section introduces ui_out routines for building lists,
tuples and tables. The routines to output the actual data items
(fields) are presented in the next section.
To recap: A tuple is a sequence of fields, each field containing information about an object; a list is a sequence of fields where each field describes an identical object.
Use the table functions when your output consists of a list of rows (tuples) and the console output should include a heading. Use this even when you are listing just one object but you still want the header.
Tables can not be nested. Tuples and lists can be nested up to a maximum of five levels.
The overall structure of the table output code is something like this:
ui_out_table_begin
ui_out_table_header
...
ui_out_table_body
ui_out_tuple_begin
ui_out_field_*
...
ui_out_tuple_end
...
ui_out_table_end
Here is the description of table-, tuple- and list-related ui_out
functions:
The function
ui_out_table_beginmarks the beginning of the output of a table. It should always be called before any otherui_outfunction for a given table. nbrofcols is the number of columns in the table. nr_rows is the number of rows in the table. tblid is an optional string identifying the table. The string pointed to by tblid is copied by the implementation ofui_out_table_begin, so the application can free the string if it wasmalloced.The companion function
ui_out_table_end, described below, marks the end of the table's output.
ui_out_table_headerprovides the header information for a single table column. You call this function several times, one each for every column of the table, afterui_out_table_begin, but beforeui_out_table_body.The value of width gives the column width in characters. The value of alignment is one of
left,center, andright, and it specifies how to align the header: left-justify, center, or right-justify it. colhdr points to a string that specifies the column header; the implementation copies that string, so column header strings inmalloced storage can be freed after the call.
This function delimits the table header from the table body.
This function signals the end of a table's output. It should be called after the table body has been produced by the list and field output functions.
There should be exactly one call to
ui_out_table_endfor each call toui_out_table_begin, otherwise theui_outfunctions will signal an internal error.
The output of the tuples that represent the table rows must follow the
call to ui_out_table_body and precede the call to
ui_out_table_end. You build a tuple by calling
ui_out_tuple_begin and ui_out_tuple_end, with suitable
calls to functions which actually output fields between them.
This function marks the beginning of a tuple output. id points to an optional string that identifies the tuple; it is copied by the implementation, and so strings in
malloced storage can be freed after the call.
This function signals an end of a tuple output. There should be exactly one call to
ui_out_tuple_endfor each call toui_out_tuple_begin, otherwise an internal gdb error will be signaled.
This function first opens the tuple and then establishes a cleanup (see Cleanups) to close the tuple. It provides a convenient and correct implementation of the non-portable1 code sequence:
struct cleanup *old_cleanup; ui_out_tuple_begin (uiout, "..."); old_cleanup = make_cleanup ((void(*)(void *)) ui_out_tuple_end, uiout);
This function marks the beginning of a list output. id points to an optional string that identifies the list; it is copied by the implementation, and so strings in
malloced storage can be freed after the call.
This function signals an end of a list output. There should be exactly one call to
ui_out_list_endfor each call toui_out_list_begin, otherwise an internal gdb error will be signaled.
Similar to
make_cleanup_ui_out_tuple_begin_end, this function opens a list and then establishes cleanup (see Cleanups) that will close the list.
The functions described below produce output for the actual data items, or fields, which contain information about the object.
Choose the appropriate function accordingly to your particular needs.
This is the most general output function. It produces the representation of the data in the variable-length argument list according to formatting specifications in format, a
printf-like format string. The optional argument fldname supplies the name of the field. The data items themselves are supplied as additional arguments after format.This generic function should be used only when it is not possible to use one of the specialized versions (see below).
This function outputs a value of an
intvariable. It uses the"%d"output conversion specification. fldname specifies the name of the field.
This function outputs a value of an
intvariable. It differs fromui_out_field_intin that the caller specifies the desired width and alignment of the output. fldname specifies the name of the field.
This function outputs an address as appropriate for gdbarch.
This function outputs a string using the
"%s"conversion specification.
Sometimes, there's a need to compose your output piece by piece using
functions that operate on a stream, such as value_print or
fprintf_symbol_filtered. These functions accept an argument of
the type struct ui_file *, a pointer to a ui_file object
used to store the data stream used for the output. When you use one
of these functions, you need a way to pass their results stored in a
ui_file object to the ui_out functions. To this end,
you first create a ui_stream object by calling
ui_out_stream_new, pass the stream member of that
ui_stream object to value_print and similar functions,
and finally call ui_out_field_stream to output the field you
constructed. When the ui_stream object is no longer needed,
you should destroy it and free its memory by calling
ui_out_stream_delete.
This function creates a new
ui_streamobject which uses the same output methods as theui_outobject whose pointer is passed in uiout. It returns a pointer to the newly createdui_streamobject.
This functions destroys a
ui_streamobject specified by streambuf.
This function consumes all the data accumulated in
streambuf->streamand outputs it likeui_out_field_stringdoes. After a call toui_out_field_stream, the accumulated data no longer exists, but the stream is still valid and may be used for producing more fields.
Important: If there is any chance that your code could bail
out before completing output generation and reaching the point where
ui_out_stream_delete is called, it is necessary to set up a
cleanup, to avoid leaking memory and other resources. Here's a
skeleton code to do that:
struct ui_stream *mybuf = ui_out_stream_new (uiout);
struct cleanup *old = make_cleanup (ui_out_stream_delete, mybuf);
...
do_cleanups (old);
If the function already has the old cleanup chain set (for other kinds of cleanups), you just have to add your cleanup to it:
mybuf = ui_out_stream_new (uiout);
make_cleanup (ui_out_stream_delete, mybuf);
Note that with cleanups in place, you should not call
ui_out_stream_delete directly, or you would attempt to free the
same buffer twice.
This function skips a field in a table. Use it if you have to leave an empty field without disrupting the table alignment. The argument fldname specifies a name for the (missing) filed.
This function outputs the text in string in a way that makes it easy to be read by humans. For example, the console implementation of this method filters the text through a built-in pager, to prevent it from scrolling off the visible portion of the screen.
Use this function for printing relatively long chunks of text around the actual field data: the text it produces is not aligned according to the table's format. Use
ui_out_field_stringto output a string field, and useui_out_message, described below, to output short messages.
This function outputs nspaces spaces. It is handy to align the text produced by
ui_out_textwith the rest of the table or list.
This function produces a formatted message, provided that the current verbosity level is at least as large as given by verbosity. The current verbosity level is specified by the user with the `set verbositylevel' command.2
This function gives the console output filter (a paging filter) a hint of where to break lines which are too long. Ignored for all other output consumers. indent, if non-
NULL, is the string to be printed to indent the wrapped text on the next line; it must remain accessible until the next call toui_out_wrap_hint, or until an explicit newline is produced by one of the other functions. If indent isNULL, the wrapped text will not be indented.
This function flushes whatever output has been accumulated so far, if the UI buffers output.
ui_out functionsThis section gives some practical examples of using the ui_out
functions to generalize the old console-oriented code in
gdb. The examples all come from functions defined on the
breakpoints.c file.
This example, from the breakpoint_1 function, shows how to
produce a table.
The original code was:
if (!found_a_breakpoint++)
{
annotate_breakpoints_headers ();
annotate_field (0);
printf_filtered ("Num ");
annotate_field (1);
printf_filtered ("Type ");
annotate_field (2);
printf_filtered ("Disp ");
annotate_field (3);
printf_filtered ("Enb ");
if (addressprint)
{
annotate_field (4);
printf_filtered ("Address ");
}
annotate_field (5);
printf_filtered ("What\n");
annotate_breakpoints_table ();
}
Here's the new version:
nr_printable_breakpoints = ...;
if (addressprint)
ui_out_table_begin (ui, 6, nr_printable_breakpoints, "BreakpointTable");
else
ui_out_table_begin (ui, 5, nr_printable_breakpoints, "BreakpointTable");
if (nr_printable_breakpoints > 0)
annotate_breakpoints_headers ();
if (nr_printable_breakpoints > 0)
annotate_field (0);
ui_out_table_header (uiout, 3, ui_left, "number", "Num"); /* 1 */
if (nr_printable_breakpoints > 0)
annotate_field (1);
ui_out_table_header (uiout, 14, ui_left, "type", "Type"); /* 2 */
if (nr_printable_breakpoints > 0)
annotate_field (2);
ui_out_table_header (uiout, 4, ui_left, "disp", "Disp"); /* 3 */
if (nr_printable_breakpoints > 0)
annotate_field (3);
ui_out_table_header (uiout, 3, ui_left, "enabled", "Enb"); /* 4 */
if (addressprint)
{
if (nr_printable_breakpoints > 0)
annotate_field (4);
if (print_address_bits <= 32)
ui_out_table_header (uiout, 10, ui_left, "addr", "Address");/* 5 */
else
ui_out_table_header (uiout, 18, ui_left, "addr", "Address");/* 5 */
}
if (nr_printable_breakpoints > 0)
annotate_field (5);
ui_out_table_header (uiout, 40, ui_noalign, "what", "What"); /* 6 */
ui_out_table_body (uiout);
if (nr_printable_breakpoints > 0)
annotate_breakpoints_table ();
This example, from the print_one_breakpoint function, shows how
to produce the actual data for the table whose structure was defined
in the above example. The original code was:
annotate_record ();
annotate_field (0);
printf_filtered ("%-3d ", b->number);
annotate_field (1);
if ((int)b->type > (sizeof(bptypes)/sizeof(bptypes[0]))
|| ((int) b->type != bptypes[(int) b->type].type))
internal_error ("bptypes table does not describe type #%d.",
(int)b->type);
printf_filtered ("%-14s ", bptypes[(int)b->type].description);
annotate_field (2);
printf_filtered ("%-4s ", bpdisps[(int)b->disposition]);
annotate_field (3);
printf_filtered ("%-3c ", bpenables[(int)b->enable]);
...
This is the new version:
annotate_record ();
ui_out_tuple_begin (uiout, "bkpt");
annotate_field (0);
ui_out_field_int (uiout, "number", b->number);
annotate_field (1);
if (((int) b->type > (sizeof (bptypes) / sizeof (bptypes[0])))
|| ((int) b->type != bptypes[(int) b->type].type))
internal_error ("bptypes table does not describe type #%d.",
(int) b->type);
ui_out_field_string (uiout, "type", bptypes[(int)b->type].description);
annotate_field (2);
ui_out_field_string (uiout, "disp", bpdisps[(int)b->disposition]);
annotate_field (3);
ui_out_field_fmt (uiout, "enabled", "%c", bpenables[(int)b->enable]);
...
This example, also from print_one_breakpoint, shows how to
produce a complicated output field using the print_expression
functions which requires a stream to be passed. It also shows how to
automate stream destruction with cleanups. The original code was:
annotate_field (5);
print_expression (b->exp, gdb_stdout);
The new version is:
struct ui_stream *stb = ui_out_stream_new (uiout);
struct cleanup *old_chain = make_cleanup_ui_out_stream_delete (stb);
...
annotate_field (5);
print_expression (b->exp, stb->stream);
ui_out_field_stream (uiout, "what", local_stream);
This example, also from print_one_breakpoint, shows how to use
ui_out_text and ui_out_field_string. The original code
was:
annotate_field (5);
if (b->dll_pathname == NULL)
printf_filtered ("<any library> ");
else
printf_filtered ("library \"%s\" ", b->dll_pathname);
It became:
annotate_field (5);
if (b->dll_pathname == NULL)
{
ui_out_field_string (uiout, "what", "<any library>");
ui_out_spaces (uiout, 1);
}
else
{
ui_out_text (uiout, "library \"");
ui_out_field_string (uiout, "what", b->dll_pathname);
ui_out_text (uiout, "\" ");
}
The following example from print_one_breakpoint shows how to
use ui_out_field_int and ui_out_spaces. The original
code was:
annotate_field (5);
if (b->forked_inferior_pid != 0)
printf_filtered ("process %d ", b->forked_inferior_pid);
It became:
annotate_field (5);
if (b->forked_inferior_pid != 0)
{
ui_out_text (uiout, "process ");
ui_out_field_int (uiout, "what", b->forked_inferior_pid);
ui_out_spaces (uiout, 1);
}
Here's an example of using ui_out_field_string. The original
code was:
annotate_field (5);
if (b->exec_pathname != NULL)
printf_filtered ("program \"%s\" ", b->exec_pathname);
It became:
annotate_field (5);
if (b->exec_pathname != NULL)
{
ui_out_text (uiout, "program \"");
ui_out_field_string (uiout, "what", b->exec_pathname);
ui_out_text (uiout, "\" ");
}
Finally, here's an example of printing an address. The original code:
annotate_field (4);
printf_filtered ("%s ",
hex_string_custom ((unsigned long) b->address, 8));
It became:
annotate_field (4);
ui_out_field_core_addr (uiout, "Address", b->address);
libgdb 1.0 was an abortive project of years ago. The theory was
to provide an API to gdb's functionality.
libgdb 2.0 is an ongoing effort to update gdb so that is
better able to support graphical and other environments.
Since libgdb development is on-going, its architecture is still
evolving. The following components have so far been identified:
The model that ties these components together is described below.
libgdb ModelA client of libgdb interacts with the library in two ways.
libgdb of any internal state changes (break point changes, run
state, etc).
libgdb (using the ui-out builder) to
obtain various status values from gdb.
Since libgdb could have multiple clients (e.g., a GUI supporting
the existing gdb CLI), those clients must co-operate when
controlling libgdb. In particular, a client must ensure that
libgdb is idle (i.e. no other client is using libgdb)
before responding to a gdb-event by making a query.
At present gdb's CLI is very much entangled in with the core of
libgdb. Consequently, a client wishing to include the CLI in
their interface needs to carefully co-ordinate its own and the CLI's
requirements.
It is suggested that the client set libgdb up to be bi-modal
(alternate between CLI and client query modes). The notes below sketch
out the theory:
libgdb.
cli-out builder using its own
versions of the ui-file gdb_stderr, gdb_stdtarg and
gdb_stdout streams.
ui-out builder that is only
used while making direct queries to libgdb.
When the client receives input intended for the CLI, it simply passes it
along. Since the cli-out builder is installed by default, all
the CLI output in response to that command is routed (pronounced rooted)
through to the client controlled gdb_stdout et. al. streams.
At the same time, the client is kept abreast of internal changes by
virtue of being a libgdb observer.
The only restriction on the client is that it must wait until
libgdb becomes idle before initiating any queries (using the
client's custom builder).
libgdb componentsgdb-events provides the client with a very raw mechanism that can
be used to implement an observer. At present it only allows for one
observer and that observer must, internally, handle the need to delay
the processing of any event notifications until after libgdb has
finished the current command.
ui-out provides the infrastructure necessary for a client to
create a builder. That builder is then passed down to libgdb
when doing any queries.
event-loop, currently non-re-entrant, provides a simple event loop. A client would need to either plug its self into this loop or, implement a new event-loop that gdb would use.
The event-loop will eventually be made re-entrant. This is so that gdb can better handle the problem of some commands blocking instead of returning.
libgdb is the most obvious component of this system. It provides
the query interface. Each function is parameterized by a ui-out
builder. The result of the query is constructed using that builder
before the query function returns.
gdb uses struct value, or values, as an internal
abstraction for the representation of a variety of inferior objects
and gdb convenience objects.
Values have an associated struct type, that describes a virtual
view of the raw data or object stored in or accessed through the
value.
A value is in addition discriminated by its lvalue-ness, given its
enum lval_type enumeration type:
not_lvallval_memorylval_registerlval_internalvarlval_internalvar_componentlval_computedPointers to these functions are stored in a struct lval_funcs
instance (declared in value.h), and passed to the
allocate_computed_value function, as in the example below.
static void
nil_value_read (struct value *v)
{
/* This callback reads data from some backend, and stores it in V.
In this case, we always read null data. You'll want to fill in
something more interesting. */
memset (value_contents_all_raw (v),
value_offset (v),
TYPE_LENGTH (value_type (v)));
}
static void
nil_value_write (struct value *v, struct value *fromval)
{
/* Takes the data from FROMVAL and stores it in the backend of V. */
to_oblivion (value_contents_all_raw (fromval),
value_offset (v),
TYPE_LENGTH (value_type (fromval)));
}
static struct lval_funcs nil_value_funcs =
{
nil_value_read,
nil_value_write
};
struct value *
make_nil_value (void)
{
struct type *type;
struct value *v;
type = make_nils_type ();
v = allocate_computed_value (type, &nil_value_funcs, NULL);
return v;
}
See the implementation of the $_siginfo convenience variable in
infrun.c as a real example use of lval_computed.
A frame is a construct that gdb uses to keep track of calling and called functions.
gdb's frame model, a fresh design, was implemented with the need to support dwarf's Call Frame Information in mind. In fact, the term “unwind” is taken directly from that specification. Developers wishing to learn more about unwinders, are encouraged to read the dwarf specification, available from http://www.dwarfstd.org.
gdb's model is that you find a frame's registers by
“unwinding” them from the next younger frame. That is,
`get_frame_register' which returns the value of a register in
frame #1 (the next-to-youngest frame), is implemented by calling frame
#0's frame_register_unwind (the youngest frame). But then the
obvious question is: how do you access the registers of the youngest
frame itself?
To answer this question, gdb has the sentinel frame, the
“-1st” frame. Unwinding registers from the sentinel frame gives you
the current values of the youngest real frame's registers. If f
is a sentinel frame, then get_frame_type (f) ==
SENTINEL_FRAME.
The architecture registers a list of frame unwinders (struct
frame_unwind), using the functions
frame_unwind_prepend_unwinder and
frame_unwind_append_unwinder. Each unwinder includes a
sniffer. Whenever gdb needs to unwind a frame (to fetch the
previous frame's registers or the current frame's ID), it calls
registered sniffers in order to find one which recognizes the frame.
The first time a sniffer returns non-zero, the corresponding unwinder
is assigned to the frame.
Every frame has an associated ID, of type struct frame_id.
The ID includes the stack base and function start address for
the frame. The ID persists through the entire life of the frame,
including while other called frames are running; it is used to
locate an appropriate struct frame_info from the cache.
Every time the inferior stops, and at various other times, the frame
cache is flushed. Because of this, parts of gdb which need
to keep track of individual frames cannot use pointers to struct
frame_info. A frame ID provides a stable reference to a frame, even
when the unwinder must be run again to generate a new struct
frame_info for the same frame.
The frame's unwinder's this_id method is called to find the ID.
Note that this is different from register unwinding, where the next
frame's prev_register is called to unwind this frame's
registers.
Both stack base and function address are required to identify the frame, because a recursive function has the same function address for two consecutive frames and a leaf function may have the same stack address as its caller. On some platforms, a third address is part of the ID to further disambiguate frames—for instance, on IA-64 the separate register stack address is included in the ID.
An invalid frame ID (outer_frame_id) returned from the
this_id method means to stop unwinding after this frame.
null_frame_id is another invalid frame ID which should be used
when there is no frame. For instance, certain breakpoints are attached
to a specific frame, and that frame is identified through its frame ID
(we use this to implement the "finish" command). Using
null_frame_id as the frame ID for a given breakpoint means
that the breakpoint is not specific to any frame. The this_id
method should never return null_frame_id.
Each unwinder includes a prev_register method. This method
takes a frame, an associated cache pointer, and a register number.
It returns a struct value * describing the requested register,
as saved by this frame. This is the value of the register that is
current in this frame's caller.
The returned value must have the same type as the register. It may have any lvalue type. In most circumstances one of these routines will generate the appropriate value:
frame_unwind_got_optimizedframe_unwind_got_registerframe_unwind_got_memoryframe_unwind_got_constantframe_unwind_got_addressframe_unwind_got_constant, except that the value is a target
address. This is frequently used for the stack pointer, which is not
explicitly saved but has a known offset from this frame's stack
pointer. For architectures with a flat unified address space, this is
generally the same as frame_unwind_got_constant.
Symbols are a key part of gdb's operation. Symbols include variables, functions, and types.
Symbol information for a large program can be truly massive, and reading of symbol information is one of the major performance bottlenecks in gdb; it can take many minutes to process it all. Studies have shown that nearly all the time spent is computational, rather than file reading.
One of the ways for gdb to provide a good user experience is to start up quickly, taking no more than a few seconds. It is simply not possible to process all of a program's debugging info in that time, and so we attempt to handle symbols incrementally. For instance, we create partial symbol tables consisting of only selected symbols, and only expand them to full symbol tables when necessary.
gdb reads symbols from symbol files. The usual symbol file is the file containing the program which gdb is debugging. gdb can be directed to use a different file for symbols (with the `symbol-file' command), and it can also read more symbols via the `add-file' and `load' commands. In addition, it may bring in more symbols while loading shared libraries.
Symbol files are initially opened by code in symfile.c using
the BFD library (see Support Libraries). BFD identifies the type
of the file by examining its header. find_sym_fns then uses
this identification to locate a set of symbol-reading functions.
Symbol-reading modules identify themselves to gdb by calling
add_symtab_fns during their module initialization. The argument
to add_symtab_fns is a struct sym_fns which contains the
name (or name prefix) of the symbol format, the length of the prefix,
and pointers to four functions. These functions are called at various
times to process symbol files whose identification matches the specified
prefix.
The functions supplied by each module are:
_symfile_init(struct sym_fns *sf)symbol_file_add when we are about to read a new
symbol file. This function should clean up any internal state (possibly
resulting from half-read previous files, for example) and prepare to
read a new symbol file. Note that the symbol file which we are reading
might be a new “main” symbol file, or might be a secondary symbol file
whose symbols are being added to the existing symbol table.
The argument to xyz_symfile_init is a newly allocated
struct sym_fns whose bfd field contains the BFD for the
new symbol file being read. Its private field has been zeroed,
and can be modified as desired. Typically, a struct of private
information will be malloc'd, and a pointer to it will be placed
in the private field.
There is no result from xyz_symfile_init, but it can call
error if it detects an unavoidable problem.
_new_init()symbol_file_add when discarding existing symbols.
This function needs only handle the symbol-reading module's internal
state; the symbol table data structures visible to the rest of
gdb will be discarded by symbol_file_add. It has no
arguments and no result. It may be called after
xyz_symfile_init, if a new symbol table is being read, or
may be called alone if all symbols are simply being discarded.
_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)symbol_file_add to actually read the symbols from a
symbol-file into a set of psymtabs or symtabs.
sf points to the struct sym_fns originally passed to
xyz_sym_init for possible initialization. addr is
the offset between the file's specified start address and its true
address in memory. mainline is 1 if this is the main symbol
table being read, and 0 if a secondary symbol file (e.g., shared library
or dynamically loaded file) is being read.
In addition, if a symbol-reading module creates psymtabs when
xyz_symfile_read is called, these psymtabs will contain a pointer
to a function xyz_psymtab_to_symtab, which can be called
from any point in the gdb symbol-handling code.
_psymtab_to_symtab (struct partial_symtab *pst)psymtab_to_symtab (or the PSYMTAB_TO_SYMTAB macro) if
the psymtab has not already been read in and had its pst->symtab
pointer set. The argument is the psymtab to be fleshed-out into a
symtab. Upon return, pst->readin should have been set to 1, and
pst->symtab should contain a pointer to the new corresponding symtab, or
zero if there were no symbols in that part of the symbol file.
gdb has three types of symbol tables:
This section describes partial symbol tables.
A psymtab is constructed by doing a very quick pass over an executable file's debugging information. Small amounts of information are extracted—enough to identify which parts of the symbol table will need to be re-read and fully digested later, when the user needs the information. The speed of this pass causes gdb to start up very quickly. Later, as the detailed rereading occurs, it occurs in small pieces, at various times, and the delay therefrom is mostly invisible to the user.
The symbols that show up in a file's psymtab should be, roughly, those
visible to the debugger's user when the program is not running code from
that file. These include external symbols and types, static symbols and
types, and enum values declared at file scope.
The psymtab also contains the range of instruction addresses that the full symbol table would represent.
The idea is that there are only two ways for the user (or much of the code in the debugger) to reference a symbol:
find_pc_function, find_pc_line, and other
find_pc_... functions handle this.
lookup_symbol
does most of the work here.
The only reason that psymtabs exist is to cause a symtab to be read in at the right moment. Any symbol that can be elided from a psymtab, while still causing that to happen, should not appear in it. Since psymtabs don't have the idea of scope, you can't put local symbols in them anyway. Psymtabs don't have the idea of the type of a symbol, either, so types need not appear, unless they will be referenced by name.
It is a bug for gdb to behave one way when only a psymtab has been read, and another way if the corresponding symtab has been read in. Such bugs are typically caused by a psymtab that does not contain all the visible symbols, or which has the wrong instruction address ranges.
The psymtab for a particular section of a symbol file (objfile) could be thrown away after the symtab has been read in. The symtab should always be searched before the psymtab, so the psymtab will never be used (in a bug-free environment). Currently, psymtabs are allocated on an obstack, and all the psymbols themselves are allocated in a pair of large arrays on an obstack, so there is little to be gained by trying to free them unless you want to do a lot more work.
Whether or not psymtabs are created depends on the objfile's symbol reader. The core of gdb hides the details of partial symbols and partial symbol tables behind a set of function pointers known as the quick symbol functions. These are documented in symfile.h.
FT_VOID, FT_BOOLEAN).These are the fundamental types that gdb uses internally. Fundamental types from the various debugging formats (stabs, ELF, etc) are mapped into one of these. They are basically a union of all fundamental types that gdb knows about for all the languages that gdb knows about.
TYPE_CODE_PTR, TYPE_CODE_ARRAY).Each time gdb builds an internal type, it marks it with one
of these types. The type may be a fundamental type, such as
TYPE_CODE_INT, or a derived type, such as TYPE_CODE_PTR
which is a pointer to another type. Typically, several FT_*
types map to one TYPE_CODE_* type, and are distinguished by
other members of the type struct, such as whether the type is signed
or unsigned, and how many bits it uses.
builtin_type_void, builtin_type_char).These are instances of type structs that roughly correspond to
fundamental types and are created as global types for gdb to
use for various ugly historical reasons. We eventually want to
eliminate these. Note for example that builtin_type_int
initialized in gdbtypes.c is basically the same as a
TYPE_CODE_INT type that is initialized in c-lang.c for
an FT_INTEGER fundamental type. The difference is that the
builtin_type is not associated with any particular objfile, and
only one instance exists, while c-lang.c builds as many
TYPE_CODE_INT types as needed, with each one associated with
some particular objfile.
The a.out format is the original file format for Unix. It
consists of three sections: text, data, and bss,
which are for program code, initialized data, and uninitialized data,
respectively.
The a.out format is so simple that it doesn't have any reserved
place for debugging information. (Hey, the original Unix hackers used
`adb', which is a machine-language debugger!) The only debugging
format for a.out is stabs, which is encoded as a set of normal
symbols with distinctive attributes.
The basic a.out reader is in dbxread.c.
The COFF format was introduced with System V Release 3 (SVR3) Unix. COFF files may have multiple sections, each prefixed by a header. The number of sections is limited.
The COFF specification includes support for debugging. Although this was a step forward, the debugging information was woefully limited. For instance, it was not possible to represent code that came from an included file. GNU's COFF-using configs often use stabs-type info, encapsulated in special sections.
The COFF reader is in coffread.c.
ECOFF is an extended COFF originally introduced for Mips and Alpha workstations.
The basic ECOFF reader is in mipsread.c.
The IBM RS/6000 running AIX uses an object file format called XCOFF.
The COFF sections, symbols, and line numbers are used, but debugging
symbols are dbx-style stabs whose strings are located in the
.debug section (rather than the string table). For more
information, see Top.
The shared library scheme has a clean interface for figuring out what shared libraries are in use, but the catch is that everything which refers to addresses (symbol tables and breakpoints at least) needs to be relocated for both shared libraries and the main executable. At least using the standard mechanism this can only be done once the program has been run (or the core file has been read).
Windows 95 and NT use the PE (Portable Executable) format for their executables. PE is basically COFF with additional headers.
While BFD includes special PE support, gdb needs only the basic COFF reader.
The ELF format came with System V Release 4 (SVR4) Unix. ELF is similar to COFF in being organized into a number of sections, but it removes many of COFF's limitations. Debugging info may be either stabs encapsulated in ELF sections, or more commonly these days, DWARF.
The basic ELF reader is in elfread.c.
SOM is HP's object file and debug format (not to be confused with IBM's SOM, which is a cross-language ABI).
The SOM reader is in somread.c.
This section describes characteristics of debugging information that are independent of the object file format.
stabs started out as special symbols within the a.out
format. Since then, it has been encapsulated into other file
formats, such as COFF and ELF.
While dbxread.c does some of the basic stab processing, including for encapsulated versions, stabsread.c does the real work.
The basic COFF definition includes debugging information. The level of support is minimal and non-extensible, and is not often used.
ECOFF includes a definition of a special debug format.
The file mdebugread.c implements reading for this format.
DWARF 2 is an improved but incompatible version of DWARF 1.
The DWARF 2 reader is in dwarf2read.c.
Compressed DWARF 2 is not technically a separate debugging format, but
merely DWARF 2 debug information that has been compressed. In this
format, every object-file section holding DWARF 2 debugging
information is compressed and prepended with a header. (The section
is also typically renamed, so a section called .debug_info in a
DWARF 2 binary would be called .zdebug_info in a compressed
DWARF 2 binary.) The header is 12 bytes long:
The same reader is used for both compressed an normal DWARF 2 info.
Section decompression is done in zlib_decompress_section in
dwarf2read.c.
DWARF 3 is an improved version of DWARF 2.
Like COFF, the SOM definition includes debugging information.
If you are using an existing object file format (a.out, COFF, ELF, etc),
there is probably little to be done.
If you need to add a new object file format, you must first add it to BFD. This is beyond the scope of this document.
You must then arrange for the BFD code to provide access to the debugging symbols. Generally gdb will have to call swapping routines from BFD and a few other BFD internal routines to locate the debugging information. As much as possible, gdb should not depend on the BFD internal data structures.
For some targets (e.g., COFF), there is a special transfer vector used to call swapping routines, since the external data structures on various platforms have different sizes and layouts. Specialized routines that will only ever be implemented by one object file format may be called directly. This interface should be described in a file bfd/libxyz.h, which is included by gdb.
Most memory associated with a loaded symbol file is stored on
its objfile_obstack. This includes symbols, types,
namespace data, and other information produced by the symbol readers.
Because this data lives on the objfile's obstack, it is automatically released when the objfile is unloaded or reloaded. Therefore one objfile must not reference symbol or type data from another objfile; they could be unloaded at different times.
User convenience variables, et cetera, have associated types. Normally these types live in the associated objfile. However, when the objfile is unloaded, those types are deep copied to global memory, so that the values of the user variables and history items are not lost.
gdb's language support is mainly driven by the symbol reader, although it is possible for the user to set the source language manually.
gdb chooses the source language by looking at the extension of the file recorded in the debug info; .c means C, .f means Fortran, etc. It may also use a special-purpose language identifier if the debug format supports it, like with DWARF.
To add other languages to gdb's expression parser, follow the following steps:
union exp_element list are in
parse.c.
Since we can't depend upon everyone having Bison, and YACC produces parsers that define a bunch of global names, the following lines must be included at the top of the YACC parser, to prevent the various parsers from defining the same global names:
#define yyparse lang_parse
#define yylex lang_lex
#define yyerror lang_error
#define yylval lang_lval
#define yychar lang_char
#define yydebug lang_debug
#define yypact lang_pact
#define yyr1 lang_r1
#define yyr2 lang_r2
#define yydef lang_def
#define yychk lang_chk
#define yypgo lang_pgo
#define yyact lang_act
#define yyexca lang_exca
#define yyerrflag lang_errflag
#define yynerrs lang_nerrs
At the bottom of your parser, define a struct language_defn and
initialize it with the right values for your language. Define an
initialize_lang routine and have it call
`add_language(lang_language_defn)' to tell the rest of gdb
that your language exists. You'll need some other supporting variables
and functions, which will be used via pointers from your
lang_language_defn. See the declaration of struct
language_defn in language.h, and the other *-exp.y files,
for more information.
evaluate_subexp function
defined in the file eval.c. Add cases
for new opcodes in two functions from parse.c:
prefixify_subexp and length_of_subexp. These compute
the number of exp_elements that a given operation takes up.
enum language in defs.h.
Update the routines in language.c so your language is included. These routines include type predicates and such, which (in some cases) are language dependent. If your language does not appear in the switch statement, an error is reported.
Also included in language.c is the code that updates the variable
current_language, and the routines that translate the
language_lang enumerated identifier into a printable
string.
Update the function _initialize_language to include your
language. This function picks the default language upon startup, so is
dependent upon which languages that gdb is built for.
Update allocate_symtab in symfile.c and/or symbol-reading
code so that the language of each symtab (source file) is set properly.
This is used to determine the language to use at each stack frame level.
Currently, the language is set based upon the extension of the source
file. If the language can be better inferred from the symbol
information, please set the language of the symtab in the symbol-reading
code.
Add helper code to print_subexp (in expprint.c) to handle any new
expression opcodes you have added to expression.h. Also, add the
printed representations of your operators to op_print_tab.
_parse() and lang_error in
parse_exp_1 (defined in parse.c).
HFILES and OBJS, otherwise your code may
not get linked in, or, worse yet, it may not get tarred into the
distribution!
With the advent of Autoconf, it's rarely necessary to have host definition machinery anymore. The following information is provided, mainly, as an historical reference.
gdb's host configuration support normally happens via Autoconf. New host-specific definitions should not be needed. Older hosts gdb still use the host-specific definitions and files listed below, but these mostly exist for historical reasons, and will eventually disappear.
Host configuration information included definitions for CC,
SYSV_DEFINE, XM_CFLAGS, XM_ADD_FILES,
XM_CLIBS, XM_CDEPS, etc.; see Makefile.in.
New host-only configurations do not need this file.
(Files named gdb/config/arch/xm-xyz.h were once used to define host-specific macros, but were no longer needed and have all been removed.)
There are some “generic” versions of routines that can be used by various systems.
When gdb is configured and compiled, various macros are
defined or left undefined, to control compilation based on the
attributes of the host system. While formerly they could be set in
host-specific header files, at present they can be changed only by
setting CFLAGS when building, or by editing the source code.
These macros and their meanings (or if the meaning is not documented here, then one of the source files where they are used is indicated) are:
INIT_FILENAMESIGWINCH_HANDLERSIGWINCH, you can define this to be the name
of a function to be called if SIGWINCH is received.
SIGWINCH_HANDLER_BODYSIGWINCH_HANDLER.
CRLF_SOURCE_FILES\r\n rather than \n as a
line terminator. This will cause source file listings to omit \r
characters when printing and it will allow \r\n line endings of files
which are “sourced” by gdb. It must be possible to open files in binary
mode using O_BINARY or, for fopen, "rb".
DEFAULT_PROMPT"(gdb) ").
DEV_TTY"/dev/tty".
ISATTYFOPEN_RBCC_HAS_LONG_LONGlong long. This is set
by the configure script.
PRINTF_HAS_LONG_LONGll. This is set by the
configure script.
LSEEK_NOT_LINEARlseek (n) does not necessarily move to byte number
n in the file. This is only used when reading source files. It
is normally faster to define CRLF_SOURCE_FILES when possible.
lintlint in some situations.
volatile__volatile__ or
/**/.
gdb's target architecture defines what sort of machine-language programs gdb can work with, and how it works with them.
The target architecture object is implemented as the C structure
struct gdbarch *. The structure, and its methods, are generated
using the Bourne shell script gdbarch.sh.
gdb provides a mechanism for handling variations in OS ABIs. An OS ABI variant may have influence over any number of variables in the target architecture definition. There are two major components in the OS ABI mechanism: sniffers and handlers.
A sniffer examines a file matching a BFD architecture/flavour pair
(the architecture may be wildcarded) in an attempt to determine the
OS ABI of that file. Sniffers with a wildcarded architecture are considered
to be generic, while sniffers for a specific architecture are
considered to be specific. A match from a specific sniffer
overrides a match from a generic sniffer. Multiple sniffers for an
architecture/flavour may exist, in order to differentiate between two
different operating systems which use the same basic file format. The
OS ABI framework provides a generic sniffer for ELF-format files which
examines the EI_OSABI field of the ELF header, as well as note
sections known to be used by several operating systems.
A handler is used to fine-tune the gdbarch structure for the
selected OS ABI. There may be only one handler for a given OS ABI
for each BFD architecture.
The following OS ABI variants are defined in defs.h:
GDB_OSABI_UNINITIALIZEDGDB_OSABI_UNKNOWNgdbarch
settings for the architecture will be used.
GDB_OSABI_SVR4GDB_OSABI_HURDGDB_OSABI_SOLARISGDB_OSABI_OSF1GDB_OSABI_LINUXGDB_OSABI_FREEBSD_AOUTa.out executable format.
GDB_OSABI_FREEBSD_ELFGDB_OSABI_NETBSD_AOUTa.out executable format.
GDB_OSABI_NETBSD_ELFGDB_OSABI_OPENBSD_ELFGDB_OSABI_WINCEGDB_OSABI_GO32GDB_OSABI_IRIXGDB_OSABI_INTERIXGDB_OSABI_HPUX_ELFGDB_OSABI_HPUX_SOMGDB_OSABI_QNXNTOGDB_OSABI_CYGWINGDB_OSABI_AIXHere are the functions that make up the OS ABI framework:
Return the name of the OS ABI corresponding to osabi.
Register the OS ABI handler specified by init_osabi for the architecture, machine type and OS ABI specified by arch, machine and osabi. In most cases, a value of zero for the machine type, which implies the architecture's default machine type, will suffice.
Register the OS ABI file sniffer specified by sniffer for the BFD architecture/flavour pair specified by arch and flavour. If arch is
bfd_arch_unknown, the sniffer is considered to be generic, and is allowed to examine flavour-flavoured files for any architecture.
Examine the file described by abfd to determine its OS ABI. The value
GDB_OSABI_UNKNOWNis returned if the OS ABI cannot be determined.
Invoke the OS ABI handler corresponding to osabi to fine-tune the
gdbarchstructure specified by gdbarch. If a handler corresponding to osabi has not been registered for gdbarch's architecture, a warning will be issued and the debugging session will continue with the defaults already established for gdbarch.
Helper routine for ELF file sniffers. Examine the file described by abfd and look at ABI tag note sections to determine the OS ABI from the note. This function should be called via
bfd_map_over_sections.
Each gdbarch is associated with a single bfd architecture,
via a bfd_arch_arch in the bfd_architecture
enumeration. The gdbarch is registered by a call to
register_gdbarch_init, usually from the file's
_initialize_filename routine, which will be automatically
called during gdb startup. The arguments are a bfd
architecture constant and an initialization function.
A gdb description for a new architecture, arch is created by
defining a global function _initialize_arch_tdep, by
convention in the source file arch-tdep.c. For example,
in the case of the OpenRISC 1000, this function is called
_initialize_or1k_tdep and is found in the file
or1k-tdep.c.
The resulting object files containing the implementation of the
_initialize_arch_tdep function are specified in the gdb
configure.tgt file, which includes a large case statement
pattern matching against the --target option of the
configure script. The new struct gdbarch is created
within the _initialize_arch_tdep function by calling
gdbarch_register:
void gdbarch_register (enum bfd_architecture architecture,
gdbarch_init_ftype *init_func,
gdbarch_dump_tdep_ftype *tdep_dump_func);
The architecture will identify the unique bfd to be
associated with this gdbarch. The init_func funciton is
called to create and return the new struct gdbarch. The
tdep_dump_func function will dump the target specific details
associated with this architecture.
For example the function _initialize_or1k_tdep creates its
architecture for 32-bit OpenRISC 1000 architectures by calling:
gdbarch_register (bfd_arch_or32, or1k_gdbarch_init, or1k_dump_tdep);
The initialization function has this prototype:
static struct gdbarch *
arch_gdbarch_init (struct gdbarch_info info,
struct gdbarch_list *arches)
The info argument contains parameters used to select the correct
architecture, and arches is a list of architectures which
have already been created with the same bfd_arch_arch
value.
The initialization function should first make sure that info
is acceptable, and return NULL if it is not. Then, it should
search through arches for an exact match to info, and
return one if found. Lastly, if no exact match was found, it should
create a new architecture based on info and return it.
The lookup is done using gdbarch_list_lookup_by_info. It is
passed the list of existing architectures, arches, and the
struct gdbarch_info, info, and returns the first matching
architecture it finds, or NULL if none are found. If an
architecture is found it can be returned as the result from the
initialization function, otherwise a new struct gdbach will need
to be created.
The struct gdbarch_info has the following components:
struct gdbarch_info
{
const struct bfd_arch_info *bfd_arch_info;
int byte_order;
bfd *abfd;
struct gdbarch_tdep_info *tdep_info;
enum gdb_osabi osabi;
const struct target_desc *target_desc;
};
The bfd_arch_info member holds the key details about the
architecture. The byte_order member is a value in an
enumeration indicating the endianism. The abfd member is a
pointer to the full bfd, the tdep_info member is
additional custom target specific information, osabi identifies
which (if any) of a number of operating specific ABIs are used by this
architecture and the target_desc member is a set of name-value
pairs with information about register usage in this target.
When the struct gdbarch initialization function is called, not
all the fields are provided—only those which can be deduced from the
bfd. The struct gdbarch_info, info is used as a
look-up key with the list of existing architectures, arches to
see if a suitable architecture already exists. The tdep_info,
osabi and target_desc fields may be added before this
lookup to refine the search.
Only information in info should be used to choose the new
architecture. Historically, info could be sparse, and
defaults would be collected from the first element on arches.
However, gdb now fills in info more thoroughly,
so new gdbarch initialization functions should not take
defaults from arches.
If no architecture is found, then a new architecture must be created,
by calling gdbarch_alloc using the supplied struct gdbarch_info and any additional custom target specific
information in a struct gdbarch_tdep. The prototype for
gdbarch_alloc is:
struct gdbarch *gdbarch_alloc (const struct gdbarch_info *info,
struct gdbarch_tdep *tdep);
The newly created struct gdbarch must then be populated. Although there are default values, in most cases they are not what is required.
For each element, X, there is are a pair of corresponding accessor
functions, one to set the value of that element,
set_gdbarch_X, the second to either get the value of an
element (if it is a variable) or to apply the element (if it is a
function), gdbarch_X. Note that both accessor functions
take a pointer to the struct gdbarch as first
argument. Populating the new gdbarch should use the
set_gdbarch functions.
The following sections identify the main elements that should be set in this way. This is not the complete list, but represents the functions and elements that must commonly be specified for a new architecture. Many of the functions and variables are described in the header file gdbarch.h.
This is the main work in defining a new architecture. Implementing the
set of functions to populate the struct gdbarch.
struct gdbarch_tdep is not defined within gdb—it is up
to the user to define this struct if it is needed to hold custom target
information that is not covered by the standard struct gdbarch. For example with the OpenRISC 1000 architecture it is used to
hold the number of matchpoints available in the target (along with other
information).
If there is no additional target specific information, it can be set to
NULL.
gdb's model of the target machine is rather simple. gdb assumes the machine includes a bank of registers and a block of memory. Each register may have a different size.
gdb does not have a magical way to match up with the
compiler's idea of which registers are which; however, it is critical
that they do match up accurately. The only way to make this work is
to get accurate information about the order that the compiler uses,
and to reflect that in the gdbarch_register_name and related functions.
gdb can handle big-endian, little-endian, and bi-endian architectures.
On almost all 32-bit architectures, the representation of a pointer is indistinguishable from the representation of some fixed-length number whose value is the byte address of the object pointed to. On such machines, the words “pointer” and “address” can be used interchangeably. However, architectures with smaller word sizes are often cramped for address space, so they may choose a pointer representation that breaks this identity, and allows a larger code address space.
For example, the Renesas D10V is a 16-bit VLIW processor whose instructions are 32 bits long3. If the D10V used ordinary byte addresses to refer to code locations, then the processor would only be able to address 64kb of instructions. However, since instructions must be aligned on four-byte boundaries, the low two bits of any valid instruction's byte address are always zero—byte addresses waste two bits. So instead of byte addresses, the D10V uses word addresses—byte addresses shifted right two bits—to refer to code. Thus, the D10V can use 16-bit words to address 256kb of code space.
However, this means that code pointers and data pointers have different
forms on the D10V. The 16-bit word 0xC020 refers to byte address
0xC020 when used as a data address, but refers to byte address
0x30080 when used as a code address.
(The D10V also uses separate code and data address spaces, which also affects the correspondence between pointers and addresses, but we're going to ignore that here; this example is already too long.)
To cope with architectures like this—the D10V is not the only
one!—gdb tries to distinguish between addresses, which are
byte numbers, and pointers, which are the target's representation
of an address of a particular type of data. In the example above,
0xC020 is the pointer, which refers to one of the addresses
0xC020 or 0x30080, depending on the type imposed upon it.
gdb provides functions for turning a pointer into an address
and vice versa, in the appropriate way for the current architecture.
Unfortunately, since addresses and pointers are identical on almost all processors, this distinction tends to bit-rot pretty quickly. Thus, each time you port gdb to an architecture which does distinguish between pointers and addresses, you'll probably need to clean up some architecture-independent code.
Here are functions which convert between pointers and addresses:
Treat the bytes at buf as a pointer or reference of type type, and return the address it represents, in a manner appropriate for the current architecture. This yields an address gdb can use to read target memory, disassemble, etc. Note that buf refers to a buffer in gdb's memory, not the inferior's.
For example, if the current architecture is the Intel x86, this function extracts a little-endian integer of the appropriate length from buf and returns it. However, if the current architecture is the D10V, this function will return a 16-bit integer extracted from buf, multiplied by four if type is a pointer to a function.
If type is not a pointer or reference type, then this function will signal an internal error.
Store the address addr in buf, in the proper format for a pointer of type type in the current architecture. Note that buf refers to a buffer in gdb's memory, not the inferior's.
For example, if the current architecture is the Intel x86, this function stores addr unmodified as a little-endian integer of the appropriate length in buf. However, if the current architecture is the D10V, this function divides addr by four if type is a pointer to a function, and then stores it in buf.
If type is not a pointer or reference type, then this function will signal an internal error.
Assuming that val is a pointer, return the address it represents, as appropriate for the current architecture.
This function actually works on integral values, as well as pointers. For pointers, it performs architecture-specific conversions as described above for
extract_typed_address.
Create and return a value representing a pointer of type type to the address addr, as appropriate for the current architecture. This function performs architecture-specific conversions as described above for
store_typed_address.
Here are two functions which architectures can define to indicate the relationship between pointers and addresses. These have default definitions, appropriate for architectures on which all pointers are simple unsigned byte addresses.
Assume that buf holds a pointer of type type, in the appropriate format for the current architecture. Return the byte address the pointer refers to.
This function may safely assume that type is either a pointer or a C++ reference type.
Store in buf a pointer of type type representing the address addr, in the appropriate format for the current architecture.
This function may safely assume that type is either a pointer or a C++ reference type.
Sometimes information about different kinds of addresses is available
via the debug information. For example, some programming environments
define addresses of several different sizes. If the debug information
distinguishes these kinds of address classes through either the size
info (e.g, DW_AT_byte_size in DWARF 2) or through an explicit
address class attribute (e.g, DW_AT_address_class in DWARF 2), the
following macros should be defined in order to disambiguate these
types within gdb as well as provide the added information to
a gdb user when printing type expressions.
Returns the type flags needed to construct a pointer type whose size is byte_size and whose address class is dwarf2_addr_class. This function is normally called from within a symbol reader. See dwarf2read.c.
Given the type flags representing an address class qualifier, return its name.
Given an address qualifier name, set the
intreferenced by type_flags_ptr to the type flags for that address class qualifier.
Since the need for address classes is rather rare, none of the address class functions are defined by default. Predicate functions are provided to detect when they are defined.
Consider a hypothetical architecture in which addresses are normally
32-bits wide, but 16-bit addresses are also supported. Furthermore,
suppose that the DWARF 2 information for this architecture simply
uses a DW_AT_byte_size value of 2 to indicate the use of one
of these "short" pointers. The following functions could be defined
to implement the address class functions:
somearch_address_class_type_flags (int byte_size,
int dwarf2_addr_class)
{
if (byte_size == 2)
return TYPE_FLAG_ADDRESS_CLASS_1;
else
return 0;
}
static char *
somearch_address_class_type_flags_to_name (int type_flags)
{
if (type_flags & TYPE_FLAG_ADDRESS_CLASS_1)
return "short";
else
return NULL;
}
int
somearch_address_class_name_to_type_flags (char *name,
int *type_flags_ptr)
{
if (strcmp (name, "short") == 0)
{
*type_flags_ptr = TYPE_FLAG_ADDRESS_CLASS_1;
return 1;
}
else
return 0;
}
The qualifier @short is used in gdb's type expressions
to indicate the presence of one of these “short” pointers. For
example if the debug information indicates that short_ptr_var is
one of these short pointers, gdb might show the following
behavior:
(gdb) ptype short_ptr_var
type = int * @short
gdb considers registers to be a set with members numbered linearly from 0 upwards. The first part of that set corresponds to real physical registers, the second part to any pseudo-registers. Pseudo-registers have no independent physical existence, but are useful representations of information within the architecture. For example the OpenRISC 1000 architecture has up to 32 general purpose registers, which are typically represented as 32-bit (or 64-bit) integers. However the GPRs are also used as operands to the floating point operations, and it could be convenient to define a set of pseudo-registers, to show the GPRs represented as floating point values.
For any architecture, the implementer will decide on a mapping from hardware to gdb register numbers. The registers corresponding to real hardware are referred to as raw registers, the remaining registers are pseudo-registers. The total register set (raw and pseudo) is called the cooked register set.
These struct gdbarch functions and variables specify the number
and type of registers in the architecture.
Read or write the program counter. The default value of both functions is
NULL(no function available). If the program counter is just an ordinary register, it can be specified instruct gdbarchinstead (seepc_regnumbelow) and it will be read or written using the standard routines to access registers. This function need only be specified if the program counter is not an ordinary register.Any register information can be obtained using the supplied register cache, regcache. See Register Caching.
These functions should be defined if there are any pseudo-registers. The default value is
NULL. regnum is the number of the register to read or write (which will be a cooked register number) and buf is the buffer where the value read will be placed, or from which the value to be written will be taken. The value in the buffer may be converted to or from a signed or unsigned integral value using one of the utility functions (see Using Different Register and Memory Data Representations).The access should be for the specified architecture, gdbarch. Any register information can be obtained using the supplied register cache, regcache. See Register Caching.
This specifies the register holding the stack pointer, which may be a raw or pseudo-register. It defaults to -1 (not defined), but it is an error for it not to be defined.
The value of the stack pointer register can be accessed withing gdb as the variable $sp.
This specifies the register holding the program counter, which may be a raw or pseudo-register. It defaults to -1 (not defined). If
pc_regnumis not defined, then the functionsread_pcandwrite_pc(see above) must be defined.The value of the program counter (whether defined as a register, or through
read_pcandwrite_pc) can be accessed withing gdb as the variable $pc.
This specifies the register holding the processor status (often called the status register), which may be a raw or pseudo-register. It defaults to -1 (not defined).
If defined, the value of this register can be accessed withing gdb as the variable $ps.
This specifies the first floating point register. It defaults to 0.
fp0_regnumis not needed unless the target offers support for floating point.
These functions return information about registers.
This function should convert a register number (raw or pseudo) to a register name (as a C
const char *). This is used both to determine the name of a register for output and to work out the meaning of any register names used as input. The function may also returnNULL, to indicate that regnum is not a valid register.For example with the OpenRISC 1000, gdb registers 0-31 are the General Purpose Registers, register 32 is the program counter and register 33 is the supervision register (i.e. the processor status register), which map to the strings
"gpr00"through"gpr31","pc"and"sr"respectively. This means that the gdb command print $gpr5 should print the value of the OR1K general purpose register 54.The default value for this function is
NULL, meaning undefined. It should always be defined.The access should be for the specified architecture, gdbarch.
Given a register number, this function identifies the type of data it may be holding, specified as a
struct type. gdb allows creation of arbitrary types, but a number of built in types are provided (builtin_type_void,builtin_type_int32etc), together with functions to derive types from these.Typically the program counter will have a type of “pointer to function” (it points to code), the frame pointer and stack pointer will have types of “pointer to void” (they point to data on the stack) and all other integer registers will have a type of 32-bit integer or 64-bit integer.
This information guides the formatting when displaying register information. The default value is
NULLmeaning no information is available to guide formatting when displaying registers.
Define this function to print out one or all of the registers for the gdb info registers command. The default value is the function
default_print_registers_info, which uses the register type information (seeregister_typeabove) to determine how each register should be printed. Define a custom version of this function for fuller control over how the registers are displayed.The access should be for the specified architecture, gdbarch, with output to the the file specified by the User Interface Independent Output file handle, file (see UI-Independent Output—the
ui_outFunctions).The registers should show their values in the frame specified by frame. If regnum is -1 and all is zero, then all the “significant” registers should be shown (the implementer should decide which registers are “significant”). Otherwise only the value of the register specified by regnum should be output. If regnum is -1 and all is non-zero (true), then the value of all registers should be shown.
By default
default_print_registers_infoprints one register per line, and if all is zero omits floating-point registers.
Define this function to provide output about the floating point unit and registers for the gdb info float command respectively. The default value is
NULL(not defined), meaning no information will be provided.The gdbarch and file and frame arguments have the same meaning as in the
print_registers_infofunction above. The string args contains any supplementary arguments to the info float command.Define this function if the target supports floating point operations.
Define this function to provide output about the vector unit and registers for the gdb info vector command respectively. The default value is
NULL(not defined), meaning no information will be provided.The gdbarch, file and frame arguments have the same meaning as in the
print_registers_infofunction above. The string args contains any supplementary arguments to the info vector command.Define this function if the target supports vector operations.
gdb groups registers into different categories (general, vector, floating point etc). This function, given a register, regnum, and group, group, returns 1 (true) if the register is in the group and 0 (false) otherwise.
The information should be for the specified architecture, gdbarch
The default value is the function
default_register_reggroup_pwhich will do a reasonable job based on the type of the register (see the functionregister_typeabove), with groups for general purpose registers, floating point registers, vector registers and raw (i.e not pseudo) registers.
Some architectures have different representations of data objects, depending whether the object is held in a register or memory. For example:
long double data type occupies 96 bits in memory but only 80
bits when stored in a register.
In general, the register representation of a data type is determined by the architecture, or gdb's interface to the architecture, while the memory representation is determined by the Application Binary Interface.
For almost all data types on almost all architectures, the two
representations are identical, and no special handling is needed.
However, they do occasionally differ. An architecture may define the
following struct gdbarch functions to request conversions
between the register and memory representations of a data type:
Return non-zero (true) if the representation of a data value stored in this register may be different to the representation of that same data value when stored in memory. The default value is
NULL(undefined).If this function is defined and returns non-zero, the
struct gdbarchfunctionsgdbarch_register_to_valueandgdbarch_value_to_register(see below) should be used to perform any necessary conversion.If defined, this function should return zero for the register's native type, when no conversion is necessary.
Convert the value of register number reg to a data object of type type. The buffer at from holds the register's value in raw format; the converted value should be placed in the buffer at to.
Note:gdbarch_register_to_valueandgdbarch_value_to_registertake their reg and type arguments in different orders.
gdbarch_register_to_valueshould only be used with registers for which thegdbarch_convert_register_pfunction returns a non-zero value.
Convert a data value of type type to register number reg' raw format.
Note:gdbarch_register_to_valueandgdbarch_value_to_registertake their reg and type arguments in different orders.
gdbarch_value_to_registershould only be used with registers for which thegdbarch_convert_register_pfunction returns a non-zero value.
Caching of registers is used, so that the target does not need to be accessed and reanalyzed multiple times for each register in circumstances where the register value cannot have changed.
gdb provides struct regcache, associated with a
particular struct gdbarch to hold the cached values of the raw
registers. A set of functions is provided to access both the raw
registers (with raw in their name) and the full set of cooked
registers (with cooked in their name). Functions are provided
to ensure the register cache is kept synchronized with the values of
the actual registers in the target.
Accessing registers through the struct regcache routines will
ensure that the appropriate struct gdbarch functions are called
when necessary to access the underlying target architecture. In general
users should use the cooked functions, since these will map to the
raw functions automatically as appropriate.
The two key functions are regcache_cooked_read and
regcache_cooked_write which read or write a register from or to
a byte buffer (type gdb_byte *). For convenience the wrapper
functions regcache_cooked_read_signed,
regcache_cooked_read_unsigned,
regcache_cooked_write_signed and
regcache_cooked_write_unsigned are provided, which read or
write the value using the buffer and convert to or from an integral
value as appropriate.
gdb needs to understand the stack on which local (automatic) variables are stored. The area of the stack containing all the local variables for a function invocation is known as the stack frame for that function (or colloquially just as the frame). In turn the function that called the function will have its stack frame, and so on back through the chain of functions that have been called.
Almost all architectures have one register dedicated to point to the end of the stack (the stack pointer). Many have a second register which points to the start of the currently active stack frame (the frame pointer). The specific arrangements for an architecture are a key part of the ABI.
A diagram helps to explain this. Here is a simple program to compute factorials:
#include <stdio.h>
int fact (int n)
{
if (0 == n)
{
return 1;
}
else
{
return n * fact (n - 1);
}
}
main ()
{
int i;
for (i = 0; i < 10; i++)
{
int f = fact (i);
printf ("%d! = %d\n", i, f);
}
}
Consider the state of the stack when the code reaches line 6 after the
main program has called fact (3). The chain of function
calls will be main (), fact (3), fact (2), fact (1) and fact (0).
In this illustration the stack is falling (as used for example by the OpenRISC 1000 ABI). The stack pointer (SP) is at the end of the stack (lowest address) and the frame pointer (FP) is at the highest address in the current stack frame. The following diagram shows how the stack looks.
In each stack frame, offset 0 from the stack pointer is the frame
pointer of the previous frame and offset 4 (this is illustrating a
32-bit architecture) from the stack pointer is the return address.
Local variables are indexed from the frame pointer, with negative
indexes. In the function fact, offset -4 from the frame
pointer is the argument n. In the main function, offset
-4 from the frame pointer is the local variable i and offset -8
from the frame pointer is the local variable f5.
It is very easy to get confused when examining stacks. gdb
has terminology it uses rigorously throughout. The stack frame of the
function currently executing, or where execution stopped is numbered
zero. In this example frame #0 is the stack frame of the call to
fact (0). The stack frame of its calling function
(fact (1) in this case) is numbered #1 and so on back
through the chain of calls.
The main gdb data structure describing frames is
struct frame_info. It is not used directly, but only via
its accessor functions. frame_info includes information about
the registers in the frame and a pointer to the code of the function
with which the frame is associated. The entire stack is represented as
a linked list of frame_info structs.
It is easy to get confused when referencing stack frames. gdb uses some precise terminology.
So in the example in the previous section (see All About Stack Frames), if THIS frame is #3 (the call to
fact (3)), the NEXT frame is frame #2 (the call to
fact (2)) and the PREVIOUS frame is frame #4 (the call to
main ()).
The innermost frame is the frame of the current executing
function, or where the program stopped, in this example, in the middle
of the call to fact (0)). It is always numbered frame #0.
The base of a frame is the address immediately before the start of the NEXT frame. For a stack which grows down in memory (a falling stack) this will be the lowest address and for a stack which grows up in memory (a rising stack) this will be the highest address in the frame.
gdb functions to analyze the stack are typically given a pointer to the NEXT frame to determine information about THIS frame. Information about THIS frame includes data on where the registers of the PREVIOUS frame are stored in this stack frame. In this example the frame pointer of the PREVIOUS frame is stored at offset 0 from the stack pointer of THIS frame.
The process whereby a function is given a pointer to the NEXT frame to work out information about THIS frame is referred to as unwinding. The gdb functions involved in this typically include unwind in their name.
The process of analyzing a target to determine the information that should go in struct frame_info is called sniffing. The functions that carry this out are called sniffers and typically include sniffer in their name. More than one sniffer may be required to extract all the information for a particular frame.
Because so many functions work using the NEXT frame, there is an issue about addressing the innermost frame—it has no NEXT frame. To solve this gdb creates a dummy frame #-1, known as the sentinel frame.
All the frame sniffing functions typically examine the code at the start of the corresponding function, to determine the state of registers. The ABI will save old values and set new values of key registers at the start of each function in what is known as the function prologue.
For any particular stack frame this data does not change, so all the standard unwinding functions, in addition to receiving a pointer to the NEXT frame as their first argument, receive a pointer to a prologue cache as their second argument. This can be used to store values associated with a particular frame, for reuse on subsequent calls involving the same frame.
It is up to the user to define the structure used (it is a
void * pointer) and arrange allocation and deallocation of
storage. However for general use, gdb provides
struct trad_frame_cache, with a set of accessor
routines. This structure holds the stack and code address of
THIS frame, the base address of the frame, a pointer to the
struct frame_info for the NEXT frame and details of
where the registers of the PREVIOUS frame may be found in THIS
frame.
Typically the first time any sniffer function is called with NEXT
frame, the prologue sniffer for THIS frame will be NULL. The
sniffer will analyze the frame, allocate a prologue cache structure
and populate it. Subsequent calls using the same NEXT frame will
pass in this prologue cache, so the data can be returned with no
additional analysis.
These struct gdbarch functions and variable should be defined
to provide analysis of the stack frame and allow it to be adjusted as
required.
The prologue of a function is the code at the beginning of the function which sets up the stack frame, saves the return address etc. The code representing the behavior of the function starts after the prologue.
This function skips past the prologue of a function if the program counter, pc, is within the prologue of a function. The result is the program counter immediately after the prologue. With modern optimizing compilers, this may be a far from trivial exercise. However the required information may be within the binary as DWARF2 debugging information, making the job much easier.
The default value is
NULL(not defined). This function should always be provided, but can take advantage of DWARF2 debugging information, if that is available.
Given two frame or stack pointers, return non-zero (true) if the first represents the inner stack frame and 0 (false) otherwise. This is used to determine whether the target has a stack which grows up in memory (rising stack) or grows down in memory (falling stack). See All About Stack Frames, for an explanation of inner frames.
The default value of this function is
NULLand it should always be defined. However for almost all architectures one of the built-in functions can be used:core_addr_lessthan(for stacks growing down in memory) orcore_addr_greaterthan(for stacks growing up in memory).
The architecture may have constraints on how its frames are aligned. For example the OpenRISC 1000 ABI requires stack frames to be double-word aligned, but 32-bit versions of the architecture allocate single-word values to the stack. Thus extra padding may be needed at the end of a stack frame.
Given a proposed address for the stack pointer, this function returns a suitably aligned address (by expanding the stack frame).
The default value is
NULL(undefined). This function should be defined for any architecture where it is possible the stack could become misaligned. The utility functionsalign_down(for falling stacks) andalign_up(for rising stacks) will facilitate the implementation of this function.
Some ABIs reserve space beyond the end of the stack for use by leaf functions without prologue or epilogue or by exception handlers (for example the OpenRISC 1000).
This is known as a red zone (AMD terminology). The amd64 (nee x86-64) ABI documentation refers to the red zone when describing this scratch area.
The default value is 0. Set this field if the architecture has such a red zone. The value must be aligned as required by the ABI (see
frame_alignabove for an explanation of stack frame alignment).
These functions provide access to key registers and arguments in the stack frame.
This function is given a pointer to the NEXT stack frame (see All About Stack Frames, for how frames are represented) and returns the value of the program counter in the PREVIOUS frame (i.e. the frame of the function that called THIS one). This is commonly referred to as the return address.
The implementation, which must be frame agnostic (work with any frame), is typically no more than:
ULONGEST pc; pc = frame_unwind_register_unsigned (next_frame, ARCH_PC_REGNUM); return gdbarch_addr_bits_remove (gdbarch, pc);
This function is given a pointer to the NEXT stack frame (see All About Stack Frames for how frames are represented) and returns the value of the stack pointer in the PREVIOUS frame (i.e. the frame of the function that called THIS one).
The implementation, which must be frame agnostic (work with any frame), is typically no more than:
ULONGEST sp; sp = frame_unwind_register_unsigned (next_frame, ARCH_SP_REGNUM); return gdbarch_addr_bits_remove (gdbarch, sp);
This function is given a pointer to THIS stack frame (see All About Stack Frames for how frames are represented), and returns the number of arguments that are being passed, or -1 if not known.
The default value is
NULL(undefined), in which case the number of arguments passed on any stack frame is always unknown. For many architectures this will be a suitable default.
When a program stops, gdb needs to construct the chain of
struct frame_info representing the state of the stack using
appropriate sniffers.
Each architecture requires appropriate sniffers, but they do not form
entries in struct gdbarch, since more than one sniffer may
be required and a sniffer may be suitable for more than one
struct gdbarch. Instead sniffers are associated with
architectures using the following functions.
frame_unwind_append_sniffer is used to add a new sniffer to
analyze THIS frame when given a pointer to the NEXT frame.
frame_base_append_sniffer is used to add a new sniffer
which can determine information about the base of a stack frame.
frame_base_set_default is used to specify the default base
sniffer.
These functions all take a reference to struct gdbarch, so
they are associated with a specific architecture. They are usually
called in the gdbarch initialization function, after the
gdbarch struct has been set up. Unless a default has been set, the
most recently appended sniffer will be tried first.
The main frame unwinding sniffer (as set by
frame_unwind_append_sniffer) returns a structure specifying
a set of sniffing functions:
struct frame_unwind
{
enum frame_type type;
frame_this_id_ftype *this_id;
frame_prev_register_ftype *prev_register;
const struct frame_data *unwind_data;
frame_sniffer_ftype *sniffer;
frame_prev_pc_ftype *prev_pc;
frame_dealloc_cache_ftype *dealloc_cache;
};
The type field indicates the type of frame this sniffer can
handle: normal, dummy (see Functions Creating Dummy Frames), signal handler or sentinel. Signal
handlers sometimes have their own simplified stack structure for
efficiency, so may need their own handlers.
The unwind_data field holds additional information which may be
relevant to particular types of frame. For example it may hold
additional information for signal handler frames.
The remaining fields define functions that yield different types of
information when given a pointer to the NEXT stack frame. Not all
functions need be provided. If an entry is NULL, the next sniffer will
be tried instead.
this_id determines the stack pointer and function (code
entry point) for THIS stack frame.
prev_register determines where the values of registers for
the PREVIOUS stack frame are stored in THIS stack frame.
sniffer takes a look at THIS frame's registers to
determine if this is the appropriate unwinder.
prev_pc determines the program counter for THIS
frame. Only needed if the program counter is not an ordinary register
(see Functions and Variables Specifying the Register Architecture).
dealloc_cache frees any additional memory associated with
the prologue cache for this frame (see Prologue Caches).
In general it is only the this_id and prev_register
fields that need be defined for custom sniffers.
The frame base sniffer is much simpler. It is a struct frame_base, which refers to the corresponding frame_unwind
struct and whose fields refer to functions yielding various addresses
within the frame.
struct frame_base
{
const struct frame_unwind *unwind;
frame_this_base_ftype *this_base;
frame_this_locals_ftype *this_locals;
frame_this_args_ftype *this_args;
};
All the functions referred to take a pointer to the NEXT frame as
argument. The function referred to by this_base returns the
base address of THIS frame, the function referred to by
this_locals returns the base address of local variables in THIS
frame and the function referred to by this_args returns the
base address of the function arguments in this frame.
As described above, the base address of a frame is the address immediately before the start of the NEXT frame. For a falling stack, this is the lowest address in the frame and for a rising stack it is the highest address in the frame. For most architectures the same address is also the base address for local variables and arguments, in which case the same function can be used for all three entries6.
gdb can call functions in the target code (for example by using the call or print commands). These functions may be breakpointed, and it is essential that if a function does hit a breakpoint, commands like backtrace work correctly.
This is achieved by making the stack look as though the function had been called from the point where gdb had previously stopped. This requires that gdb can set up stack frames appropriate for such function calls.
The following functions provide the functionality to set up such dummy stack frames.
This function sets up a dummy stack frame for the function about to be called.
push_dummy_callis given the arguments to be passed and must copy them into registers or push them on to the stack as appropriate for the ABI.function is a pointer to the function that will be called and regcache the register cache from which values should be obtained. bp_addr is the address to which the function should return (which is breakpointed, so gdb can regain control, hence the name). nargs is the number of arguments to pass and args an array containing the argument values. struct_return is non-zero (true) if the function returns a structure, and if so struct_addr is the address in which the structure should be returned.
After calling this function, gdb will pass control to the target at the address of the function, which will find the stack and registers set up just as expected.
The default value of this function is
NULL(undefined). If the function is not defined, then gdb will not allow the user to call functions within the target being debugged.
This is the inverse of
push_dummy_callwhich restores the stack pointer and program counter after a call to evaluate a function using a dummy stack frame. The result is astruct frame_id, which contains the value of the stack pointer and program counter to be used.The NEXT frame pointer is provided as argument, next_frame. THIS frame is the frame of the dummy function, which can be unwound, to yield the required stack pointer and program counter from the PREVIOUS frame.
The default value is
NULL(undefined). Ifpush_dummy_callis defined, then this function should also be defined.
If this function is not defined (its default value is
NULL), a dummy call will use the entry point of the currently loaded code on the target as its return address. A temporary breakpoint will be set there, so the location must be writable and have room for a breakpoint.It is possible that this default is not suitable. It might not be writable (in ROM possibly), or the ABI might require code to be executed on return from a call to unwind the stack before the breakpoint is encountered.
If either of these is the case, then push_dummy_code should be defined to push an instruction sequence onto the end of the stack to which the dummy call should return.
The arguments are essentially the same as those to
push_dummy_call. However the function is provided with the type of the function result, value_type, bp_addr is used to return a value (the address at which the breakpoint instruction should be inserted) and real pc is used to specify the resume address when starting the call sequence. The function should return the updated innermost stack address.Note: This does require that code in the stack can be executed. Some Harvard architectures may not allow this.
The prerequisite for adding core file support in gdb is to have core file support in BFD.
Once BFD support is available, writing the apropriate
regset_from_core_section architecture function should be all
that is needed in order to add support for core files in gdb.
This section describes other functions and values in gdbarch,
together with some useful macros, that you can use to define the
target architecture.
CORE_ADDR gdbarch_addr_bits_remove (gdbarch, addr)For example, the two low-order bits of the PC on the Hewlett-Packard PA
2.0 architecture contain the privilege level of the corresponding
instruction. Since instructions must always be aligned on four-byte
boundaries, the processor masks out these bits to generate the actual
address of the instruction. gdbarch_addr_bits_remove would then for
example look like that:
arch_addr_bits_remove (CORE_ADDR addr)
{
return (addr &= ~0x3);
}
int address_class_name_to_type_flags (gdbarch, name, type_flags_ptr)int
referenced by type_flags_ptr to the mask representing the qualifier
and return 1. If name is not a valid address class qualifier name,
return 0.
The value for type_flags_ptr should be one of
TYPE_FLAG_ADDRESS_CLASS_1, TYPE_FLAG_ADDRESS_CLASS_2, or
possibly some combination of these values or'd together.
See Address Classes.
int address_class_name_to_type_flags_p (gdbarch)address_class_name_to_type_flags
has been defined.
int gdbarch_address_class_type_flags (gdbarch, byte_size, dwarf2_addr_class)DW_AT_address_class value, return the type flags
used by gdb to represent this address class. The value
returned should be one of TYPE_FLAG_ADDRESS_CLASS_1,
TYPE_FLAG_ADDRESS_CLASS_2, or possibly some combination of these
values or'd together.
See Address Classes.
int gdbarch_address_class_type_flags_p (gdbarch)gdbarch_address_class_type_flags_p has
been defined.
const char *gdbarch_address_class_type_flags_to_name (gdbarch, type_flags)int gdbarch_address_class_type_flags_to_name_p (gdbarch)gdbarch_address_class_type_flags_to_name has been defined.
See Address Classes.
void gdbarch_address_to_pointer (gdbarch, type, buf, addr)int gdbarch_believe_pcc_promotion (gdbarch)short or char
parameter to an int, but still reports the parameter as its
original type, rather than the promoted type.
gdbarch_bits_big_endian (gdbarch)set_gdbarch_bits_big_endian (gdbarch, bits_big_endian)BREAKPOINTBREAKPOINT has been deprecated in favor of
gdbarch_breakpoint_from_pc.
BIG_BREAKPOINTLITTLE_BREAKPOINTBIG_BREAKPOINT and LITTLE_BREAKPOINT have been deprecated in
favor of gdbarch_breakpoint_from_pc.
const gdb_byte *gdbarch_breakpoint_from_pc (gdbarch, pcptr, lenptr)*lenptr, and adjusts the program
counter (if necessary) to point to the actual memory location where the
breakpoint should be inserted. May return NULL to indicate that
software breakpoints are not supported.
Although it is common to use a trap instruction for a breakpoint, it's not required; for instance, the bit pattern could be an invalid instruction. The breakpoint must be no longer than the shortest instruction of the architecture.
Provided breakpoint bytes can be also used by bp_loc_is_permanent to
detect permanent breakpoints. gdbarch_breakpoint_from_pc should return
an unchanged memory copy if it was called for a location with permanent
breakpoint as some architectures use breakpoint instructions containing
arbitrary parameter value.
Replaces all the other BREAKPOINT macros.
int gdbarch_memory_insert_breakpoint (gdbarch, bp_tgt)gdbarch_memory_remove_breakpoint (gdbarch, bp_tgt)default_memory_insert_breakpoint and
default_memory_remove_breakpoint respectively) have been
provided so that it is not necessary to set these for most
architectures. Architectures which may want to set
gdbarch_memory_insert_breakpoint and gdbarch_memory_remove_breakpoint will likely have instructions that are oddly sized or are not stored in a
conventional manner.
It may also be desirable (from an efficiency standpoint) to define
custom breakpoint insertion and removal routines if
gdbarch_breakpoint_from_pc needs to read the target's memory for some
reason.
CORE_ADDR gdbarch_adjust_breakpoint_address (gdbarch, bpaddr)The FR-V target (see frv-tdep.c) requires this method. The FR-V is a VLIW architecture in which a number of RISC-like instructions are grouped (packed) together into an aggregate instruction or instruction bundle. When the processor executes one of these bundles, the component instructions are executed in parallel.
In the course of optimization, the compiler may group instructions from distinct source statements into the same bundle. The line number information associated with one of the latter statements will likely refer to some instruction other than the first one in the bundle. So, if the user attempts to place a breakpoint on one of these latter statements, gdb must be careful to not place the break instruction on any instruction other than the first one in the bundle. (Remember though that the instructions within a bundle execute in parallel, so the first instruction is the instruction at the lowest address and has nothing to do with execution order.)
The FR-V's gdbarch_adjust_breakpoint_address method will adjust a
breakpoint's address by scanning backwards for the beginning of
the bundle, returning the address of the bundle.
Since the adjustment of a breakpoint may significantly alter a user's
expectation, gdb prints a warning when an adjusted breakpoint
is initially set and each time that that breakpoint is hit.
int gdbarch_call_dummy_location (gdbarch)This method has been replaced by gdbarch_push_dummy_code
(see gdbarch_push_dummy_code).
int gdbarch_cannot_fetch_register (gdbarch, regum)int gdbarch_cannot_store_register (gdbarch, regnum)int gdbarch_convert_register_p (gdbarch, regnum, struct type *type)int gdbarch_fp0_regnum (gdbarch)CORE_ADDR gdbarch_decr_pc_after_break (gdbarch)BREAKPOINT, though not always. For most targets this value will be 0.
DISABLE_UNSETTABLE_BREAK (addr)int gdbarch_dwarf2_reg_to_regnum (gdbarch, dwarf2_regnr)int gdbarch_ecoff_reg_to_regnum (gdbarch, ecoff_regnr)GCC_COMPILED_FLAG_SYMBOLGCC2_COMPILED_FLAG_SYMBOLgcc_compiled. and gcc2_compiled.,
respectively. (Currently only defined for the Delta 68.)
gdbarch_get_longjmp_targetlongjmp
will jump to, assuming that we have just stopped at a longjmp
breakpoint. It takes a CORE_ADDR * as argument, and stores the
target PC value through this pointer. It examines the current state
of the machine as needed, typically by using a manually-determined
offset into the jmp_buf. (While we might like to get the offset
from the target's jmpbuf.h, that header file cannot be assumed
to be available when building a cross-debugger.)
DEPRECATED_IBM6000_TARGETI386_USE_GENERIC_WATCHPOINTSgdbarch_in_function_epilogue_p (gdbarch, addr)int gdbarch_in_solib_return_trampoline (gdbarch, pc, name)target_so_ops.in_dynsym_resolve_code (pc)SKIP_SOLIB_RESOLVER (pc)CORE_ADDR gdbarch_integer_to_address (gdbarch, type, buf)Pragmatics: When the user copies a well defined expression from
their source code and passes it, as a parameter, to gdb's
print command, they should get the same value as would have been
computed by the target program. Any deviation from this rule can cause
major confusion and annoyance, and needs to be justified carefully. In
other words, gdb doesn't really have the freedom to do these
conversions in clever and useful ways. It has, however, been pointed
out that users aren't complaining about how gdb casts integers
to pointers; they are complaining that they can't take an address from a
disassembly listing and give it to x/i. Adding an architecture
method like gdbarch_integer_to_address certainly makes it possible for
gdb to “get it right” in all circumstances.
CORE_ADDR gdbarch_pointer_to_address (gdbarch, type, buf)void gdbarch_register_to_value(gdbarch, frame, regnum, type, fur)REGISTER_CONVERT_TO_VIRTUAL(reg, type, from, to)REGISTER_CONVERT_TO_RAW(type, reg, from, to)const struct regset *regset_from_core_section (struct gdbarch * gdbarch, const char * sect_name, size_t sect_size)SOFTWARE_SINGLE_STEP_P()SOFTWARE_SINGLE_STEP must also be defined.
SOFTWARE_SINGLE_STEP(signal, insert_breakpoints_p)set_gdbarch_sofun_address_maybe_missing (gdbarch, set)Calling set_gdbarch_sofun_address_maybe_missing with a non-zero
argument set indicates that a particular set of hacks of this sort
are in use, affecting N_SO and N_FUN entries in stabs-format
debugging information. N_SO stabs mark the beginning and ending
addresses of compilation units in the text segment. N_FUN stabs
mark the starts and ends of functions.
In this case, gdb assumes two things:
N_FUN stabs have an address of zero. Instead of using those
addresses, you should find the address where the function starts by
taking the function name from the stab, and then looking that up in the
minsyms (the linker/assembler symbol table). In other words, the stab
has the name, and the linker/assembler symbol table is the only place
that carries the address.
N_SO stabs have an address of zero, too. You just look at the
N_FUN stabs that appear before and after the N_SO stab, and
guess the starting and ending addresses of the compilation unit from them.
int gdbarch_stabs_argument_has_addr (gdbarch, type)CORE_ADDR gdbarch_push_dummy_call (gdbarch, function, regcache, bp_addr, nargs, args, sp, struct_return, struct_addr)function is a pointer to a struct value; on architectures that use
function descriptors, this contains the function descriptor value.
Returns the updated top-of-stack pointer.
CORE_ADDR gdbarch_push_dummy_code (gdbarch, sp, funaddr, using_gcc, args, nargs, value_type, real_pc, bp_addr, regcache)Set bp_addr to the address at which the breakpoint instruction should be inserted, real_pc to the resume address when starting the call sequence, and return the updated inner-most stack address.
By default, the stack is grown sufficient to hold a frame-aligned (see frame_align) breakpoint, bp_addr is set to the address reserved for that breakpoint, and real_pc set to funaddr.
This method replaces gdbarch_call_dummy_location (gdbarch).
int gdbarch_sdb_reg_to_regnum (gdbarch, sdb_regnr)enum return_value_convention gdbarch_return_value (struct gdbarch *gdbarch, struct type *valtype, struct regcache *regcache, void *readbuf, const void *writebuf)gdb currently recognizes two function return-value conventions:
RETURN_VALUE_REGISTER_CONVENTION where the return value is found
in registers; and RETURN_VALUE_STRUCT_CONVENTION where the return
value is found in memory and the address of that memory location is
passed in as the function's first parameter.
If the register convention is being used, and writebuf is
non-NULL, also copy the return-value in writebuf into
regcache.
If the register convention is being used, and readbuf is
non-NULL, also copy the return value from regcache into
readbuf (regcache contains a copy of the registers from the
just returned function).
Maintainer note: This method replaces separate predicate, extract, store methods. By having only one method, the logic needed to determine the return-value convention need only be implemented in one place. If gdb were written in an oo language, this method would instead return an object that knew how to perform the register return-value extract and store.
Maintainer note: This method does not take a gcc_p
parameter, and such a parameter should not be added. If an architecture
that requires per-compiler or per-function information be identified,
then the replacement of rettype with struct value
function should be pursued.
Maintainer note: The regcache parameter limits this methods
to the inner most frame. While replacing regcache with a
struct frame_info frame parameter would remove that
limitation there has yet to be a demonstrated need for such a change.
void gdbarch_skip_permanent_breakpoint (gdbarch, regcache)gdbarch_skip_permanent_breakpoint adjusts the
processor's state so that execution will resume just after the breakpoint.
This function does the right thing even when the breakpoint is in the delay slot
of a branch or jump.
CORE_ADDR gdbarch_skip_trampoline_code (gdbarch, frame, pc)int gdbarch_deprecated_fp_regnum (gdbarch)int gdbarch_stab_reg_to_regnum (gdbarch, stab_regnr)SYMBOL_RELOADING_DEFAULTTARGET_CHAR_BITint gdbarch_char_signed (gdbarch)char is normally signed on this architecture; zero if
it should be unsigned.
The ISO C standard requires the compiler to treat char as
equivalent to either signed char or unsigned char; any
character in the standard execution set is supposed to be positive.
Most compilers treat char as signed, but char is unsigned
on the IBM S/390, RS6000, and PowerPC targets.
int gdbarch_double_bit (gdbarch)8 * TARGET_CHAR_BIT.
int gdbarch_float_bit (gdbarch)4 * TARGET_CHAR_BIT.
int gdbarch_int_bit (gdbarch)4 * TARGET_CHAR_BIT.
int gdbarch_long_bit (gdbarch)4 * TARGET_CHAR_BIT.
int gdbarch_long_double_bit (gdbarch)2 * gdbarch_double_bit (gdbarch).
int gdbarch_long_long_bit (gdbarch)2 * gdbarch_long_bit (gdbarch).
int gdbarch_ptr_bit (gdbarch)gdbarch_int_bit (gdbarch).
int gdbarch_short_bit (gdbarch)2 * TARGET_CHAR_BIT.
void gdbarch_virtual_frame_pointer (gdbarch, pc, frame_regnum, frame_offset)(register, offset) pair representing the virtual
frame pointer in use at the code address pc. If virtual frame
pointers are not used, a default definition simply returns
gdbarch_deprecated_fp_regnum (or gdbarch_sp_regnum, if
no frame pointer is defined), with an offset of zero.
TARGET_HAS_HARDWARE_WATCHPOINTSint gdbarch_print_insn (gdbarch, vma, info)opcodes library
(see Opcodes). info is a structure (of
type disassemble_info) defined in the header file
include/dis-asm.h, and used to pass information to the
instruction decoding routine.
frame_id gdbarch_dummy_id (gdbarch, frame)struct frame_id that uniquely identifies an inferior function call's dummy
frame. The value returned must match the dummy frame stack value
previously saved by call_function_by_hand.
void gdbarch_value_to_register (gdbarch, frame, type, buf)Motorola M68K target conditionals.
BPT_VECTOR0xf.
REMOTE_BPT_VECTOR1.
The following files add a target to gdb:
(Target header files such as gdb/config/arch/tm-ttt.h, gdb/config/arch/tm-arch.h, and config/tm-os.h are no longer used.)
A gdb description for a new architecture, arch is created by
defining a global function _initialize_arch_tdep, by
convention in the source file arch-tdep.c. For
example, in the case of the OpenRISC 1000, this function is called
_initialize_or1k_tdep and is found in the file
or1k-tdep.c.
The object file resulting from compiling this source file, which will
contain the implementation of the
_initialize_arch_tdep function is specified in the
gdb configure.tgt file, which includes a large case
statement pattern matching against the --target option of the
configure script.
Note: If the architecture requires multiple source files, the corresponding binaries should be included in configure.tgt. However if there are header files, the dependencies on these will not be picked up from the entries in configure.tgt. The Makefile.in file will need extending to show these dependencies.
A new struct gdbarch, defining the new architecture, is created within
the _initialize_arch_tdep function by calling
gdbarch_register:
void gdbarch_register (enum bfd_architecture architecture,
gdbarch_init_ftype *init_func,
gdbarch_dump_tdep_ftype *tdep_dump_func);
This function has been described fully in an earlier section. See How an Architecture is Represented.
The new struct gdbarch should contain implementations of
the necessary functions (described in the previous sections) to
describe the basic layout of the target machine's processor chip
(registers, stack, etc.). It can be shared among many targets that use
the same processor architecture.
The target architecture definition (see Target Architecture Definition) contains gdb's hard-coded knowledge about an architecture. For some platforms, it is handy to have more flexible knowledge about a specific instance of the architecture—for instance, a processor or development board. Target descriptions provide a mechanism for the user to tell gdb more about what their target supports, or for the target to tell gdb directly.
For details on writing, automatically supplying, and manually selecting target descriptions, see Target Descriptions. This section will cover some related topics about the gdb internals.
Before gdb connects to a new target, or runs a new program on
an existing target, it discards any existing target description and
reverts to a default gdbarch. Then, after connecting, it looks for a
new target description by calling target_find_description.
A description may come from a user specified file (XML), the remote
`qXfer:features:read' packet (also XML), or from any custom
to_read_description routine in the target vector. For instance,
the remote target supports guessing whether a MIPS target is 32-bit or
64-bit based on the size of the `g' packet.
If any target description is found, gdb creates a new gdbarch
incorporating the description by calling gdbarch_update_p. Any
`<architecture>' element is handled first, to determine which
architecture's gdbarch initialization routine is called to create the
new architecture. Then the initialization routine is called, and has
a chance to adjust the constructed architecture based on the contents
of the target description. For instance, it can recognize any
properties set by a to_read_description routine. Also
see Adding Target Described Register Support.
Target descriptions can report additional registers specific to an instance of the target. But it takes a little work in the architecture specific routines to support this.
A target description must either have no registers or a complete set—this avoids complexity in trying to merge standard registers with the target defined registers. It is the architecture's responsibility to validate that a description with registers has everything it needs. To keep architecture code simple, the same mechanism is used to assign fixed internal register numbers to standard registers.
If tdesc_has_registers returns 1, the description contains
registers. The architecture's gdbarch_init routine should:
tdesc_data_alloc to allocate storage, early, before
searching for a matching gdbarch or allocating a new one.
tdesc_find_feature to locate standard features by name.
tdesc_numbered_register and tdesc_numbered_register_choices
to locate the expected registers in the standard features.
NULL if a required feature is missing, or if any standard
feature is missing expected registers. This will produce a warning that
the description was incomplete.
tdesc_use_registers
is called.
set_gdbarch_num_regs as usual, with a number higher than any
fixed number passed to tdesc_numbered_register.
tdesc_use_registers after creating a new gdbarch, before
returning it.
After tdesc_use_registers has been called, the architecture's
register_name, register_type, and register_reggroup_p
routines will not be called; that information will be taken from
the target description. num_regs may be increased to account
for any additional registers in the description.
Pseudo-registers require some extra care:
tdesc_numbered_register allows the architecture to give
constant register numbers to standard architectural registers, e.g.
as an enum in arch-tdep.h. But because
pseudo-registers are always numbered above num_regs,
which may be increased by the description, constant numbers
can not be used for pseudos. They must be numbered relative to
num_regs instead.
set_tdesc_pseudo_register_name,
set_tdesc_pseudo_register_type, and
set_tdesc_pseudo_register_reggroup_p to supply routines
describing pseudo registers. These routines will be passed
internal register numbers, so the same routines used for the
gdbarch equivalents are usually suitable.
The target vector defines the interface between gdb's abstract handling of target systems, and the nitty-gritty code that actually exercises control over a process or a serial port. gdb includes some 30-40 different target vectors; however, each configuration of gdb includes only a few of them.
A target vector can be completely inactive (not pushed on the target stack), active but not running (pushed, but not connected to a fully manifested inferior), or completely active (pushed, with an accessible inferior). Most targets are only completely inactive or completely active, but some support persistent connections to a target even when the target has exited or not yet started.
For example, connecting to the simulator using target sim does
not create a running program. Neither registers nor memory are
accessible until run. Similarly, after kill, the
program can not continue executing. But in both cases gdb
remains connected to the simulator, and target-specific commands
are directed to the simulator.
A target which only supports complete activation should push itself
onto the stack in its to_open routine (by calling
push_target), and unpush itself from the stack in its
to_mourn_inferior routine (by calling unpush_target).
A target which supports both partial and complete activation should
still call push_target in to_open, but not call
unpush_target in to_mourn_inferior. Instead, it should
call either target_mark_running or target_mark_exited
in its to_open, depending on whether the target is fully active
after connection. It should also call target_mark_running any
time the inferior becomes fully active (e.g. in
to_create_inferior and to_attach), and
target_mark_exited when the inferior becomes inactive (in
to_mourn_inferior). The target should also make sure to call
target_mourn_inferior from its to_kill, to return the
target to inactive state.
Both executables and core files have target vectors.
gdb's file remote.c talks a serial protocol to code that runs in the target system. gdb provides several sample stubs that can be integrated into target programs or operating systems for this purpose; they are named cpu-stub.c. Many operating systems, embedded targets, emulators, and simulators already have a gdb stub built into them, and maintenance of the remote protocol must be careful to preserve compatibility.
The gdb user's manual describes how to put such a stub into your target code. What follows is a discussion of integrating the SPARC stub into a complicated operating system (rather than a simple program), by Stu Grossman, the author of this stub.
The trap handling code in the stub assumes the following upon entry to
trap_low:
As long as your trap handler can guarantee those conditions, then there
is no reason why you shouldn't be able to “share” traps with the stub.
The stub has no requirement that it be jumped to directly from the
hardware trap vector. That is why it calls exceptionHandler(),
which is provided by the external environment. For instance, this could
set up the hardware traps to actually execute code which calls the stub
first, and then transfers to its own trap handler.
For the most point, there probably won't be much of an issue with
“sharing” traps, as the traps we use are usually not used by the kernel,
and often indicate unrecoverable error conditions. Anyway, this is all
controlled by a table, and is trivial to modify. The most important
trap for us is for ta 1. Without that, we can't single step or
do breakpoints. Everything else is unnecessary for the proper operation
of the debugger/stub.
From reading the stub, it's probably not obvious how breakpoints work. They are simply done by deposit/examine operations from gdb.
Several files control gdb's configuration for native support:
Maintainer's note: The .mh suffix is because this file
originally contained Makefile fragments for hosting gdb
on machine xyz. While the file is no longer used for this
purpose, the .mh suffix remains. Perhaps someone will
eventually rename these fragments so that they have a .mn
suffix.
configure). Contains C
macro definitions describing the native system environment, such as
child process control and core file support.
There are some “generic” versions of routines that can be used by
various systems. These can be customized in various ways by macros
defined in your nm-xyz.h file. If these routines work for
the xyz host, you can just include the generic file's name (with
`.o', not `.c') in NATDEPFILES.
Otherwise, if your machine needs custom support routines, you will need
to write routines that perform the same functions as the generic file.
Put them into xyz-nat.c, and put xyz-nat.o
into NATDEPFILES.
ptrace call in a vanilla way.
When gdb is configured and compiled, various macros are defined or left undefined, to control compilation when the host and target systems are the same. These macros should be defined (or left undefined) in nm-system.h.
I386_USE_GENERIC_WATCHPOINTSSOLIB_ADD (filename, from_tty, targ, readsyms)SOLIB_CREATE_INFERIOR_HOOKSTART_INFERIOR_TRAPS_EXPECTEDBFD provides support for gdb in several ways:
The opcodes library provides gdb's disassembler. (It's a separate library because it's also used in binutils, for objdump).
The readline library provides a set of functions for use by applications
that allow users to edit command lines as they are typed in.
The libiberty library provides a set of functions and features
that integrate and improve on functionality found in modern operating
systems. Broadly speaking, such features can be divided into three
groups: supplemental functions (functions that may be missing in some
environments and operating systems), replacement functions (providing
a uniform and easier to use interface for commonly used standard
functions), and extensions (which provide additional functionality
beyond standard functions).
gdb uses various features provided by the libiberty
library, for instance the C++ demangler, the IEEE
floating format support functions, the input options parser
`getopt', the `obstack' extension, and other functions.
obstacks in gdb
The obstack mechanism provides a convenient way to allocate and free
chunks of memory. Each obstack is a pool of memory that is managed
like a stack. Objects (of any nature, size and alignment) are
allocated and freed in a LIFO fashion on an obstack (see
libiberty's documentation for a more detailed explanation of
obstacks).
The most noticeable use of the obstacks in gdb is in
object files. There is an obstack associated with each internal
representation of an object file. Lots of things get allocated on
these obstacks: dictionary entries, blocks, blockvectors,
symbols, minimal symbols, types, vectors of fundamental types, class
fields of types, object files section lists, object files section
offset lists, line tables, symbol tables, partial symbol tables,
string tables, symbol table private data, macros tables, debug
information sections and entries, import and export lists (som),
unwind information (hppa), dwarf2 location expressions data. Plus
various strings such as directory names strings, debug format strings,
names of types.
An essential and convenient property of all data on obstacks is
that memory for it gets allocated (with obstack_alloc) at
various times during a debugging session, but it is released all at
once using the obstack_free function. The obstack_free
function takes a pointer to where in the stack it must start the
deletion from (much like the cleanup chains have a pointer to where to
start the cleanups). Because of the stack like structure of the
obstacks, this allows to free only a top portion of the
obstack. There are a few instances in gdb where such thing
happens. Calls to obstack_free are done after some local data
is allocated to the obstack. Only the local data is deleted from the
obstack. Of course this assumes that nothing between the
obstack_alloc and the obstack_free allocates anything
else on the same obstack. For this reason it is best and safest to
use temporary obstacks.
Releasing the whole obstack is also not safe per se. It is safe only
under the condition that we know the obstacks memory is no
longer needed. In gdb we get rid of the obstacks only
when we get rid of the whole objfile(s), for instance upon reading a
new symbol file.
C_ALLOCA
NFAILURES
RE_NREGS
SIGN_EXTEND_CHAR
SWITCH_ENUM_BUG
SYNTAX_TABLE
Sword
sparcOften it is necessary to manipulate a dynamic array of a set of objects. C forces some bookkeeping on this, which can get cumbersome and repetitive. The vec.h file contains macros for defining and using a typesafe vector type. The functions defined will be inlined when compiling, and so the abstraction cost should be zero. Domain checks are added to detect programming errors.
An example use would be an array of symbols or section information. The array can be grown as symbols are read in (or preallocated), and the accessor macros provided keep care of all the necessary bookkeeping. Because the arrays are type safe, there is no danger of accidentally mixing up the contents. Think of these as C++ templates, but implemented in C.
Because of the different behavior of structure objects, scalar objects
and of pointers, there are three flavors of vector, one for each of
these variants. Both the structure object and pointer variants pass
pointers to objects around — in the former case the pointers are
stored into the vector and in the latter case the pointers are
dereferenced and the objects copied into the vector. The scalar
object variant is suitable for int-like objects, and the vector
elements are returned by value.
There are both index and iterate accessors. The iterator
returns a boolean iteration condition and updates the iteration
variable passed by reference. Because the iterator will be inlined,
the address-of can be optimized away.
The vectors are implemented using the trailing array idiom, thus they
are not resizeable without changing the address of the vector object
itself. This means you cannot have variables or fields of vector type
— always use a pointer to a vector. The one exception is the final
field of a structure, which could be a vector type. You will have to
use the embedded_size & embedded_init calls to create
such objects, and they will probably not be resizeable (so don't use
the safe allocation variants). The trailing array idiom is used
(rather than a pointer to an array of data), because, if we allow
NULL to also represent an empty vector, empty vectors occupy
minimal space in the structure containing them.
Each operation that increases the number of active elements is available in quick and safe variants. The former presumes that there is sufficient allocated space for the operation to succeed (it dies if there is not). The latter will reallocate the vector, if needed. Reallocation causes an exponential increase in vector size. If you know you will be adding N elements, it would be more efficient to use the reserve operation before adding the elements with the quick operation. This will ensure there are at least as many elements as you ask for, it will exponentially increase if there are too few spare slots. If you want reserve a specific number of slots, but do not want the exponential increase (for instance, you know this is the last allocation), use a negative number for reservation. You can also create a vector of a specific size from the get go.
You should prefer the push and pop operations, as they append and
remove from the end of the vector. If you need to remove several items
in one go, use the truncate operation. The insert and remove
operations allow you to change elements in the middle of the vector.
There are two remove operations, one which preserves the element
ordering ordered_remove, and one which does not
unordered_remove. The latter function copies the end element
into the removed slot, rather than invoke a memmove operation. The
lower_bound function will determine where to place an item in
the array using insert that will maintain sorted order.
If you need to directly manipulate a vector, then the address
accessor will return the address of the start of the vector. Also the
space predicate will tell you whether there is spare capacity in the
vector. You will not normally need to use these two functions.
Vector types are defined using a
DEF_VEC_{O,P,I}(typename) macro. Variables of vector
type are declared using a VEC(typename) macro. The
characters O, P and I indicate whether
typename is an object (O), pointer (P) or integral
(I) type. Be careful to pick the correct one, as you'll get an
awkward and inefficient API if you use the wrong one. There is a
check, which results in a compile-time warning, for the P and
I versions, but there is no check for the O versions, as
that is not possible in plain C.
An example of their use would be,
DEF_VEC_P(tree); // non-managed tree vector.
struct my_struct {
VEC(tree) *v; // A (pointer to) a vector of tree pointers.
};
struct my_struct *s;
if (VEC_length(tree, s->v)) { we have some contents }
VEC_safe_push(tree, s->v, decl); // append some decl onto the end
for (ix = 0; VEC_iterate(tree, s->v, ix, elt); ix++)
{ do something with elt }
The vec.h file provides details on how to invoke the various accessors provided. They are enumerated here:
VEC_lengthVEC_emptyVEC_lastVEC_indexVEC_iterateVEC_allocVEC_freeVEC_embedded_sizeVEC_embedded_initVEC_copyVEC_spaceVEC_reserveVEC_quick_pushVEC_safe_pushVEC_popVEC_truncateVEC_safe_growVEC_replaceVEC_quick_insertVEC_safe_insertVEC_ordered_removeVEC_unordered_removeVEC_block_removeVEC_addressVEC_lower_boundgdb follows the GNU coding standards, as described in etc/standards.texi. This file is also available for anonymous FTP from GNU archive sites. gdb takes a strict interpretation of the standard; in general, when the GNU standard recommends a practice but does not require it, gdb requires it.
gdb follows an additional set of coding standards specific to gdb, as described in the following sections.
gdb assumes an ISO/IEC 9899:1990 (a.k.a. ISO C90) compliant compiler.
gdb does not assume an ISO C or POSIX compliant C library.
The standard GNU recommendations for formatting must be followed strictly. Any gdb-specific deviation from GNU recomendations is described below.
A function declaration should not have its name in column zero. A function definition should have its name in column zero.
/* Declaration */
static void foo (void);
/* Definition */
void
foo (void)
{
}
Pragmatics: This simplifies scripting. Function definitions can be found using `^function-name'.
There must be a space between a function or macro name and the opening parenthesis of its argument list (except for macro definitions, as required by C). There must not be a space after an open paren/bracket or before a close paren/bracket.
While additional whitespace is generally helpful for reading, do not use
more than one blank line to separate blocks, and avoid adding whitespace
after the end of a program line (as of 1/99, some 600 lines had
whitespace after the semicolon). Excess whitespace causes difficulties
for diff and patch utilities.
Pointers are declared using the traditional K&R C style:
void *foo;
and not:
void * foo;
void* foo;
In addition, whitespace around casts and unary operators should follow the following guidelines:
| Use... | ...instead of |
|
!x
| ! x
| |
~x
| ~ x
| |
-x
| - x
| (unary minus)
|
(foo) x
| (foo)x
| (cast)
|
*x
| * x
| (pointer dereference)
|
The standard GNU requirements on comments must be followed strictly.
Block comments must appear in the following form, with no /*- or
*/-only lines, and no leading *:
/* Wait for control to return from inferior to debugger. If inferior
gets a signal, we may decide to start it up again instead of
returning. That is why there is a loop in this function. When
this function actually returns it means the inferior should be left
stopped and gdb should read more commands. */
(Note that this format is encouraged by Emacs; tabbing for a multi-line comment works correctly, and M-q fills the block consistently.)
Put a blank line between the block comments preceding function or variable definitions, and the definition itself.
In general, put function-body comments on lines by themselves, rather than trying to fit them into the 20 characters left at the end of a line, since either the comment or the code will inevitably get longer than will fit, and then somebody will have to move it anyhow.
Code must not depend on the sizes of C data types, the format of the host's floating point numbers, the alignment of anything, or the order of evaluation of expressions.
Use functions freely. There are only a handful of compute-bound areas in gdb that might be affected by the overhead of a function call, mainly in symbol reading. Most of gdb's performance is limited by the target interface (whether serial line or system call).
However, use functions with moderation. A thousand one-line functions are just as hard to understand as a single thousand-line function.
Macros are bad, M'kay. (But if you have to use a macro, make sure that the macro arguments are protected with parentheses.)
Declarations like `struct foo *' should be used in preference to declarations like `typedef struct foo { ... } *foo_ptr'.
Prototypes must be used when both declaring and defining a function. Prototypes for gdb functions must include both the argument type and name, with the name matching that used in the actual function definition.
All external functions should have a declaration in a header file that
callers include, except for _initialize_* functions, which must
be external so that init.c construction works, but shouldn't be
visible to random source files.
Where a source file needs a forward declaration of a static function, that declaration must appear in a block near the top of the source file.
Any file used when building the core of gdb must be in lower case. Any file used when building the core of gdb must be 8.3 unique. These requirements apply to both source and generated files.
Pragmatics: The core of gdb must be buildable on many platforms including DJGPP and MacOS/HFS. Every time an unfriendly file is introduced to the build process both Makefile.in and configure.in need to be modified accordingly. Compare the convoluted conversion process needed to transform COPYING into copying.c with the conversion needed to transform version.in into version.c.
Any file non 8.3 compliant file (that is not used when building the core of gdb) must be added to gdb/config/djgpp/fnchange.lst.
Pragmatics: This is clearly a compromise.
When gdb has a local version of a system header file (ex string.h) the file name based on the POSIX header prefixed with gdb_ (gdb_string.h). These headers should be relatively independent: they should use only macros defined by configure, the compiler, or the host; they should include only system headers; they should refer only to system types. They may be shared between multiple programs, e.g. gdb and gdbserver.
For other files `-' is used as the separator.
A .c file should include defs.h first.
A .c file should directly include the .h file of every
declaration and/or definition it directly refers to. It cannot rely on
indirect inclusion.
A .h file should directly include the .h file of every
declaration and/or definition it directly refers to. It cannot rely on
indirect inclusion. Exception: The file defs.h does not need to
be directly included.
An external declaration should only appear in one include file.
An external declaration should never appear in a .c file.
Exception: a declaration for the _initialize function that
pacifies -Wmissing-declaration.
A typedef definition should only appear in one include file.
An opaque struct declaration can appear in multiple .h
files. Where possible, a .h file should use an opaque
struct declaration instead of an include.
All .h files should be wrapped in:
#ifndef INCLUDE_FILE_NAME_H
#define INCLUDE_FILE_NAME_H
header body
#endif
gdb follows the published Python coding standards in
PEP008.
In addition, the guidelines in the
Google Python Style Guide are also followed where they do not
conflict with PEP008.
There are a few exceptions to the published standards.
They exist mainly for consistency with the C standards.
FIXME instead of TODO.
This chapter covers topics that are lower-level than the major algorithms of gdb.
Cleanups are a structured way to deal with things that need to be done later.
When your code does something (e.g., xmalloc some memory, or
open a file) that needs to be undone later (e.g., xfree
the memory or close the file), it can make a cleanup. The
cleanup will be done at some future point: when the command is finished
and control returns to the top level; when an error occurs and the stack
is unwound; or when your code decides it's time to explicitly perform
cleanups. Alternatively you can elect to discard the cleanups you
created.
Syntax:
struct cleanup *old_chain; = make_cleanup (function, arg);char *) later. The result, old_chain, is a
handle that can later be passed to do_cleanups or
discard_cleanups. Unless you are going to call
do_cleanups or discard_cleanups, you can ignore the result
from make_cleanup.
do_cleanups (old_chain);make_cleanup call was made.
discard_cleanups (old_chain);do_cleanups except that it just removes the cleanups from
the chain and does not call the specified functions.
Cleanups are implemented as a chain. The handle returned by
make_cleanups includes the cleanup passed to the call and any
later cleanups appended to the chain (but not yet discarded or
performed). E.g.:
make_cleanup (a, 0);
{
struct cleanup *old = make_cleanup (b, 0);
make_cleanup (c, 0)
...
do_cleanups (old);
}
will call c() and b() but will not call a(). The
cleanup that calls a() will remain in the cleanup chain, and will
be done later unless otherwise discarded.
Your function should explicitly do or discard the cleanups it creates. Failing to do this leads to non-deterministic behavior since the caller will arbitrarily do or discard your functions cleanups. This need leads to two common cleanup styles.
The first style is try/finally. Before it exits, your code-block calls
do_cleanups with the old cleanup chain and thus ensures that your
code-block's cleanups are always performed. For instance, the following
code-segment avoids a memory leak problem (even when error is
called and a forced stack unwind occurs) by ensuring that the
xfree will always be called:
struct cleanup *old = make_cleanup (null_cleanup, 0);
data = xmalloc (sizeof blah);
make_cleanup (xfree, data);
... blah blah ...
do_cleanups (old);
The second style is try/except. Before it exits, your code-block calls
discard_cleanups with the old cleanup chain and thus ensures that
any created cleanups are not performed. For instance, the following
code segment, ensures that the file will be closed but only if there is
an error:
FILE *file = fopen ("afile", "r");
struct cleanup *old = make_cleanup (close_file, file);
... blah blah ...
discard_cleanups (old);
return file;
Some functions, e.g., fputs_filtered() or error(), specify
that they “should not be called when cleanups are not in place”. This
means that any actions you need to reverse in the case of an error or
interruption must be on the cleanup chain before you call these
functions, since they might never return to your code (they
`longjmp' instead).
The multi-arch framework includes a mechanism for adding module
specific per-architecture data-pointers to the struct gdbarch
architecture object.
A module registers one or more per-architecture data-pointers using:
pre_init is used to, on-demand, allocate an initial value for a per-architecture data-pointer using the architecture's obstack (passed in as a parameter). Since pre_init can be called during architecture creation, it is not parameterized with the architecture. and must not call modules that use per-architecture data.
post_init is used to obtain an initial value for a per-architecture data-pointer after. Since post_init is always called after architecture creation, it both receives the fully initialized architecture and is free to call modules that use per-architecture data (care needs to be taken to ensure that those other modules do not try to call back to this module as that will create in cycles in the initialization call graph).
These functions return a struct gdbarch_data that is used to
identify the per-architecture data-pointer added for that module.
The per-architecture data-pointer is accessed using the function:
Given the architecture arch and module data handle data_handle (returned by
gdbarch_data_register_pre_initorgdbarch_data_register_post_init), this function returns the current value of the per-architecture data-pointer. If the data pointer isNULL, it is first initialized by calling the corresponding pre_init or post_init method.
The examples below assume the following definitions:
struct nozel { int total; };
static struct gdbarch_data *nozel_handle;
A module can extend the architecture vector, adding additional per-architecture data, using the pre_init method. The module's per-architecture data is then initialized during architecture creation.
In the below, the module's per-architecture nozel is added. An
architecture can specify its nozel by calling set_gdbarch_nozel
from gdbarch_init.
static void *
nozel_pre_init (struct obstack *obstack)
{
struct nozel *data = OBSTACK_ZALLOC (obstack, struct nozel);
return data;
}
extern void
set_gdbarch_nozel (struct gdbarch *gdbarch, int total)
{
struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
data->total = nozel;
}
A module can on-demand create architecture dependent data structures
using post_init.
In the below, the nozel's total is computed on-demand by
nozel_post_init using information obtained from the
architecture.
static void *
nozel_post_init (struct gdbarch *gdbarch)
{
struct nozel *data = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct nozel);
nozel->total = gdbarch... (gdbarch);
return data;
}
extern int
nozel_total (struct gdbarch *gdbarch)
{
struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
return data->total;
}
Output that goes through printf_filtered or fputs_filtered
or fputs_demangled needs only to have calls to wrap_here
added in places that would be good breaking points. The utility
routines will take care of actually wrapping if the line width is
exceeded.
The argument to wrap_here is an indentation string which is
printed only if the line breaks there. This argument is saved
away and used later. It must remain valid until the next call to
wrap_here or until a newline has been printed through the
*_filtered functions. Don't pass in a local variable and then
return!
It is usually best to call wrap_here after printing a comma or
space. If you call it before printing a space, make sure that your
indentation properly accounts for the leading space that will print if
the line wraps there.
Any function or set of functions that produce filtered output must
finish by printing a newline, to flush the wrap buffer, before switching
to unfiltered (printf) output. Symbol reading routines that
print warnings are a good example.
gdb does not use the functions malloc, realloc,
calloc, free and asprintf.
gdb uses the functions xmalloc, xrealloc and
xcalloc when allocating memory. Unlike malloc et.al.
these functions do not return when the memory pool is empty. Instead,
they unwind the stack using cleanups. These functions return
NULL when requested to allocate a chunk of memory of size zero.
Pragmatics: By using these functions, the need to check every memory allocation is removed. These functions provide portable behavior.
gdb does not use the function free.
gdb uses the function xfree to return memory to the
memory pool. Consistent with ISO-C, this function ignores a request to
free a NULL pointer.
Pragmatics: On some systems free fails when passed a
NULL pointer.
gdb can use the non-portable function alloca for the
allocation of small temporary values (such as strings).
Pragmatics: This function is very non-portable. Some systems restrict the memory being allocated to no more than a few kilobytes.
gdb uses the string function xstrdup and the print
function xstrprintf.
Pragmatics: asprintf and strdup can fail. Print
functions such as sprintf are very prone to buffer overflow
errors.
With few exceptions, developers should avoid the configuration option `--disable-werror' when building gdb. The exceptions are listed in the file gdb/MAINTAINERS. The default, when building with gcc, is `--enable-werror'.
This option causes gdb (when built using GCC) to be compiled with a carefully selected list of compiler warning flags. Any warnings from those flags are treated as errors.
The current list of warning flags includes:
format printf attribute on all
printf like functions this checks not just printf calls
but also calls to functions such as fprintf_unfiltered.
char and unsigned char. In early 2006
the gdb developers decided correcting these warnings wasn't
worth the time it would take.
ATTRIBUTE_UNUSED is not used as it leads to false negatives —
it is not an error to have ATTRIBUTE_UNUSED on a parameter that
is being used.
During its execution, gdb can encounter two types of errors. User errors and internal errors. User errors include not only a user entering an incorrect command but also problems arising from corrupt object files and system errors when interacting with the target. Internal errors include situations where gdb has detected, at run time, a corrupt or erroneous situation.
When reporting an internal error, gdb uses
internal_error and gdb_assert.
gdb must not call abort or assert.
Pragmatics: There is no internal_warning function. Either
the code detected a user error, recovered from it and issued a
warning or the code failed to correctly recover from the user
error and issued an internal_error.
GDB U/I commands are written `foo-bar', not `foo_bar'.
In addition to getting the syntax right, there's the little question of semantics. Some things are done in certain ways in gdb because long experience has shown that the more obvious ways caused various kinds of trouble.
You can't assume the byte order of anything that comes from a target
(including values, object files, and instructions). Such things
must be byte-swapped using SWAP_TARGET_AND_HOST in
gdb, or one of the swap routines defined in bfd.h,
such as bfd_get_32.
You can't assume that you know what interface is being used to talk to
the target system. All references to the target must go through the
current target_ops vector.
You can't assume that the host and target machines are the same machine (except in the “native” support modules). In particular, you can't assume that the target machine's header files will be available on the host machine. Target code must bring along its own header files – written from scratch or explicitly donated by their owner, to avoid copyright problems.
Insertion of new #ifdef's will be frowned upon. It's much better
to write the code portably than to conditionalize it for various
systems.
New #ifdef's which test for specific compilers or manufacturers
or operating systems are unacceptable. All #ifdef's should test
for features. The information about which configurations contain which
features should be segregated into the configuration files. Experience
has proven far too often that a feature unique to one particular system
often creeps into other systems; and that a conditional based on some
predefined macro for your current system will become worthless over
time, as new versions of your system come out that behave differently
with regard to this feature.
Adding code that handles specific architectures, operating systems, target interfaces, or hosts, is not acceptable in generic code.
One particularly notorious area where system dependencies tend to creep in is handling of file names. The mainline gdb code assumes Posix semantics of file names: absolute file names begin with a forward slash /, slashes are used to separate leading directories, case-sensitive file names. These assumptions are not necessarily true on non-Posix systems such as MS-Windows. To avoid system-dependent code where you need to take apart or construct a file name, use the following portable macros:
HAVE_DOS_BASED_FILE_SYSTEMIS_DIR_SEPARATOR (c)IS_ABSOLUTE_PATH (file)FILENAME_CMP (f1, f2)strcmp; on case-insensitive filesystems it
will call strcasecmp instead.
DIRNAME_SEPARATORPATH-style lists, typically held in environment variables.
This character is `:' on Unix, `;' on DOS and Windows.
SLASH_STRINGSLASH_STRING is "/" on most systems, but might be
"\\" for some Windows-based ports.
In addition to using these macros, be sure to use portable library
functions whenever possible. For example, to extract a directory or a
basename part from a file name, use the dirname and
basename library functions (available in libiberty for
platforms which don't provide them), instead of searching for a slash
with strrchr.
Another way to generalize gdb along a particular interface is with an
attribute struct. For example, gdb has been generalized to handle
multiple kinds of remote interfaces—not by #ifdefs everywhere, but
by defining the target_ops structure and having a current target (as
well as a stack of targets below it, for memory references). Whenever
something needs to be done that depends on which remote interface we are
using, a flag in the current target_ops structure is tested (e.g.,
target_has_stack), or a function is called through a pointer in the
current target_ops structure. In this way, when a new remote interface
is added, only one module needs to be touched—the one that actually
implements the new remote interface. Other examples of
attribute-structs are BFD access to multiple kinds of object file
formats, or gdb's access to multiple source languages.
Please avoid duplicating code. For example, in gdb 3.x all
the code interfacing between ptrace and the rest of
gdb was duplicated in *-dep.c, and so changing
something was very painful. In gdb 4.x, these have all been
consolidated into infptrace.c. infptrace.c can deal
with variations between systems the same way any system-independent
file would (hooks, #if defined, etc.), and machines which are
radically different don't need to use infptrace.c at all.
All debugging code must be controllable using the `set debug
module' command. Do not use printf to print trace
messages. Use fprintf_unfiltered(gdb_stdlog, .... Do not use
#ifdef DEBUG.
Most of the work in making gdb compile on a new machine is in specifying the configuration of the machine. Porting a new architecture to gdb can be broken into a number of steps.
Within arch-tdep.c define the function
_initialize_arch_tdep which calls
gdbarch_register to create the new struct gdbarch for the architecture.
_initialize_remote_arch. However if at all possible
use the gdb Remote Serial Protocol for this and implement
the server side protocol independently with the target.
gdb's version is determined by the file gdb/version.in and takes one of the following forms:
gdb's mainline uses the major and minor version numbers from the most recent release branch, with a patchlevel of 50. At the time each new release branch is created, the mainline's major and minor version numbers are updated.
gdb's release branch is similar. When the branch is cut, the patchlevel is changed from 50 to 90. As draft releases are drawn from the branch, the patchlevel is incremented. Once the first release (major.minor) has been made, the patchlevel is set to 0 and updates have an incremented patchlevel.
For snapshots, and cvs check outs, it is also possible to identify the cvs origin:
If the previous gdb version is 6.1 and the current version is 6.2, then, substituting 6 for major and 1 or 2 for minor, here's an illustration of a typical sequence:
<HEAD>
|
6.1.50.20020302-cvs
|
+--------------------------.
| <gdb_6_2-branch>
| |
6.2.50.20020303-cvs 6.1.90 (draft #1)
| |
6.2.50.20020304-cvs 6.1.90.20020304-cvs
| |
6.2.50.20020305-cvs 6.1.91 (draft #2)
| |
6.2.50.20020306-cvs 6.1.91.20020306-cvs
| |
6.2.50.20020307-cvs 6.2 (release)
| |
6.2.50.20020308-cvs 6.2.0.20020308-cvs
| |
6.2.50.20020309-cvs 6.2.1 (update)
| |
6.2.50.20020310-cvs <branch closed>
|
6.2.50.20020311-cvs
|
+--------------------------.
| <gdb_6_3-branch>
| |
6.3.50.20020312-cvs 6.2.90 (draft #1)
| |
gdb draws a release series (6.2, 6.2.1, ...) from a single release branch, and identifies that branch using the cvs branch tags:
gdb_major_minor-YYYYMMDD-branchpoint
gdb_major_minor-branch
gdb_major_minor-YYYYMMDD-release
Pragmatics: To help identify the date at which a branch or release is made, both the branchpoint and release tags include the date that they are cut (YYYYMMDD) in the tag. The branch tag, denoting the head of the branch, does not need this.
To avoid version conflicts, vendors are expected to modify the file gdb/version.in to include a vendor unique alphabetic identifier (an official gdb release never uses alphabetic characters in its version identifier). E.g., `6.2widgit2', or `6.2 (Widgit Inc Patch 2)'.
gdb permits the creation of branches, cut from the cvs repository, for experimental development. Branches make it possible for developers to share preliminary work, and maintainers to examine significant new developments.
The following are a set of guidelines for creating such branches:
gdb should be specified when creating a
branch (branches of individual files should be avoided). See Tags.
To simplify the identification of gdb branches, the following branch tagging convention is strongly recommended:
_name-YYYYMMDD-branchpoint_name-YYYYMMDD-branch cvs rtag owner_name-YYYYMMDD-branchpoint gdb
cvs rtag -b -r owner_name-YYYYMMDD-branchpoint \
owner_name-YYYYMMDD-branch gdb
_name-yyyymmdd-mergepoint cvs rtag owner_name-yyyymmdd-mergepoint gdb
cvs update \
-jowner_name-YYYYMMDD-branchpoint
-jowner_name-yyyymmdd-mergepoint
Similar sequences can be used to just merge in changes since the last merge.
For further information on cvs, see Concurrent Versions System.
At the start of each new year, the following actions should be performed:
The current ChangeLog file should be renamed into ChangeLog-YYYY where YYYY is the year that has just passed. A new ChangeLog file should be created, and its contents should contain a reference to the previous ChangeLog. The following should also be preserved at the end of the new ChangeLog, in order to provide the appropriate settings when editing this file with Emacs:
Local Variables:
mode: change-log
left-margin: 8
fill-column: 74
version-control: never
coding: utf-8
End:
Update the copyright year in:
print_gdb_version
gdbserver_version
gdbreplay_version
The branch commit policy is pretty slack. gdb releases 5.0, 5.1 and 5.2 all used the below:
Pragmatics: Provided updates are restricted to non-core functionality there is little chance that a broken change will be fatal. This means that changes such as adding a new architectures or (within reason) support for a new host are considered acceptable.
Before anything else, poke the other developers (and around the source code) to see if there is anything that can be removed from gdb (an old target, an unused file).
Obsolete code is identified by adding an OBSOLETE prefix to every
line. Doing this means that it is easy to identify something that has
been obsoleted when greping through the sources.
The process is done in stages — this is mainly to ensure that the wider gdb community has a reasonable opportunity to respond. Remember, everything on the Internet takes a week.
OBSOLETE.
Maintainer note: While removing old code is regrettable it is hopefully better for gdb's long term development. Firstly it helps the developers by removing code that is either no longer relevant or simply wrong. Secondly since it removes any history associated with the file (effectively clearing the slate) the developer has a much freer hand when it comes to fixing broken files.
The most important objective at this stage is to find and fix simple changes that become a pain to track once the branch is created. For instance, configuration problems that stop gdb from even building. If you can't get the problem fixed, document it in the gdb/PROBLEMS file.
People always forget. Send a post reminding them but also if you know
something interesting happened add it yourself. The schedule
script will mention this in its e-mail.
Grab one of the nightly snapshots and then walk through the
gdb/README looking for anything that can be improved. The
schedule script will mention this in its e-mail.
A number of files are taken from external repositories. They include:
A.R.I. is an awk script
(Awk Regression Index ;-) that checks for a number of errors and coding
conventions. The checks include things like using malloc instead
of xmalloc and file naming problems. There shouldn't be any
regressions.
Close anything obviously fixed.
The targets are listed in gdb/MAINTAINERS.
$ u=5.1
$ v=5.2
$ V=`echo $v | sed 's/\./_/g'`
$ D=`date -u +%Y-%m-%d`
$ echo $u $V $D
5.1 5_2 2002-03-03
$ echo cvs -f -d :ext:sourceware.org:/cvs/src rtag \
-D $D-gmt gdb_$V-$D-branchpoint insight
cvs -f -d :ext:sourceware.org:/cvs/src rtag
-D 2002-03-03-gmt gdb_5_2-2002-03-03-branchpoint insight
$ ^echo ^^
...
$ echo cvs -f -d :ext:sourceware.org:/cvs/src rtag \
-b -r gdb_$V-$D-branchpoint gdb_$V-branch insight
cvs -f -d :ext:sourceware.org:/cvs/src rtag \
-b -r gdb_5_2-2002-03-03-branchpoint gdb_5_2-branch insight
$ ^echo ^^
...
$
$ u=5.1
$ v=5.2
$ V=`echo $v | sed 's/\./_/g'`
$ echo $u $v$V
5.1 5_2
$ cd /tmp
$ echo cvs -f -d :ext:sourceware.org:/cvs/src co \
-r gdb_$V-branch src/gdb/version.in
cvs -f -d :ext:sourceware.org:/cvs/src co
-r gdb_5_2-branch src/gdb/version.in
$ ^echo ^^
U src/gdb/version.in
$ cd src/gdb
$ echo $u.90-0000-00-00-cvs > version.in
$ cat version.in
5.1.90-0000-00-00-cvs
$ cvs -f commit version.in
Something?
The file gdbadmin/cron/crontab contains gdbadmin's cron table. This file needs to be updated so that:
See the file gdbadmin/cron/README for how to install the updated cron table.
The file gdbadmin/ss/README should also be reviewed to reflect any changes. That file is copied to both the branch/ and current/ snapshot directories.
The NEWS file needs to be updated so that on the branch it refers to changes in the current release while on the trunk it also refers to changes since the current release.
The README file needs to be updated so that it refers to the current release.
Send an announcement to the mailing lists:
Pragmatics: The branch creation is sent to the announce list to ensure that people people not subscribed to the higher volume discussion list are alerted.
The announcement should include:
Something goes here.
The process of creating and then making available a release is broken down into a number of stages. The first part addresses the technical process of creating a releasable tar ball. The later stages address the process of releasing that tar ball.
When making a release candidate just the first section is needed.
The objective at this stage is to create a set of tar balls that can be made available as a formal release (or as a less formal release candidate).
Send out an e-mail notifying everyone that the branch is frozen to gdb-patches@sourceware.org.
$ b=gdb_5_2-branch
$ v=5.2
$ t=/sourceware/snapshot-tmp/gdbadmin-tmp
$ echo $t/$b/$v
/sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
$ mkdir -p $t/$b/$v
$ cd $t/$b/$v
$ pwd
/sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
$ which autoconf
/home/gdbadmin/bin/autoconf
$
Notes:
autoconf version carefully. You want to be using the
version documented in the toplevel README-maintainer-mode file.
It is very unlikely that the version of autoconf installed in
system directories (e.g., /usr/bin/autoconf) is correct.
$ for m in gdb insight
do
( mkdir -p $m && cd $m && cvs -q -f -d /cvs/src co -P -r $b $m )
done
$
Note:
cvs really does.
Don't forget to include the ChangeLog entry.
$ emacs gdb/src/gdb/NEWS
...
c-x 4 a
...
c-x c-s c-x c-c
$ cp gdb/src/gdb/NEWS insight/src/gdb/NEWS
$ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
$ emacs gdb/src/gdb/README
...
c-x 4 a
...
c-x c-s c-x c-c
$ cp gdb/src/gdb/README insight/src/gdb/README
$ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
Maintainer note: Hopefully the README file was reviewed before the initial branch was cut so just a simple substitute is needed to get it updated.
Maintainer note: Other projects generate README and
INSTALL from the core documentation. This might be worth
pursuing.
$ echo $v > gdb/src/gdb/version.in
$ cat gdb/src/gdb/version.in
5.2
$ emacs gdb/src/gdb/version.in
...
c-x 4 a
... Bump to version ...
c-x c-s c-x c-c
$ cp gdb/src/gdb/version.in insight/src/gdb/version.in
$ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
This is identical to the process used to create the daily snapshot.
$ for m in gdb insight
do
( cd $m/src && gmake -f src-release $m.tar )
done
If the top level source directory does not have src-release (gdb version 5.3.1 or earlier), try these commands instead:
$ for m in gdb insight
do
( cd $m/src && gmake -f Makefile.in $m.tar )
done
You're looking for files that have mysteriously disappeared. distclean has the habit of deleting files it shouldn't. Watch out for the version.in update cronjob.
$ ( cd gdb/src && cvs -f -q -n update )
M djunpack.bat
? gdb-5.1.91.tar
? proto-toplev
... lots of generated files ...
M gdb/ChangeLog
M gdb/NEWS
M gdb/README
M gdb/version.in
... lots of generated files ...
$
Don't worry about the gdb.info-?? or gdb/p-exp.tab.c. They were generated (and yes gdb.info-1 was also generated only something strange with CVS means that they didn't get suppressed). Fixing it would be nice though.
$ cp */src/*.tar .
$ cp */src/*.bz2 .
$ ls -F
gdb/ gdb-5.2.tar insight/ insight-5.2.tar
$ for m in gdb insight
do
bzip2 -v -9 -c $m-$v.tar > $m-$v.tar.bz2
gzip -v -9 -c $m-$v.tar > $m-$v.tar.gz
done
$
Note:
gzip does not know the name of the file and, hence,
can not include it in the compressed file. This is also why the release
process runs tar and bzip2 as separate passes.
Pick a popular machine (Solaris/PPC?) and try the build on that.
$ bunzip2 < gdb-5.2.tar.bz2 | tar xpf -
$ cd gdb-5.2
$ ./configure
$ make
...
$ ./gdb/gdb ./gdb/gdb
GNU gdb 5.2
...
(gdb) b main
Breakpoint 1 at 0x80732bc: file main.c, line 734.
(gdb) run
Starting program: /tmp/gdb-5.2/gdb/gdb
Breakpoint 1, main (argc=1, argv=0xbffff8b4) at main.c:734
734 catch_errors (captured_main, &args, "", RETURN_MASK_ALL);
(gdb) print args
$1 = {argc = 136426532, argv = 0x821b7f0}
(gdb)
If this is a release candidate then the only remaining steps are:
(And you thought all that was required was to post an e-mail.)
Copy the new files to both the release and the old release directory:
$ cp *.bz2 *.gz ~ftp/pub/gdb/old-releases/
$ cp *.bz2 *.gz ~ftp/pub/gdb/releases
Clean up the releases directory so that only the most recent releases are available (e.g. keep 5.2 and 5.2.1 but remove 5.1):
$ cd ~ftp/pub/gdb/releases
$ rm ...
Update the file README and .message in the releases directory:
$ vi README
...
$ rm -f .message
$ ln README .message
index.sh.
cron jobs and then just edit accordingly.
Something like:
$ ~/ss/update-web-docs \
~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
$PWD/www \
/www/sourceware/htdocs/gdb/download/onlinedocs \
gdb
$ /bin/sh ~/ss/update-web-ari \
~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
$PWD/www \
/www/sourceware/htdocs/gdb/download/ari \
gdb
Something goes here.
At the time of writing, the GNU machine was gnudist.gnu.org in ~ftp/gnu/gdb.
Post the ANNOUNCEMENT file you created above to:
The release is out but you're still not finished.
In particular you'll need to commit any changes to:
Something like:
$ d=`date -u +%Y-%m-%d`
$ echo $d
2002-01-24
$ ( cd insight/src/gdb && cvs -f -q update )
$ ( cd insight/src && cvs -f -q tag gdb_5_2-$d-release )
Insight is used since that contains more of the release than gdb.
Just put something in the ChangeLog so that the trunk also indicates when the release was made.
If gdb/version.in does not contain an ISO date such as
2002-01-24 then the daily cronjob won't update it. Having
committed all the release changes it can be set to
5.2.0_0000-00-00-cvs which will restart things (yes the _
is important - it affects the snapshot process).
Don't forget the ChangeLog.
The files committed to the branch may also need changes merged into the trunk.
Post a revised release schedule to GDB Discussion List with an updated announcement. The schedule can be generated by running:
$ ~/ss/schedule `date +%s` schedule
The first parameter is approximate date/time in seconds (from the epoch) of the most recent release.
Also update the schedule cronjob.
Remove any OBSOLETE code.
The testsuite is an important component of the gdb package. While it is always worthwhile to encourage user testing, in practice this is rarely sufficient; users typically use only a small subset of the available commands, and it has proven all too common for a change to cause a significant regression that went unnoticed for some time.
The gdb testsuite uses the DejaGNU testing framework. The
tests themselves are calls to various Tcl procs; the framework
runs all the procs and summarizes the passes and fails.
To run the testsuite, simply go to the gdb object directory (or to the
testsuite's objdir) and type make check. This just sets up some
environment variables and invokes DejaGNU's runtest script. While
the testsuite is running, you'll get mentions of which test file is in use,
and a mention of any unexpected passes or fails. When the testsuite is
finished, you'll get a summary that looks like this:
=== gdb Summary ===
# of expected passes 6016
# of unexpected failures 58
# of unexpected successes 5
# of expected failures 183
# of unresolved testcases 3
# of untested testcases 5
To run a specific test script, type:
make check RUNTESTFLAGS='tests'
where tests is a list of test script file names, separated by spaces.
If you use GNU make, you can use its -j option to run the
testsuite in parallel. This can greatly reduce the amount of time it
takes for the testsuite to run. In this case, if you set
RUNTESTFLAGS then, by default, the tests will be run serially
even under -j. You can override this and force a parallel run
by setting the make variable FORCE_PARALLEL to any
non-empty value. Note that the parallel make check assumes
that you want to run the entire testsuite, so it is not compatible
with some dejagnu options, like --directory.
The ideal test run consists of expected passes only; however, reality conspires to keep us from this ideal. Unexpected failures indicate real problems, whether in gdb or in the testsuite. Expected failures are still failures, but ones which have been decided are too hard to deal with at the time; for instance, a test case might work everywhere except on AIX, and there is no prospect of the AIX case being fixed in the near future. Expected failures should not be added lightly, since you may be masking serious bugs in gdb. Unexpected successes are expected fails that are passing for some reason, while unresolved and untested cases often indicate some minor catastrophe, such as the compiler being unable to deal with a test program.
When making any significant change to gdb, you should run the testsuite before and after the change, to confirm that there are no regressions. Note that truly complete testing would require that you run the testsuite with all supported configurations and a variety of compilers; however this is more than really necessary. In many cases testing with a single configuration is sufficient. Other useful options are to test one big-endian (Sparc) and one little-endian (x86) host, a cross config with a builtin simulator (powerpc-eabi, mips-elf), or a 64-bit host (Alpha).
If you add new functionality to gdb, please consider adding tests for it as well; this way future gdb hackers can detect and fix their changes that break the functionality you added. Similarly, if you fix a bug that was not previously reported as a test failure, please add a test case for it. Some cases are extremely difficult to test, such as code that handles host OS failures or bugs in particular versions of compilers, and it's OK not to try to write tests for all of those.
DejaGNU supports separate build, host, and target machines. However, some gdb test scripts do not work if the build machine and the host machine are not the same. In such an environment, these scripts will give a result of “UNRESOLVED”, like this:
UNRESOLVED: gdb.base/example.exp: This test script does not work on a remote host.
Several variables exist to modify the behavior of the testsuite.
TRANSCRIPT
Sometimes it is convenient to get a transcript of the commands which the testsuite sends to gdb. For example, if gdb crashes during testing, a transcript can be used to more easily reconstruct the failure when running gdb under gdb.
You can instruct the gdb testsuite to write transcripts by
setting the DejaGNU variable TRANSCRIPT (to any value)
before invoking runtest or make check. The transcripts
will be written into DejaGNU's output directory. One transcript will
be made for each invocation of gdb; they will be named
transcript.n, where n is an integer. The first
line of the transcript file will show how gdb was invoked;
each subsequent line is a command sent as input to gdb.
make check RUNTESTFLAGS=TRANSCRIPT=y
Note that the transcript is not always complete. In particular, tests of completion can yield partial command lines.
GDB
Sometimes one wishes to test a different gdb than the one in the build directory. For example, one may wish to run the testsuite on /usr/bin/gdb.
make check RUNTESTFLAGS=GDB=/usr/bin/gdb
GDBSERVER
When testing a different gdb, it is often useful to also test a different gdbserver.
make check RUNTESTFLAGS="GDB=/usr/bin/gdb GDBSERVER=/usr/bin/gdbserver"
INTERNAL_GDBFLAGS
When running the testsuite normally one doesn't want whatever is in
~/.gdbinit to interfere with the tests, therefore the test harness
passes -nx to gdb. One also doesn't want any windowed
version of gdb, e.g., gdbtui, to run.
This is achieved via INTERNAL_GDBFLAGS.
set INTERNAL_GDBFLAGS "-nw -nx"
This is all well and good, except when testing an installed gdb
that has been configured with --with-system-gdbinit. Here one
does not want ~/.gdbinit loaded but one may want the system
.gdbinit file loaded. This can be achieved by pointing $HOME
at a directory without a .gdbinit and by overriding
INTERNAL_GDBFLAGS and removing -nx.
cd testsuite
HOME=`pwd` runtest \
GDB=/usr/bin/gdb \
GDBSERVER=/usr/bin/gdbserver \
INTERNAL_GDBFLAGS=-nw
There are two ways to run the testsuite and pass additional parameters to DejaGnu. The first is with make check and specifying the makefile variable `RUNTESTFLAGS'.
make check RUNTESTFLAGS=TRANSCRIPT=y
The second is to cd to the testsuite directory and invoke the DejaGnu runtest command directly.
cd testsuite
make site.exp
runtest TRANSCRIPT=y
It is possible to adjust the behavior of the testsuite by defining the global variables listed below, either in a site.exp file, or in a board file.
gdb_test_timeout
Defining this variable changes the default timeout duration used during
communication with gdb. More specifically, the global variable
used during testing is timeout, but this variable gets reset to
gdb_test_timeout at the beginning of each testcase, making sure
that any local change to timeout in a testcase does not affect
subsequent testcases.
This global variable comes in handy when the debugger is slower than
normal due to the testing environment, triggering unexpected TIMEOUT
test failures. Examples include when testing on a remote machine, or
against a system where communications are slow.
If not specifically defined, this variable gets automatically defined
to the same value as timeout during the testsuite initialization.
The default value of the timeout is defined in the file
gdb/testsuite/config/unix.exp that is part of the gdb
test suite7.
The testsuite is entirely contained in gdb/testsuite. While the
testsuite includes some makefiles and configury, these are very minimal,
and used for little besides cleaning up, since the tests themselves
handle the compilation of the programs that gdb will run. The file
testsuite/lib/gdb.exp contains common utility procs useful for
all gdb tests, while the directory testsuite/config contains
configuration-specific files, typically used for special-purpose
definitions of procs like gdb_load and gdb_start.
The tests themselves are to be found in testsuite/gdb.* and subdirectories of those. The names of the test files must always end with .exp. DejaGNU collects the test files by wildcarding in the test directories, so both subdirectories and individual files get chosen and run in alphabetical order.
The following table lists the main types of subdirectories and what they are for. Since DejaGNU finds test files no matter where they are located, and since each test file sets up its own compilation and execution environment, this organization is simply for convenience and intelligibility.
#ifdefs are allowed if necessary, for instance
for prototypes).
In many areas, the gdb tests are already quite comprehensive; you should be able to copy existing tests to handle new cases.
You should try to use gdb_test whenever possible, since it
includes cases to handle all the unexpected errors that might happen.
However, it doesn't cost anything to add new test procedures; for
instance, gdb.base/exprs.exp defines a test_expr that
calls gdb_test multiple times.
Only use send_gdb and gdb_expect when absolutely
necessary. Even if gdb has several valid responses to
a command, you can use gdb_test_multiple. Like gdb_test,
gdb_test_multiple recognizes internal errors and unexpected
prompts.
Do not write tests which expect a literal tab character from gdb. On some operating systems (e.g. OpenBSD) the TTY layer expands tabs to spaces, so by the time gdb's output reaches expect the tab is gone.
The source language programs do not need to be in a consistent style. Since gdb is used to debug programs written in many different styles, it's worth having a mix of styles in the testsuite; for instance, some gdb bugs involving the display of source lines would never manifest themselves if the programs used GNU coding style uniformly.
Check the README file, it often has useful information that does not appear anywhere else in the directory.
gdb is a large and complicated program, and if you first starting to work on it, it can be hard to know where to start. Fortunately, if you know how to go about it, there are ways to figure out what is going on.
This manual, the gdb Internals manual, has information which applies generally to many parts of gdb.
Information about particular functions or data structures are located in comments with those functions or data structures. If you run across a function or a global variable which does not have a comment correctly explaining what is does, this can be thought of as a bug in gdb; feel free to submit a bug report, with a suggested comment if you can figure out what the comment should say. If you find a comment which is actually wrong, be especially sure to report that.
Comments explaining the function of macros defined in host, target, or native dependent files can be in several places. Sometimes they are repeated every place the macro is defined. Sometimes they are where the macro is used. Sometimes there is a header file which supplies a default definition of the macro, and the comment is there. This manual also documents all the available macros.
Start with the header files. Once you have some idea of how gdb's internal symbol tables are stored (see symtab.h, gdbtypes.h), you will find it much easier to understand the code which uses and creates those symbol tables.
You may wish to process the information you are getting somehow, to enhance your understanding of it. Summarize it, translate it to another language, add some (perhaps trivial or non-useful) feature to gdb, use the code to predict what a test case would do and write the test case and verify your prediction, etc. If you are reading code and your eyes are starting to glaze over, this is a sign you need to use a more active approach.
Once you have a part of gdb to start with, you can find more
specifically the part you are looking for by stepping through each
function with the next command. Do not use step or you
will quickly get distracted; when the function you are stepping through
calls another function try only to get a big-picture understanding
(perhaps using the comment at the beginning of the function being
called) of what it does. This way you can identify which of the
functions being called by the function you are stepping through is the
one which you are interested in. You may need to examine the data
structures generated at each stage, with reference to the comments in
the header files explaining what the data structures are supposed to
look like.
Of course, this same technique can be used if you are just reading the code, rather than actually stepping through it. The same general principle applies—when the code you are looking at calls something else, just try to understand generally what the code being called does, rather than worrying about all its details.
A good place to start when tracking down some particular area is with
a command which invokes that feature. Suppose you want to know how
single-stepping works. As a gdb user, you know that the
step command invokes single-stepping. The command is invoked
via command tables (see command.h); by convention the function
which actually performs the command is formed by taking the name of
the command and adding `_command', or in the case of an
info subcommand, `_info'. For example, the step
command invokes the step_command function and the info
display command invokes display_info. When this convention is
not followed, you might have to use grep or M-x
tags-search in emacs, or run gdb on itself and set a
breakpoint in execute_command.
If all of the above fail, it may be appropriate to ask for information
on bug-gdb. But never post a generic question like “I was
wondering if anyone could give me some tips about understanding
gdb”—if we had some magic secret we would put it in this manual.
Suggestions for improving the manual are always welcome, of course.
If gdb is limping on your machine, this is the preferred way to get it fully functional. Be warned that in some ancient Unix systems, like Ultrix 4.2, a program can't be running in one process while it is being debugged in another. Rather than typing the command ./gdb ./gdb, which works on Suns and such, you can copy gdb to gdb2 and then type ./gdb ./gdb2.
When you run gdb in the gdb source directory, it will read a
.gdbinit file that sets up some simple things to make debugging
gdb easier. The info command, when executed without a subcommand
in a gdb being debugged by gdb, will pop you back up to the top level
gdb. See .gdbinit for details.
If you use emacs, you will probably want to do a make TAGS after
you configure your distribution; this will put the machine dependent
routines for your local machine where they will be accessed first by
M-.
Also, make sure that you've either compiled gdb with your local cc, or
have run fixincludes if you are compiling with gcc.
Thanks for thinking of offering your changes back to the community of gdb users. In general we like to get well designed enhancements. Thanks also for checking in advance about the best way to transfer the changes.
The gdb maintainers will only install “cleanly designed” patches. This manual summarizes what we believe to be clean design for gdb.
If the maintainers don't have time to put the patch in when it arrives, or if there is any question about a patch, it goes into a large queue with everyone else's patches and bug reports.
The legal issue is that to incorporate substantial changes requires a
copyright assignment from you and/or your employer, granting ownership
of the changes to the Free Software Foundation. You can get the
standard documents for doing this by sending mail to gnu@gnu.org
and asking for it. We recommend that people write in "All programs
owned by the Free Software Foundation" as "NAME OF PROGRAM", so that
changes in many programs (not just gdb, but GAS, Emacs, GCC,
etc) can be
contributed with only one piece of legalese pushed through the
bureaucracy and filed with the FSF. We can't start merging changes until
this paperwork is received by the FSF (their rules, which we follow
since we maintain it for them).
Technically, the easiest way to receive changes is to receive each
feature as a small context diff or unidiff, suitable for patch.
Each message sent to me should include the changes to C code and
header files for a single feature, plus ChangeLog entries for
each directory where files were modified, and diffs for any changes
needed to the manuals (gdb/doc/gdb.texinfo or
gdb/doc/gdbint.texinfo). If there are a lot of changes for a
single feature, they can be split down into multiple messages.
In this way, if we read and like the feature, we can add it to the sources with a single patch command, do some testing, and check it in. If you leave out the ChangeLog, we have to write one. If you leave out the doc, we have to puzzle out what needs documenting. Etc., etc.
The reason to send each change in a separate message is that we will not install some of the changes. They'll be returned to you with questions or comments. If we're doing our job correctly, the message back to you will say what you have to fix in order to make the change acceptable. The reason to have separate messages for separate features is so that the acceptable changes can be installed while one or more changes are being reworked. If multiple features are sent in a single message, we tend to not put in the effort to sort out the acceptable changes from the unacceptable, so none of the features get installed until all are acceptable.
If this sounds painful or authoritarian, well, it is. But we get a lot of bug reports and a lot of patches, and many of them don't get installed because we don't have the time to finish the job that the bug reporter or the contributor could have done. Patches that arrive complete, working, and well designed, tend to get installed on the day they arrive. The others go into a queue and get installed as time permits, which, since the maintainers have many demands to meet, may not be for quite some time.
Please send patches directly to the gdb maintainers.
The script gdb_buildall.sh builds gdb with flag --enable-targets=all set. This builds gdb with all supported targets activated. This helps testing gdb when doing changes that affect more than one architecture and is much faster than using gdb_mbuild.sh.
After building gdb the script checks which architectures are supported and then switches the current architecture to each of those to get information about the architecture. The test results are stored in log files in the directory the script was called from.
An observer is an entity which is interested in being notified when GDB reaches certain states, or certain events occur in GDB. The entity being observed is called the subject. To receive notifications, the observer attaches a callback to the subject. One subject can have several observers.
observer.c implements an internal generic low-level event notification mechanism. This generic event notification mechanism is then re-used to implement the exported high-level notification management routines for all possible notifications.
The current implementation of the generic observer provides support for contextual data. This contextual data is given to the subject when attaching the callback. In return, the subject will provide this contextual data back to the observer as a parameter of the callback.
Note that the current support for the contextual data is only partial, as it lacks a mechanism that would deallocate this data when the callback is detached. This is not a problem so far, as this contextual data is only used internally to hold a function pointer. Later on, if a certain observer needs to provide support for user-level contextual data, then the generic notification mechanism will need to be enhanced to allow the observer to provide a routine to deallocate the data when attaching the callback.
The observer implementation is also currently not reentrant. In particular, it is therefore not possible to call the attach or detach routines during a notification.
Observer notifications can be traced using the command `set debug observer 1' (see Optional messages about internal happenings).
normal_stop Notifications
gdb notifies all normal_stop observers when the
inferior execution has just stopped, the associated messages and
annotations have been printed, and the control is about to be returned
to the user.
Note that the normal_stop notification is not emitted when
the execution stops due to a breakpoint, and this breakpoint has
a condition that is not met. If the breakpoint has any associated
commands list, the commands are executed after the notification
is emitted.
The following interfaces are available to manage observers:
Using the function f, create an observer that is notified when ever event occurs, return the observer.
Remove observer from the list of observers to be notified when event occurs.
The following observable events are defined:
The inferior has stopped for real. The bs argument describes the breakpoints were are stopped at, if any. Second argument print_frame non-zero means display the location where the inferior has stopped.
The target's register contents have changed.
The executable being debugged by GDB has changed: The user decided to debug a different program, or the program he was debugging has been modified since being loaded by the debugger (by being recompiled, for instance).
gdb has just connected to an inferior. For `run', gdb calls this observer while the inferior is still stopped at the entry-point instruction. For `attach' and `core', gdb calls this observer immediately after connecting to the inferior, and before any information on the inferior has been printed.
The shared library specified by solib has been loaded. Note that when gdb calls this observer, the library's symbols probably haven't been loaded yet.
The shared library specified by solib has been unloaded. Note that when gdb calls this observer, the library's symbols have not been unloaded yet, and thus are still available.
The symbol file specified by objfile has been loaded. Called with objfile equal to
NULLto indicate previously loaded symbol table data has now been invalidated.
The thread specified by t has exited. The silent argument indicates that gdb is removing the thread from its tables without wanting to notify the user about it.
An explicit stop request was issued to ptid. If ptid equals minus_one_ptid, the request applied to all threads. If
ptid_is_pid(ptid)returns true, the request applied to all threads of the process pointed at by ptid. Otherwise, the request applied to the single thread pointed at by ptid.
The target was resumed. The ptid parameter specifies which thread was resume, and may be RESUME_ALL if all threads are resumed.
A new breakpoint has been created. The argument bpnum is the number of the newly-created breakpoint.
A breakpoint has been destroyed. The argument bpnum is the number of the newly-destroyed breakpoint.
A breakpoint has been modified in some way. The argument bpnum is the number of the modified breakpoint.
A new tracepoint has been created. The argument tpnum is the number of the newly-created tracepoint.
A tracepoint has been destroyed. The argument tpnum is the number of the newly-destroyed tracepoint.
A tracepoint has been modified in some way. The argument tpnum is the number of the modified tracepoint.
The current architecture has changed. The argument newarch is a pointer to the new architecture.
The thread's ptid has changed. The old_ptid parameter specifies the old value, and new_ptid specifies the new value.
The inferior inf has been added to the list of inferiors. At this point, it might not be associated with any process.
The inferior identified by inf has been attached to a process.
Either the inferior associated with inf has been detached from the process, or the process has exited.
The inferior inf has been removed from the list of inferiors. This method is called immediately before freeing inf.
Bytes from data to data + len have been written to the current inferior at addr.
This observer is used for internal testing. Do not use. See testsuite/gdb.gdb/observer.exp.
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
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A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.
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_initialize_arch_tdep: Adding a New Target_initialize_arch_tdep: How an Architecture is Represented_initialize_language: Language Supporta.out format: Symbol Handlingabout_to_proceed: GDB Observersadd_cmd: User Interfaceadd_com: User Interfaceadd_setshow_cmd: User Interfaceadd_setshow_cmd_full: User Interfaceadd_symtab_fns: Symbol Handlingaddress_class_name_to_type_flags: Defining Other Architecture Featuresaddress_class_name_to_type_flags_p: Defining Other Architecture Featuresalign_down: Functions and Variable to Analyze Framesalign_up: Functions and Variable to Analyze Framesallocate_symtab: Language Supportarchitecture_changed: GDB Observersbfd_arch_info: Looking Up an Existing ArchitectureBIG_BREAKPOINT: Defining Other Architecture FeaturesBPT_VECTOR: Defining Other Architecture FeaturesBREAKPOINT: Defining Other Architecture Featuresbreakpoint_created: GDB Observersbreakpoint_deleted: GDB Observersbreakpoint_modified: GDB Observersbug-gdb mailing list: Getting StartedCC_HAS_LONG_LONG: Host Definitioncore_addr_greaterthan: Functions and Variable to Analyze Framescore_addr_lessthan: Functions and Variable to Analyze FramesCRLF_SOURCE_FILES: Host Definitioncurrent_language: Language SupportDEFAULT_PROMPT: Host Definitiondeprecate_cmd: User InterfaceDEPRECATED_IBM6000_TARGET: Defining Other Architecture FeaturesDEV_TTY: Host DefinitionDIRNAME_SEPARATOR: Misc GuidelinesDISABLE_UNSETTABLE_BREAK: Defining Other Architecture Featuresdiscard_cleanups: Misc Guidelinesdo_cleanups: Misc Guidelinesevaluate_subexp: Language Supportexecutable_changed: GDB Observersextract_typed_address: Pointers and AddressesFILENAME_CMP: Misc Guidelinesfind_pc_function: Symbol Handlingfind_pc_line: Symbol Handlingfind_sym_fns: Symbol Handlinggdbarch structure: OS ABI Variant HandlingFOPEN_RB: Host Definitionfp0_regnum: Register Architecture Functions & Variablesframe_align: Functions and Variable to Analyze Framesframe_base: Analyzing Stacks---Frame Sniffersframe_base_append_sniffer: Analyzing Stacks---Frame Sniffersframe_base_set_default: Analyzing Stacks---Frame Sniffersframe_num_args: Functions to Access Frame Dataframe_red_zone_size: Functions and Variable to Analyze Framesframe_register_unwind: Stack Framesframe_unwind: Analyzing Stacks---Frame Sniffersframe_unwind_append_sniffer: Analyzing Stacks---Frame Sniffersframe_unwind_append_unwinder: Stack Framesframe_unwind_got_address: Stack Framesframe_unwind_got_constant: Stack Framesframe_unwind_got_memory: Stack Framesframe_unwind_got_optimized: Stack Framesframe_unwind_got_register: Stack Framesframe_unwind_prepend_unwinder: Stack FramesGCC2_COMPILED_FLAG_SYMBOL: Defining Other Architecture FeaturesGCC_COMPILED_FLAG_SYMBOL: Defining Other Architecture Featuresgdb_byte: Register CachingGDB_OSABI_AIX: OS ABI Variant HandlingGDB_OSABI_CYGWIN: OS ABI Variant HandlingGDB_OSABI_FREEBSD_AOUT: OS ABI Variant HandlingGDB_OSABI_FREEBSD_ELF: OS ABI Variant HandlingGDB_OSABI_GO32: OS ABI Variant HandlingGDB_OSABI_HPUX_ELF: OS ABI Variant HandlingGDB_OSABI_HPUX_SOM: OS ABI Variant HandlingGDB_OSABI_HURD: OS ABI Variant HandlingGDB_OSABI_INTERIX: OS ABI Variant HandlingGDB_OSABI_IRIX: OS ABI Variant HandlingGDB_OSABI_LINUX: OS ABI Variant HandlingGDB_OSABI_NETBSD_AOUT: OS ABI Variant HandlingGDB_OSABI_NETBSD_ELF: OS ABI Variant HandlingGDB_OSABI_OPENBSD_ELF: OS ABI Variant HandlingGDB_OSABI_OSF1: OS ABI Variant HandlingGDB_OSABI_QNXNTO: OS ABI Variant HandlingGDB_OSABI_SOLARIS: OS ABI Variant HandlingGDB_OSABI_SVR4: OS ABI Variant HandlingGDB_OSABI_UNINITIALIZED: OS ABI Variant HandlingGDB_OSABI_UNKNOWN: OS ABI Variant HandlingGDB_OSABI_WINCE: OS ABI Variant Handlinggdbarch: How an Architecture is Representedgdbarch accessor functions: Creating a New Architecturegdbarch lookup: Looking Up an Existing Architecturegdbarch register architecture functions: Register Architecture Functions & Variablesgdbarch register information functions: Register Information Functionsgdbarch_addr_bits_remove: Defining Other Architecture Featuresgdbarch_address_class_name_to_type_flags: Address Classesgdbarch_address_class_type_flags: Defining Other Architecture Featuresgdbarch_address_class_type_flags: Address Classesgdbarch_address_class_type_flags_p: Defining Other Architecture Featuresgdbarch_address_class_type_flags_to_name: Defining Other Architecture Featuresgdbarch_address_class_type_flags_to_name: Address Classesgdbarch_address_class_type_flags_to_name_p: Defining Other Architecture Featuresgdbarch_address_to_pointer: Defining Other Architecture Featuresgdbarch_address_to_pointer: Pointers and Addressesgdbarch_adjust_breakpoint_address: Defining Other Architecture Featuresgdbarch_alloc: Creating a New Architecturegdbarch_believe_pcc_promotion: Defining Other Architecture Featuresgdbarch_bits_big_endian: Defining Other Architecture Featuresgdbarch_breakpoint_from_pc: Defining Other Architecture Featuresgdbarch_call_dummy_location: Defining Other Architecture Featuresgdbarch_cannot_fetch_register: Defining Other Architecture Featuresgdbarch_cannot_store_register: Defining Other Architecture Featuresgdbarch_char_signed: Defining Other Architecture Featuresgdbarch_convert_register_p: Defining Other Architecture Featuresgdbarch_convert_register_p: Register and Memory Datagdbarch_data: Misc Guidelinesgdbarch_data_register_post_init: Misc Guidelinesgdbarch_data_register_pre_init: Misc Guidelinesgdbarch_decr_pc_after_break: Defining Other Architecture Featuresgdbarch_deprecated_fp_regnum: Defining Other Architecture Featuresgdbarch_double_bit: Defining Other Architecture Featuresgdbarch_dummy_id: Defining Other Architecture Featuresgdbarch_dwarf2_reg_to_regnum: Defining Other Architecture Featuresgdbarch_ecoff_reg_to_regnum: Defining Other Architecture Featuresgdbarch_float_bit: Defining Other Architecture Featuresgdbarch_fp0_regnum: Defining Other Architecture Featuresgdbarch_get_longjmp_target: Defining Other Architecture Featuresgdbarch_get_longjmp_target: Algorithmsgdbarch_have_nonsteppable_watchpoint: Algorithmsgdbarch_in_function_epilogue_p: Defining Other Architecture Featuresgdbarch_in_solib_return_trampoline: Defining Other Architecture Featuresgdbarch_info: Looking Up an Existing Architecturegdbarch_init_osabi: OS ABI Variant Handlinggdbarch_int_bit: Defining Other Architecture Featuresgdbarch_integer_to_address: Defining Other Architecture Featuresgdbarch_list_lookup_by_info: Looking Up an Existing Architecturegdbarch_long_bit: Defining Other Architecture Featuresgdbarch_long_double_bit: Defining Other Architecture Featuresgdbarch_long_long_bit: Defining Other Architecture Featuresgdbarch_lookup_osabi: OS ABI Variant Handlinggdbarch_memory_insert_breakpoint: Defining Other Architecture Featuresgdbarch_memory_remove_breakpoint: Defining Other Architecture Featuresgdbarch_osabi_name: OS ABI Variant Handlinggdbarch_pointer_to_address: Defining Other Architecture Featuresgdbarch_pointer_to_address: Pointers and Addressesgdbarch_print_insn: Defining Other Architecture Featuresgdbarch_ptr_bit: Defining Other Architecture Featuresgdbarch_push_dummy_call: Defining Other Architecture Featuresgdbarch_push_dummy_code: Defining Other Architecture Featuresgdbarch_register: Adding a New Targetgdbarch_register: How an Architecture is Representedgdbarch_register_osabi: OS ABI Variant Handlinggdbarch_register_osabi_sniffer: OS ABI Variant Handlinggdbarch_register_to_value: Defining Other Architecture Featuresgdbarch_register_to_value: Register and Memory Datagdbarch_return_value: Defining Other Architecture Featuresgdbarch_sdb_reg_to_regnum: Defining Other Architecture Featuresgdbarch_short_bit: Defining Other Architecture Featuresgdbarch_skip_permanent_breakpoint: Defining Other Architecture Featuresgdbarch_skip_trampoline_code: Defining Other Architecture Featuresgdbarch_stab_reg_to_regnum: Defining Other Architecture Featuresgdbarch_stabs_argument_has_addr: Defining Other Architecture Featuresgdbarch_tdep definition: Creating a New Architecturegdbarch_tdep when allocating new gdbarch: Creating a New Architecturegdbarch_value_to_register: Defining Other Architecture Featuresgdbarch_value_to_register: Register and Memory Datagdbarch_virtual_frame_pointer: Defining Other Architecture FeaturesINIT_FILENAME: Host Definitiongeneric_elf_osabi_sniff_abi_tag_sections: OS ABI Variant Handlingget_frame_register: Stack Framesget_frame_type: Stack FramesHAVE_CONTINUABLE_WATCHPOINT: AlgorithmsHAVE_DOS_BASED_FILE_SYSTEM: Misc GuidelinesHAVE_STEPPABLE_WATCHPOINT: Algorithmsi386_cleanup_dregs: AlgorithmsI386_DR_LOW_GET_STATUS: AlgorithmsI386_DR_LOW_RESET_ADDR: AlgorithmsI386_DR_LOW_SET_ADDR: AlgorithmsI386_DR_LOW_SET_CONTROL: Algorithmsi386_insert_hw_breakpoint: Algorithmsi386_insert_watchpoint: Algorithmsi386_region_ok_for_watchpoint: Algorithmsi386_remove_hw_breakpoint: Algorithmsi386_remove_watchpoint: Algorithmsi386_stopped_by_watchpoint: Algorithmsi386_stopped_data_address: AlgorithmsI386_USE_GENERIC_WATCHPOINTS: Algorithmsin_dynsym_resolve_code: Defining Other Architecture Featuresinferior_added: GDB Observersinferior_appeared: GDB Observersinferior_created: GDB Observersinferior_exit: GDB Observersinferior_removed: GDB Observersinner_than: Functions and Variable to Analyze FramesIS_ABSOLUTE_PATH: Misc GuidelinesIS_DIR_SEPARATOR: Misc GuidelinesISATTY: Host Definitionlength_of_subexp: Language Supportlibgdb: libgdblibiberty library: Support Librarieslint: Host DefinitionLITTLE_BREAKPOINT: Defining Other Architecture Featureslong long data type: Host Definitionlongjmp debugging: AlgorithmsLSEEK_NOT_LINEAR: Host Definitionlval_type enumeration, for values.: Valuesmake_cleanup: Misc Guidelinesmake_cleanup_ui_out_list_begin_end: User Interfacemake_cleanup_ui_out_tuple_begin_end: User Interfacememory_changed: GDB ObserversNATDEPFILES: Native Debuggingui_out functions: User Interfacenew_objfile: GDB Observersnew_thread: GDB Observersnormal_stop: GDB Observersnormal_stop observer: GDB Observersobstacks: Support Librariesop_print_tab: Language Supportparse_exp_1: Language Supportpc_regnum: Register Architecture Functions & Variablesprefixify_subexp: Language Supportprint_float_info: Register Information Functionsprint_registers_info: Register Information Functionsprint_subexp: Language Supportprint_vector_info: Register Information FunctionsPRINTF_HAS_LONG_LONG: Host Definitionps_regnum: Register Architecture Functions & Variablespseudo_register_read: Register Architecture Functions & Variablespseudo_register_write: Register Architecture Functions & Variablespush_dummy_call: Functions Creating Dummy Framespush_dummy_code: Functions Creating Dummy Framesread_pc: Register Architecture Functions & Variablesregcache_cooked_read: Register Cachingregcache_cooked_read_signed: Register Cachingregcache_cooked_read_unsigned: Register Cachingregcache_cooked_write: Register Cachingregcache_cooked_write_signed: Register Cachingregcache_cooked_write_unsigned: Register CachingREGISTER_CONVERT_TO_RAW: Defining Other Architecture FeaturesREGISTER_CONVERT_TO_VIRTUAL: Defining Other Architecture Featuresregister_name: Register Information Functionsregister_reggroup_p: Register Information Functionsregister_type: Register Information Functionsregset_from_core_section: Defining Other Architecture FeaturesREMOTE_BPT_VECTOR: Defining Other Architecture FeaturesSENTINEL_FRAME: Stack Framesset_gdbarch functions: Creating a New Architectureset_gdbarch_bits_big_endian: Defining Other Architecture Featuresset_gdbarch_sofun_address_maybe_missing: Defining Other Architecture FeaturesSIGWINCH_HANDLER: Host DefinitionSIGWINCH_HANDLER_BODY: Host Definitionskip_prologue: Functions and Variable to Analyze FramesSKIP_SOLIB_RESOLVER: Defining Other Architecture FeaturesSLASH_STRING: Misc GuidelinesSOFTWARE_SINGLE_STEP: Defining Other Architecture FeaturesSOFTWARE_SINGLE_STEP_P: Defining Other Architecture FeaturesSOLIB_ADD: Native DebuggingSOLIB_CREATE_INFERIOR_HOOK: Native Debuggingsolib_loaded: GDB Observerssolib_unloaded: GDB Observerssp_regnum: Register Architecture Functions & VariablesSTART_INFERIOR_TRAPS_EXPECTED: Native DebuggingSTOPPED_BY_WATCHPOINT: Algorithmsstore_typed_address: Pointers and Addressesstruct: GDB Observersstruct gdbarch creation: Creating a New Architecturestruct regcache: Register Cachingstruct value, converting register contents to: Register and Memory Datasym_fns structure: Symbol HandlingSYMBOL_RELOADING_DEFAULT: Defining Other Architecture FeaturesTARGET_CAN_USE_HARDWARE_WATCHPOINT: Algorithmstarget_changed: GDB ObserversTARGET_CHAR_BIT: Defining Other Architecture Featurestarget_insert_breakpoint: Algorithmstarget_insert_hw_breakpoint: Algorithmstarget_insert_watchpoint: AlgorithmsTARGET_REGION_OK_FOR_HW_WATCHPOINT: Algorithmstarget_remove_breakpoint: Algorithmstarget_remove_hw_breakpoint: Algorithmstarget_remove_watchpoint: Algorithmstarget_resumed: GDB Observerstarget_stopped_data_address: Algorithmstarget_watchpoint_addr_within_range: Algorithmstest_notification: GDB Observersthread_exit: GDB Observersthread_ptid_changed: GDB Observersthread_stop_requested: GDB Observerstracepoint_created: GDB Observerstracepoint_deleted: GDB Observerstracepoint_modified: GDB Observersui_out functions: User Interfaceui_out functions, usage examples: User Interfaceui_out_field_core_addr: User Interfaceui_out_field_fmt: User Interfaceui_out_field_fmt_int: User Interfaceui_out_field_int: User Interfaceui_out_field_skip: User Interfaceui_out_field_stream: User Interfaceui_out_field_string: User Interfaceui_out_flush: User Interfaceui_out_list_begin: User Interfaceui_out_list_end: User Interfaceui_out_message: User Interfaceui_out_spaces: User Interfaceui_out_stream_delete: User Interfaceui_out_stream_new: User Interfaceui_out_table_begin: User Interfaceui_out_table_body: User Interfaceui_out_table_end: User Interfaceui_out_table_header: User Interfaceui_out_text: User Interfaceui_out_tuple_begin: User Interfaceui_out_tuple_end: User Interfaceui_out_wrap_hint: User Interfaceunwind_dummy_id: Functions Creating Dummy Framesunwind_pc: Functions to Access Frame Dataunwind_sp: Functions to Access Frame Dataui_out functions: User Interfacevalue structure: Valuesvalue_as_address: Pointers and Addressesvalue_from_pointer: Pointers and Addressesvoid: GDB Observersvolatile: Host Definitionwrap_here: Misc Guidelineswrite_pc: Register Architecture Functions & Variables[1] The function cast is not portable ISO C.
[2] As of this writing (April 2001),
setting verbosity level is not yet implemented, and is always returned
as zero. So calling ui_out_message with a verbosity
argument more than zero will cause the message to never be printed.
[3] Some D10V instructions are actually pairs of 16-bit sub-instructions. However, since you can't jump into the middle of such a pair, code addresses can only refer to full 32 bit instructions, which is what matters in this explanation.
[4]
Historically, gdb always had a concept of a frame pointer
register, which could be accessed via the gdb variable,
$fp. That concept is now deprecated, recognizing that not all
architectures have a frame pointer. However if an architecture does
have a frame pointer register, and defines a register or
pseudo-register with the name "fp", then that register will be
used as the value of the $fp variable.
[5] This is a simplified example for illustrative purposes only. Good optimizing compilers would not put anything on the stack for such simple functions. Indeed they might eliminate the recursion and use of the stack entirely!
[6] It is worth noting that if it cannot be determined in any
other way (for example by there being a register with the name
"fp"), then the result of the this_base function will be
used as the value of the frame pointer variable $fp in
gdb. This is very often not correct (for example with the
OpenRISC 1000, this value is the stack pointer, $sp). In this
case a register (raw or pseudo) with the name "fp" should be
defined. It will be used in preference as the value of $fp.
[7] If you are using a board file, it could override the test-suite default; search the board file for "timeout".