All Questions
72 questions
1
vote
1
answer
134
views
What is the reasoning behind this boilerplate start-up code?
Here's a snippet from disassembled output of a simple program with gcc on Linux:
400478: ff 15 6a 0b 20 00 callq *0x200b6a(%rip) # 600fe8 <__libc_start_main@GLIBC_2.2.5>
...
- 1,269
2
votes
0
answers
77
views
Load function written in amd64 assembly into memory and call it
I am trying to write a small jit compiler. For that, I need to somehow load new code into memory and then execute it.
Given the output of the compiler for a function that simply adds the 2nd and 3rd ...
- 396
0
votes
0
answers
115
views
Why does accessing an initialised array cause a segfault?
I'm making a compiler for brainfuck and I've made the ELF header and 2 program headers, the relevant header is this:
Program_Header dataHeader =
{
1, ...
- 9
0
votes
1
answer
326
views
ld warning from custom compiler: ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000
When trying to actually use my custom compiler for a made up language I get the following warning from ld: "ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000" it ...
user18591665
1
vote
0
answers
119
views
Why does the compiler need the intermediate representations for link time optimization?
My professor mentioned that gcc can be run with -flto. I am wondering why the intermediary (GIMPLE in GCC case) are needed.
Why is the assembly not sufficient?
He mentioned that this allows the ...
0
votes
0
answers
26
views
How does (SIC) assembler print hash tables? [duplicate]
I am trying to make an assembler in C for the SIC architecture.
And I saw that symbol table and object code table are usually made with hash tables.
What I wonder is, how assemblers print these tables....
- 23
1
vote
0
answers
724
views
Why does riscv32-gcc use LI and ADDI to put a 32-bit constant in a register, not LI with the full constant?
....
//---------------------------------
// Init State
//---------------------------------
int32_t state[16];
state[0] = 0x61707865;
...
|| c -> asm(riscv32-gcc -S inputcode.c)
|| ...
- 21
0
votes
0
answers
217
views
How does the C compiler know memory location even though the program gets loaded in memory after the compilation phase? [duplicate]
Generally, there are 2 phases of the program - compiling and running.
Compile-time - compiler generates assembly of source program something like this -
MOV R1 R2
LOAD R2 1000
Run Time - program gets ...
1
vote
0
answers
842
views
Why does this assembly cause a segmentation fault? [duplicate]
I'm working on a hobby compiler project, and am getting frustrated because my generated assembly makes perfect sense to me but causes a segmentation fault on running. For the input printf("%d&...
- 1,076
1
vote
0
answers
192
views
Why "a==b" in C is compiled to "xor; j; sltu" in assembly? - Why instruction after unconditional jump? [duplicate]
I want to see how == is compiled in C. Thus I try a simple code:
#include <stdio.h>
int f(int a,int b) {
return a==b; // NOTE THIS
}
int main(void) {
int a,b,c;
scanf("%d"...
- 17.7k
2
votes
2
answers
141
views
How does the compiler differentiate indentically-named items
In the following example:
int main(void) {
int a=7;
{
int a=8;
}
}
The generated assembly would be something like this (from Compiler Explorer) without optimizations:
main:
...
- 4,837
3
votes
1
answer
187
views
How do nested scopes affect stack depth?
I tried compiling the following c-code using MSVC into assembly both with (CL TestFile.c /Fa /Ot) and without optimizations (CL TestFile.c /Fa) and the result is they produce the same stack-depth.
Why ...
1
vote
2
answers
440
views
How does format specifiers works in compiler?
Take the C language as an example for this question. In the C language we can see many format specifiers, such as %i %d %c %s %f etc. In the compilation process, the C code is converted into an ...
1
vote
1
answer
1k
views
Why does C compile to assembly instead of binary? [duplicate]
What is the advantage of C compiling to assembly instead of binary as all I can think of are disadvantages such as making compilation slower?
2
votes
0
answers
240
views
reference to external function in disassembly code [duplicate]
I am trying to see everything in big picture regarding compilation and linking.
I have below simple function implemented in add_caller.c :
extern int add(int a, int b);
int
main(int argc, char **...
- 1,346