👀 Views: 92 💬 Answers: 1 📅 Created: 2025-06-04

assembly gcc inline-assembly C

I'm not sure how to approach I need some guidance on I'm experiencing stack corruption issues while trying to integrate inline assembly into my C code using GCC on an x86_64 platform. The scenario arises when I use inline assembly to perform some arithmetic operations and then call a function afterwards. I'm seeing strange behaviors, like incorrect return values and, in some cases, segmentation faults. Here's a simplified version of my code: ```c #include <stdio.h> void add(int a, int b) { int result; asm volatile ( "addl %%ebx, %%eax" : "=a"(result) : "a"(a), "b"(b) ); printf("Result: %d\n", result); } int main() { add(5, 10); return 0; } ``` When I compile this using `gcc -m64 -o test test.c`, it runs fine, but if I change the parameters in the `add` function to something larger or modify the assembly to include more operations, such as a loop, I encounter issues. For instance, when I modify it to: ```c void add(int a, int b) { int result; asm volatile ( "movl %%eax, %%ecx\n" "loop Start\n" "addl %%ebx, %%eax\n" "dec %%ecx\n" "Start:\n" : "=a"(result) : "a"(a), "b"(b), "c"(5) ); printf("Result: %d\n", result); } ``` Now, when calling `add(5, 10);`, it often crashes with a segmentation fault. I've checked that the loop counter is correctly initialized, but I suspect something's going wrong due to the inline assembly manipulating registers in a way that affects the stack. I've also tried adding a `clobber` list to specify that I’m using `ecx`, but it didn't help. What could be causing this stack corruption, and how can I effectively manage the registers to prevent such issues? This is part of a larger service I'm building. I'd be grateful for any help.