Question

I’m using GCC with the -fomit-frame-pointer and -O2 options. When I looked through the assembly code it generated,

push %ebp
movl %esp, %ebp

at the start and pop %ebp at the end is removed. But some redundant subl/addl instructions to esp is left in – subl $12, %esp at the start and addl $12, %esp at the end.

How will I be able to remove them as some inline assembly will jmp to another function before addl is excecuted.

Answer 1

I solved the problem by giving a function prototype, then defining it manually like this:

void my_function();

asm (
    ".globl _my_function\n"
"_my_function:\n\t"
/* Assembler instructions go here */
);

Later I also wanted the function to be exported, so I added this at the end of the source file:

asm (
    ".section  .drectve\n\t"
    ".ascii \" -export:my_function\"\n"
);