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Function Calls and Assembly

Im trying to understand how a program makes a function call (using C semantics) with assembly x86 code. Any help would be greatly appreciated.

I could not find any sources to specifically answer this question.

Solution

  • In x86, there are the instructions called call and ret to do this. call store the current address on stack and jmp to a label passed as argument. And the instruction called ret pop this address and jump to it after add one byte to that address.

    Code example:

    C

    int sum(int a, int b)
{
  return a + b;
}

void f(void)
{
  sum(2, 2);
  g();
}

    A compiler might generate(x86-assembly-like example):

    f:
  push 2
  push 2
  call sum
  call g
  ret

sum:
   pop eax
   pop ebx
   add eax, ebx
   ret

    I hope it helps