10.11. 汇编语言¶

寄存器:

rbp: register base pointer 栈基址寄存器（栈帧指针），指向当前栈帧的(栈底)地址
    rbp is the base pointer, which points to the base of the current stack frame
rsp: register stack pointer 栈顶寄存器（栈指针），指向当前栈帧的(栈顶)地址
    rsp is the stack pointer, which points to the top of the current stack frame.

10.11.1. 实例-函数调用¶

C 语言:

// function_example.c
#include <stdio.h>
int static add(int a, int b)
{
    return a+b;
}
int main()
{
    int x = 5;
    int y = 10;
    int u = add(x, y);
}

执行命令:

$ gcc -g -c function_example.c
$ objdump -d -M intel -S function_example.o

汇编代码-add:

int static add(int a, int b)
{
   0:   55                      push   rbp
   1:   48 89 e5                mov    rbp,rsp
   4:   89 7d fc                mov    DWORD PTR [rbp-0x4],edi
   7:   89 75 f8                mov    DWORD PTR [rbp-0x8],esi
    return a+b;
   a:   8b 55 fc                mov    edx,DWORD PTR [rbp-0x4]
   d:   8b 45 f8                mov    eax,DWORD PTR [rbp-0x8]
  10:   01 d0                   add    eax,edx
}
  12:   5d                      pop    rbp
  13:   c3                      ret

说明:

push   rbp:
    把之前调用函数，也就是 main 函数的栈帧的栈底地址，压栈
mov    rbp,rsp:
    把 rsp 的值复制到 rbp 里，而 rsp 始终会指向栈顶
    这意味着：rbp 和 rsp 都指向 main 函数的栈顶
    也就是 add 函数的栈帧的栈底地址了

汇编代码-main:

0000000000000014 <main>:
int main()
{
  14:   55                      push   rbp
  15:   48 89 e5                mov    rbp,rsp
  18:   48 83 ec 10             sub    rsp,0x10
    int x = 5;
  1c:   c7 45 fc 05 00 00 00    mov    DWORD PTR [rbp-0x4],0x5
    int y = 10;
  23:   c7 45 f8 0a 00 00 00    mov    DWORD PTR [rbp-0x8],0xa
    int u = add(x, y);
  2a:   8b 55 f8                mov    edx,DWORD PTR [rbp-0x8]
  2d:   8b 45 fc                mov    eax,DWORD PTR [rbp-0x4]
  30:   89 d6                   mov    esi,edx
  32:   89 c7                   mov    edi,eax
  34:   e8 c7 ff ff ff          call   0 <add>
  39:   89 45 f4                mov    DWORD PTR [rbp-0xc],eax
  3c:   b8 00 00 00 00          mov    eax,0x0
}
  41:   c9                      leave
  42:   c3                      ret

内联优化编译:

$ gcc -g -c -O function_example_inline.c
$ objdump -d -M intel -S function_example_inline.o