gcc编译c语言中内嵌汇编 - fifan的专栏 - CSDNBlog

cc编译c语言中内嵌汇编
--AT&T and Intel 汇编语法对照
寄存器命名：
AT&T:  %eax
Intel: eax
AT&T 语法源地址在左侧，目的地址在右侧与Intel 方式语法相反
将eax值传入ebx
AT&T:  movl %eax, %ebx
Intel: mov ebx, eax
AT&T 语法在立即数前有前缀$.
AT&T:  movl $0x0h, %eax
Intel: mov eax,0x0h
AT&T 语法在操作符后跟表示操作数类型的后缀b,w,l分别表示字节，字，双字，相当于伪操作符ptr，如果不加的话GAS会guess
AT&T:  movw %ax, %bx
Intel: mov bx, ax
内存寻址方式
AT&T:  immed32(basepointer,indexpointer,indexscale)
Intel: [basepointer + indexpointer*indexscale + immed32]
地址计算公式为：
immed32 + basepointer + indexpointer * indexscale
直接寻址
AT&T:  _a
Intel: [_a]
间接寻址
AT&T:  (%eax)
Intel: [eax]
相对寻址
AT&T: _variable(%eax)
Intel: [eax + _variable]
AT&T:  _array(,%eax,4)
Intel: [eax*4 + array]
C 代码: *(p+1) p定义为char *
AT&T:  1(%eax) where eax has the value of p
Intel: [eax + 1]
结构体数组寻址，结构体长度为8，下标存于eax，结构体内偏移地址存于ebx，_array为结构体数组首地址
AT&T:  _array(%ebx,%eax,8)
Intel: [ebx + eax*8 + _array]
函数内部实现交换
1、输入与输出变量相同
汇编代码部分标准的交换实现，输入部分用0寄存器表示"=r"(a)中所指定的寄存器即输入与输出变量相同
int main()
{                                                         　　                   804842c:      mov    0xfffffff4(%ebp),%ecx
int a = 10, b = 0;                                                    804842f:      mov    0xfffffff0(%ebp),%edx
printf("before swap: a = %2d, b = %2d\n", a , b);   8048432:      mov    %ecx,%ebx
__asm__("nop;                                                      8048434:      mov    %edx,%esi
movl %0, %%eax;                                        8048436:      nop
movl %1, %0;                                              8048437:      mov    %ebx,%eax
movl %%eax, %1;                                        8048439:      mov    %esi,%ebx
nop;"                                                            804843b:      mov    %eax,%esi
:                                                                    804843d:      nop
"=r"(a), "=r"(b)                                             804843e:      mov    %ebx,%edx
:                                                                    8048440:      mov    %esi,%ecx
"0"(a), "1"(b)                                                8048442:      mov    %edx,%eax
:                                                                    8048444:      mov    %eax,0xfffffff4(%ebp)
"%eax"                                                         8048447:      mov    %ecx,%eax
);                                                                   8048449:      mov    %eax,0xfffffff0(%ebp)
printf("after  swap: a = %2d, b = %2d\n", a, b);
return 0;
}
2、输入与输出用不同的寄存器，&表示输入输出需要分配不同的寄存器
int main()
{
int a = 10, b = 0;
printf("before swap: a = %2d, b = %2d\n", a, b);          804842b:      mov    0xfffffff8(%ebp),%edx
__asm__("nop;                                                            804842e:     mov    0xfffffff4(%ebp),%eax
movl %2,%1;                                                     8048431:     nop
movl %3,%0;                                                     8048432:     mov    %edx,%ebx
nop;"                                                                  8048434:      mov    %eax,%ecx
:                                                                          8048436:      nop
"=&r"(a), "=&r"(b)                                             8048437:      mov    %ecx,%eax
:                                                                          8048439:      mov    %ebx,%edx
"r"(a), "r"(b)                                                       804843b:      mov    %eax,%eax
);                                                                        804843d:      mov    %eax,0xfffffff8(%ebp)
printf("after  swap: a = %2d, b = %2d\n", a , b);           8048440:      mov    %edx,%eax
return0;                                                                      8048442:      mov    %eax,0xfffffff4(%ebp)
}
3、交换函数，需要间接寻址
#include
void swap(int* x, int* y)     08048400 :
{                                                                                          8048400:      push   %ebp
__asm__("nop;                                                             8048401:      mov    %esp,%ebp
movl (%0), %%eax;                                            8048403:      push   %ebx
movl (%1), %%ebx;                                            8048404:      mov    0x8(%ebp),%ecx
movl %%ebx, (%0);                                            8048407:      mov    0xc(%ebp),%edx
movl %%eax, (%1);                                            804840a:      nop
nop;"                                                                   804840b:      mov    (%ecx),%eax
:                                                                           804840d:      mov    (%edx),%ebx
:                                                                           804840f:      mov    %ebx,(%ecx)
"r"(x),"r"(y)                                                          8048411:      mov    %eax,(%edx)
:                                                                           8048413:      nop
"eax", "ebx", "memory"                                        8048414:      mov    (%esp,1),%ebx ;ebx还原
);                                                                         8048417:     leave   ;movl %ebp, %esp; pop ebp
}                                                                                         8048418:      ret
8048419:      lea    0x0(%esi),%esi
int main()
{
int a = 10, b = 0;
printf("before swap: a = %2d, b = %2d\n", a, b);
swap(&a, &b);
printf("after  swap: a = %2d, b = %2d\n", a, b);
return 0;
}
4、从汇编代码中分离函数
1> 获得汇编代码
这里用加法函数，源代码为：
int sum(int a, int b)
{
int c = a + b;
return c;
}
对应的汇编代码为
Disassembly of           section .text:
00000000 :
0:   55                        push   %ebp
1:   89 e5                   mov    %esp,%ebp
3:   83 ec 04              sub    $0x4,%esp
6:   8b 45 0c              mov    0xc(%ebp),%eax
9:   03 45 08              add    0x8(%ebp),%eax
c:   89 45 fc               mov    %eax,0xfffffffc(%ebp)
f:   8b 45 fc                mov    0xfffffffc(%ebp),%eax
12:   89 c0                  mov    %eax,%eax
14:   c9                       leave
15:   c3                       ret
16:   89 f6                   mov    %esi,%esi
2> 编写内嵌汇编语言函数
分析：为函数构建运行时堆栈情况即可使其顺利运行，由于编译器在函数执行开始和结束时会增加
routine begin：
push %ebp; mov %esp, %ebp
routine end:
leave; ret
将上面的0, 1, 14, 15去掉，返回参数放在eax中将输出部分设置为"=a"(r) 用eax寄存器 r 为需要的return type
步骤：
i   定义return_type r 变量
ii  去掉push %ebp; mov %esp, %ebp;   leave; ret
iii 输出部分为:"=a"(r):
$ vi sumassemble.c
int sum(int a, int b)
{
int r;
__asm__("sub $0x4, %%esp;
movl 0xc(%%ebp), %%eax;
addl 0x8(%%ebp), %%eax;
movl %%eax, 0xfffffffc(%%ebp);
movl 0xfffffffc(%%ebp), %%eax;
movl %%eax, %%eax;"
:
"=a"(r)
);
return r;
}
Disassembly of           section .text:
00000000 :
0:   55                        push   %ebp
1:   89 e5                   mov    %esp,%ebp
3:   83 ec 04              sub    $0x4,%esp
6:   83 ec 04              sub    $0x4,%esp
9:   8b 45 0c              mov    0xc(%ebp),%eax
c:   03 45 08              add    0x8(%ebp),%eax
f:   89 45 fc                mov    %eax,0xfffffffc(%ebp)
12:   8b 45 fc              mov    0xfffffffc(%ebp),%eax
15:   89 c0                  mov    %eax,%eax
17:   89 c0                  mov    %eax,%eax
19:   89 45 fc              mov    %eax,0xfffffffc(%ebp)
1c:   8b 45 fc              mov    0xfffffffc(%ebp),%eax
1f:   89 c0                   mov    %eax,%eax
21:   c9                       leave
22:   c3                       ret
23:   90                       nop
3> 编译可执行程序
$ vi summain.c
extern int sum(int ,int);
int main()
{
int x = sum(1,2);
printf("x = %d\n", x);
return 0;
}
$ cc -o sum_main sum_main.c sum_assemble.c
$ ./sum_main
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