2 函数的参数传递

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李延 LV6 2022-06-07

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# 1 说明

在前面章节中，我们知道参数传递时通过6个寄存器进行传递的。当大于6个字符是，会通过栈进行传递。

# 2 参数小于6个

```c
#include <stdio.h>

int sum(int a1,int a2,int a3,int a4,int a5,int a6){
    return a1+a2+a3+a4+a5+a6;
}

int main() {
    int num = sum(1,2,3,4,5,6);

printf("sum is %d!\n",num);
    return 0;
}
```

```asm
    .file  "parameter.c"
   .text
   .globl sum
   .type  sum, @function
sum:
.LFB11:
   .cfi_startproc
   addl   %esi, %edi
   addl   %edi, %edx
   addl   %edx, %ecx
   addl   %ecx, %r8d
   leal   (%r8,%r9), %eax
   ret
   .cfi_endproc
.LFE11:
   .size  sum, .-sum
   .section   .rodata.str1.1,"aMS",@progbits,1
.LC0:
   .string    "sum is %d!\n"
   .text
   .globl main
   .type  main, @function
main:
.LFB12:
   .cfi_startproc
   subq   $8, %rsp
   .cfi_def_cfa_offset 16
   movl   $6, %r9d
   movl   $5, %r8d
   movl   $4, %ecx
   movl   $3, %edx
   movl   $2, %esi
   movl   $1, %edi
   call   sum
   movl   %eax, %esi
   movl   $.LC0, %edi
   movl   $0, %eax
   call   printf
   movl   $0, %eax
   addq   $8, %rsp
   .cfi_def_cfa_offset 8
   ret
   .cfi_endproc
.LFE12:
   .size  main, .-main
   .ident "GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-44)"
   .section   .note.GNU-stack,"",@progbits
```

# 3 参数大于6个

```c
#include <stdio.h>

int sum(int a1,int a2,int a3,int a4,int a5,int a6,int b1,int b2,int b3){
    return a1+a2+a3+a4+a5+a6+b1+b2+b3;
}

int main() {
    int num = sum(1,2,3,4,5,6,7,8,9);

printf("sum is %d!\n",num);
    return 0;
}
```

```asm
    .file  "parameter2.c"
   .text
   .globl sum
   .type  sum, @function
sum:
.LFB11:
   .cfi_startproc
   addl   %esi, %edi
   addl   %edi, %edx
   addl   %edx, %ecx
   addl   %ecx, %r8d
   addl   %r8d, %r9d
   movl   %r9d, %eax
   addl   8(%rsp), %eax
   addl   16(%rsp), %eax
   addl   24(%rsp), %eax
   ret
   .cfi_endproc
.LFE11:
   .size  sum, .-sum
   .section   .rodata.str1.1,"aMS",@progbits,1
.LC0:
   .string    "sum is %d!\n"
   .text
   .globl main
   .type  main, @function
main:
.LFB12:
   .cfi_startproc
   subq   $40, %rsp
   .cfi_def_cfa_offset 48
   movl   $9, 16(%rsp)
   movl   $8, 8(%rsp)
   movl   $7, (%rsp)
   movl   $6, %r9d
   movl   $5, %r8d
   movl   $4, %ecx
   movl   $3, %edx
   movl   $2, %esi
   movl   $1, %edi
   call   sum
   movl   %eax, %esi
   movl   $.LC0, %edi
   movl   $0, %eax
   call   printf
   movl   $0, %eax
   addq   $40, %rsp
   .cfi_def_cfa_offset 8
   ret
   .cfi_endproc
.LFE12:
   .size  main, .-main
   .ident "GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-44)"
   .section   .note.GNU-stack,"",@progbits
```

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