x86-64传参规则

1. 一个参数用rdi（edi）传
2. 两个参数用rdi、rsi（edi、rsi）传
3. 三个参数用rdi、rsi、rdx（edi、esi、edx）传
4. 四个参数用rdi、rsi、rdx、rcx（edi、esi、edx、ecx）传
5. 五个参数用rdi、rsi、rdx、rcx、r8（edi、esi、edx、ecx、r8）传
6. 六个参数用rdi、rsi、rdx、rcx、r8、r9（edi、esi、edx、ecx、r8、r9）传

这里用gcc编了一个小程序用来验证传参规则

source

---

#include<stdio.h>
void fun1(int a)
{}
void fun2(int a,int b)
{}
void fun3(int a,int b,int c)
{}
void fun4(int a,int b,int c,int d)
{}
void fun5(int a,int b,int c,int d,int e)
{}
void fun6(int a,int b,int c,int d,int e,int f)
{}
void main()
{
	int a,b,c,d,e,f;
	a=b=c=d=e=f=2;
	fun1(a);
	fun2(a,b);
	fun3(a,b,c);
	fun4(a,b,c,d);
	fun5(a,b,c,d,e);
	fun6(a,b,c,d,e,f);
}

disassemble

---

   0x0000555555554696 <+48>:	mov    edi,eax
   0x0000555555554698 <+50>:	call   0x5555555545fa <fun1>//一个参数用edi(rdi)传
   0x000055555555469d <+55>:	mov    edx,DWORD PTR [rbp-0x8]
   0x00005555555546a0 <+58>:	mov    eax,DWORD PTR [rbp-0x4]
   0x00005555555546a3 <+61>:	mov    esi,edx
   0x00005555555546a5 <+63>:	mov    edi,eax
   0x00005555555546a7 <+65>:	call   0x555555554604 <fun2>//两个参数用edi、rsi（rdi、rsi）传
   0x00005555555546ac <+70>:	mov    edx,DWORD PTR [rbp-0xc]
   0x00005555555546af <+73>:	mov    ecx,DWORD PTR [rbp-0x8]
   0x00005555555546b2 <+76>:	mov    eax,DWORD PTR [rbp-0x4]
   0x00005555555546b5 <+79>:	mov    esi,ecx
   0x00005555555546b7 <+81>:	mov    edi,eax
   0x00005555555546b9 <+83>:	call   0x555555554611 <fun3>//三个参数用edi、esi、edx（rdi、rsi、rdx）传
   0x00005555555546be <+88>:	mov    ecx,DWORD PTR [rbp-0x10]
   0x00005555555546c1 <+91>:	mov    edx,DWORD PTR [rbp-0xc]
   0x00005555555546c4 <+94>:	mov    esi,DWORD PTR [rbp-0x8]
   0x00005555555546c7 <+97>:	mov    eax,DWORD PTR [rbp-0x4]
   0x00005555555546ca <+100>:	mov    edi,eax
   0x00005555555546cc <+102>:	call   0x555555554621 <fun4>//四个参数用edi、esi、edx、ecx（rdi、rsi、rdx、rcx）传
   0x00005555555546d1 <+107>:	mov    edi,DWORD PTR [rbp-0x14]
   0x00005555555546d4 <+110>:	mov    ecx,DWORD PTR [rbp-0x10]
   0x00005555555546d7 <+113>:	mov    edx,DWORD PTR [rbp-0xc]
   0x00005555555546da <+116>:	mov    esi,DWORD PTR [rbp-0x8]
   0x00005555555546dd <+119>:	mov    eax,DWORD PTR [rbp-0x4]
   0x00005555555546e0 <+122>:	mov    r8d,edi
   0x00005555555546e3 <+125>:	mov    edi,eax
   0x00005555555546e5 <+127>:	call   0x555555554634 <fun5>//五个参数用edi、esi、edx、ecx、r8（rdi、rsi、rdx、rcx、r8）传
   0x00005555555546ea <+132>:	mov    r8d,DWORD PTR [rbp-0x18]
   0x00005555555546ee <+136>:	mov    edi,DWORD PTR [rbp-0x14]
   0x00005555555546f1 <+139>:	mov    ecx,DWORD PTR [rbp-0x10]
   0x00005555555546f4 <+142>:	mov    edx,DWORD PTR [rbp-0xc]
   0x00005555555546f7 <+145>:	mov    esi,DWORD PTR [rbp-0x8]
   0x00005555555546fa <+148>:	mov    eax,DWORD PTR [rbp-0x4]
   0x00005555555546fd <+151>:	mov    r9d,r8d
   0x0000555555554700 <+154>:	mov    r8d,edi
   0x0000555555554703 <+157>:	mov    edi,eax
   0x0000555555554705 <+159>:	call   0x55555555464b <fun6>//六个参数用edi、esi、edx、ecx、r8、r9（rdi、rsi、rdx、rcx、r8、r9）传