x86 linux系统调用的调用约定? [英] x86 linux system call calling convention?

问题描述

给出此代码:

section     .text
global      _start                              
_start:                                         ;tell linker entry point
    mov     edx,len                            ;message length
    mov     ecx,msg                             ;message to write
    mov     ebx,1                               ;file descriptor (stdout)
##  mov     eax,4                               ;system call number (sys_write)
    int     0x80                                ;call kernel
    mov     eax,1                               ;system call number (sys_exit)
    int     0x80                                ;call kernel

section     .data

msg     db  'Hello, world!',0xa                 ;our dear string
len     equ $ - msg                         ;length of our dear string

内核如何知道 msg 在 ecx 中，在 len 在 edx 中，等等?我们不向内核"传递参数?

How does the kernel know that msg is in ecx, len in edx, etc? We do not pass arguments to "kernel"?

推荐答案

这就是您传递参数的方式.系统调用的调用约定说明哪些寄存器保存参数.内核希望它们在那里，您应该将它们放在那里.另请参见此参考.

That is how you pass the arguments. The calling convention for system calls says which registers hold the arguments. The kernel expects them there, and you should put them there. See also this reference.

虽然通常的32位 cdecl 约定使用堆栈来传递参数，但在用户模式下也存在类似的约定(特别是 fastcall )，它们也使用寄存器来传递参数.x86-64的标准约定也可以做到这一点.

While the usual 32 bit cdecl convention uses the stack to pass arguments, there are similar conventions in user mode (notably fastcall) that also use registers to pass arguments. The standard conventions for x86-64 do that as well.

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