汇编和系统调用 [英] Assembly and System Calls

问题描述

我在理解组装中更复杂的系统调用时遇到了一些麻烦.我写了一个exec系统调用，效果很好

Im having a bit of trouble understanding the more complex system calls in assembly. I wrote a exec system call and it worked great

 .bss

.text

.globl _start

_start:

#exit(0) system call

        movl $1, %rax
        movl $0, %rbx
        int $0X80

尽管我有一点保证，但无法找到有关如何将字符串放入寄存器的信息.因此，作为一个示例，我想执行一个exec系统调用，因为它的第一个参数需要运行一个文件名，并且我想运行"/bin/bash"，但是如何在rbx中获取它.我什至不知道我必须使用rbx，在X86中我知道我会使用ebx，在amd64 ebx = rbx，ecx = rcs等中是否存在相同的关系?

Though I am a bit insure and have not been able to find info pertaining to how you put strings in a register. So as an example I wanted to do a exec system call and it as its first parameter needs a filename to run and I want to run "/bin/bash", but how do I get that in rbx. How do I even know that I have to use rbx, in X86 I know I would use ebx, is it the same relationship in amd64 ebx=rbx, ecx=rcs, etc.

int execve(const char * filename，char * const argv []， char * const envp []);

int execve(const char *filename, char *const argv[], char *const envp[]);

谢谢

推荐答案

以下是在汇编的这些方面快速取得进展的窍门:让C编译器向您展示它是如何实现的！编写一个可以执行所需操作的C程序，然后键入gcc -S.

Here's a trick to make progress quickly with these aspects of assembly: ask a C compiler to show you how it does it! Write a C program that does what you want to do and type gcc -S.

示例:

Manzana:ppc pascal$ cat t.c
#define NULL ((void*)0)
char *args[] = { "foo", NULL } ;
char *env[] = { "PATH=/bin", NULL } ;


int execve(const char *filename, char *const argv[], char *const envp[]);

int main()
{

  execve("/bin/bash", args, env);

} 

然后:

Manzana:ppc pascal$ gcc -S -fno-PIC t.c  # added no-PIC for readability of generated code
Manzana:ppc pascal$ cat t.s
.globl _args
    .cstring
LC0:
    .ascii "foo\0"
    .data
    .align 2
_args:
    .long   LC0
    .long   0
.globl _env
    .cstring
LC1:
    .ascii "PATH=/bin\0"
    .data
    .align 2
_env:
    .long   LC1
    .long   0
    .cstring
LC2:
    .ascii "/bin/bash\0"
    .text
.globl _main
_main:
    pushl   %ebp
    movl    %esp, %ebp
    subl    $24, %esp
    movl    $_env, 8(%esp)
    movl    $_args, 4(%esp)
    movl    $LC2, (%esp)
    call    _execve
    leave
    ret
    .subsections_via_symbols

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