装配在x86_64 I386 code [英] Assembling i386 code on x86_64

问题描述

预期下code不工作：

The following code does not work as expected:

.intel_syntax noprefix
.arch i386
.data
hello_world:
.ascii "Hello world!\n"
hello_world_end:
.equ hello_world_len, hello_world_end - hello_world
.text
.global _start
_start:
mov ebx, 1
mov ecx, hello_world
mov edx, hello_world_len
mov eax, 4
int 0x80

mov ebx, 0
mov eax, 1
int 0x80

在通过跑：

as test.s -o test.o
ld test.o -o test
./test

它输出什么。当我改变行：

It outputs nothing. When I change the line:

mov ecx, offset hello_world ; added offset

它工作正常。我试图编译原来的code。与 - 32 -march = i386的和 -m elf_i386 链接，但它仍然没有输出

It works fine. I tried compiling the original code with --32 -march=i386 and linking with -m elf_i386 but it still outputs nothing.

$ uname -a
Linux ubuntu 3.2.0-38-generic #60-Ubuntu SMP Wed Feb 13 13:22:43 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

我的猜测是这种情况，因为内存模型不平坦像I386。我能以某种方式效仿呢？

My guess is this happens because the memory model isn't flat like in i386. Can I emulate this somehow?

推荐答案

这不是内存模式。

在气体语法 MOV ECX，参考hello world 用于从内存地址读 参考hello world 如可以通过检查与ndisasm完成拆卸予以确认：

In gas syntax mov ecx, hello_world means a read from memory address hello_world, as can be confirmed by checking the disassembly done with ndisasm:

00000000  BB01000000        mov ebx,0x1
00000005  8B0C25D4104000    mov ecx,[0x4010d4]
0000000C  BA0D000000        mov edx,0xd
00000011  B804000000        mov eax,0x4
00000016  CD80              int 0x80

您需要的是为存储内存地址 参考hello world 的。在气体来完成，该方法是 MOV ECX，偏移参考hello world ，如从拆卸予以确认：

What you want is to store the memory address of hello_world. In gas the way to accomplish that is mov ecx, offset hello_world, as can be confirmed from the disassembly:

00000000  BB01000000        mov ebx,0x1
00000005  B9D4104000        mov ecx,0x4010d4
0000000A  BA0D000000        mov edx,0xd
0000000F  B804000000        mov eax,0x4
00000014  CD80              int 0x80

顺便说一句，另一种方法做的内存地址加载到寄存器的 LEA ECX，参考hello world 。

一些其他的汇编（如NASM和YASM）有不同的语法，这种差异可能会造成混淆，因为可以用一个小桌子来说明：

Some other assemblers (such as NASM and YASM) have different syntax, and this difference may cause confusion, as can be illustrated with a small table:

gas                           NASM/YASM                ndisasm disassembly
mov ecx,hello_world           mov ecx,[hello_world]    mov ecx,[0x4010d4]
mov ecx,[hello_world]         mov ecx,[hello_world]    mov ecx,[0x4010d4]
mov ecx,offset hello_world    mov ecx,hello_world      mov ecx,0x4010d4

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