基本组件在 Mac (x86_64+Lion) 上不起作用? [英] basic assembly not working on Mac (x86_64+Lion)?

问题描述

这是代码(exit.s):

here is the code(exit.s):

.section .data,
.section .text,
.globl _start
_start:
    movl $1, %eax
    movl $32, %ebx
    syscall

当我执行 " 作为 exit.s -o exit.o && ld exit.o -o exit -e _start && ./exit"

返回的是Bus error: 10"，而echo $?"的输出是138

the return is "Bus error: 10" and the output of "echo $?" is 138

我也试过这个问题中正确答案的例子:处理命令Linux 64 位行

I also tried the example of the correct answer in this question: Process command line in Linux 64 bit

仍然得到总线错误"...

stil get "bus error"...

推荐答案

首先，您在 Mac OS X 上使用旧的 32 位 Linux 内核调用约定 - 这绝对行不通.

First, you are using old 32-bit Linux kernel calling convention on Mac OS X - this absolutely doesn't work.

其次，Mac OS X 中的系统调用以不同的方式构建——它们都有一个前导类标识符和一个系统调用号.该类可以是 Mach、BSD 或其他东西(参见 此处 在 XNU 源代码中)并向左移动 24 位.正常的 BSD 系统调用具有 2 类，因此从 0x2000000 开始.0 类中的系统调用无效.

Second, syscalls in Mac OS X are structured in a different way - they all have a leading class identifier and a syscall number. The class can be Mach, BSD or something else (see here in the XNU source) and is shifted 24 bits to the left. Normal BSD syscalls have class 2 and thus begin from 0x2000000. Syscalls in class 0 are invalid.

根据 SysV AMD64 ABI 的 §A.2.1，也遵循在 Mac OS X 中，系统调用 ID(连同它在 XNU 上的类！)转到 %rax(或 %eax，因为 XNU 上未使用高 32 位).第一个参数在 %rdi 中.接下来转到 %rsi.等等.%rcx 被内核使用并且它的值被破坏，这就是为什么 libc.dyld 中的所有函数在进行系统调用之前将其保存到 %r10(类似于 syscall_sw.h 中的 kernel_trap 宏).

As per §A.2.1 of the SysV AMD64 ABI, also followed by Mac OS X, syscall id (together with its class on XNU!) goes to %rax (or to %eax as the high 32 bits are unused on XNU). The fist argument goes in %rdi. Next goes to %rsi. And so on. %rcx is used by the kernel and its value is destroyed and that's why all functions in libc.dyld save it into %r10 before making syscalls (similarly to the kernel_trap macro from syscall_sw.h).

第三，Mach-O 二进制文件中的代码部分称为 __text 而不是 Linux ELF 中的 .text 并且也驻留在 __TEXT 中段，统称为 (__TEXT,__text)(如果选择 Mach-O 作为目标对象类型，nasm 会自动适当地翻译 .text)- 请参阅 Mac OS X ABI Mach-O文件格式参考.即使您得到正确的汇编指令，将它们放在错误的段/节中也会导致总线错误.您可以使用 .section __TEXT,__text 指令(请参阅 here 用于指令语法)或者您也可以使用(更简单的).text 指令，或者您可以完全删除它，因为它是如果没有向 as 提供 -n 选项(请参阅 as 的联机帮助页)，则假定.

Third, code sections in Mach-O binaries are called __text and not .text as in Linux ELF and also reside in the __TEXT segment, collectively referred as (__TEXT,__text) (nasm automatically translates .text as appropriate if Mach-O is selected as target object type) - see the Mac OS X ABI Mach-O File Format Reference. Even if you get the assembly instructions right, putting them in the wrong segment/section leads to bus error. You can either use the .section __TEXT,__text directive (see here for directive syntax) or you can also use the (simpler) .text directive, or you can drop it altogether since it is assumed if no -n option was supplied to as (see the manpage of as).

第四，Mach-O ld 的默认入口点称为 start(虽然，正如您已经知道的，它可以通过-e 链接器选项).

Fourth, the default entry point for the Mach-O ld is called start (although, as you've already figured it out, it can be changed via the -e linker option).

鉴于上述所有内容，您应该修改汇编源代码如下:

Given all the above you should modify your assembler source to read as follows:

; You could also add one of the following directives for completeness
; .text
; or
; .section __TEXT,__text

.globl start
start:
    movl $0x2000001, %eax
    movl $32, %edi
    syscall

就是这样，按预期工作:

Here it is, working as expected:

$ as -o exit.o exit.s; ld -o exit exit.o
$ ./exit; echo $?
32

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