问题描述
这是代码(退出):
.section .data,
.section .text,
.globl _start
_start:
movl $1, %eax
movl $32, %ebx
syscall
当我执行" as exit.s -o exit.o && ld exit.o -o exit -e _start && ./exit"
返回的错误是总线错误:10"，输出的"echo $?"是138
the return is "Bus error: 10" and the output of "echo $?" is 138
我也在这个问题中尝试了正确答案的示例: Process命令Linux 64位中的行
I also tried the example of the correct answer in this question: Process command line in Linux 64 bit
stil收到总线错误" ...
stil get "bus error"...
推荐答案
首先，您正在Mac OS X上使用旧的32位Linux内核调用约定-绝对不起作用.
First, you are using old 32-bit Linux kernel calling convention on Mac OS X - this absolutely doesn't work.
第二，Mac OS X中的系统调用以不同的方式构造-它们都具有前导类标识符和.该类可以是Mach，BSD或其他类(请参见此处(在XNU源代码中)，并向左移动24位.普通的BSD系统调用具有类2，因此从0x2000000开始.类0中的系统调用是无效.
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.
还遵循 SysV AMD64 ABI 的§A.2.1.在Mac OS X中，系统调用ID(连同其在XNU上的类！)转到%rax(或由于，因为在XNU上未使用高32位).第一个论点在%rdi中.接下来进入%rsi.等等.内核使用%rcx并破坏其值，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中的原因(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段被称为__text而不是Linux ELF中的.text，并且也位于__TEXT段中，统称为(__TEXT,__text)(nasm自动翻译如果选择了Mach-O作为目标对象类型，则视情况而定)-请参见 Mac OS X ABI Mach-O文件格式参考.即使正确安装了说明，将它们放在错误的段/节中也可能导致总线错误.您可以使用.section __TEXT,__text指令(请参见此处(用于指令语法)，或者您也可以使用(简单的).text指令，或者您可以将其完全删除，因为假设没有为as提供-n选项(请参见as的联机帮助页.
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的默认入口称为start(尽管您已经知道了，可以通过-e链接器选项对其进行更改).
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).
鉴于上述所有情况，您应该将汇编源代码修改为如下内容:
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
在这里，按预期工作:
$ as -o exit.o exit.s; ld -o exit exit.o
$ ./exit; echo $?
32
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