_start中RET上的nasm分段错误 [英] Nasm segmentation fault on RET in _start

问题描述

section .text
     global _start
_start:
     nop
main:
     mov eax, 1
     mov ebx, 2
     xor eax, eax
     ret

我使用以下命令进行编译:

nasm -f elf main.asm
ld -melf_i386 -o main main.o

运行代码时，Linux抛出分段错误错误

(我正在使用Linux Mint Nadia 64位).为什么会产生此错误?

解决方案

因为> 不是是退出Linux，Windows或Mac上程序的正确方法！ >

_start不是函数，堆栈上没有返回地址，因为没有用户空间调用者可以返回.用户空间中的执行在进程入口点从此处开始(在静态可执行文件中). (或者使用动态链接，它在动态链接器完成后跳到了这里，但是结果相同.)

在Linux/OS X上，堆栈指针指向_start的入口处的argc(有关进程启动环境的更多详细信息，请参阅i386或x86-64 System V ABI文档)；内核在启动用户空间之前将命令行参数args放入用户空间堆栈内存中. (因此，如果您尝试尝试ret，则EIP/RIP = argc =一个小整数，不是有效的地址.如果调试器在地址0x00000001上显示故障，则是这样.)

---

对于Windows，它是ExitProcess，对于Linux，是系统调用- int 80H使用sys_exit(对于x86)或syscall使用60(对于64Bit)或从C库调用exit(如果要链接).

32位Linux

mov     eax, sys_exit ; sys_exit = 1
xor     ebx, ebx
int     80H

64位Linux

mov     rax, 60
xor     rdi, rdi
syscall

Windows

push    0
call    ExitProcess

---

或Windows/Linux链接到C库

call    exit

exit(与原始退出系统调用或libc _exit不同)将首先刷新stdio缓冲区.如果您使用的是_start中的printf，请使用exit确保在退出之前已打印所有输出，即使将stdout重定向到文件(使stdout成为全缓冲而不是行缓冲).

通常建议，如果您使用libc函数，请编写一个main函数并与gcc链接，以便由普通的CRT启动函数调用，您可以ret进行调用.

将main定义为_start的内容并没有什么特别之处，如果它不像_start所调用的C main函数那样，则会混淆使用main标签准备在main返回后退出.

section .text
     global _start
_start:
     nop
main:
     mov eax, 1
     mov ebx, 2
     xor eax, eax
     ret

I compile with these commands:

nasm -f elf main.asm
ld -melf_i386 -o main main.o

When I run the code, Linux throw a segmentation fault error

(I am using Linux Mint Nadia 64 bits). Why this error is produced?

解决方案

Because ret is NOT the proper way to exit a program in Linux, Windows, or Mac!!!!

_start is not a function, there is no return address on the stack because there is no user-space caller to return to. Execution in user-space started here (in a static executable), at the process entry point. (Or with dynamic linking, it jumped here after the dynamic linker finished, but same result).

On Linux / OS X, the stack pointer is pointing at argc on entry to _start (see the i386 or x86-64 System V ABI doc for more details on the process startup environment); the kernel puts command line args into user-space stack memory before starting user-space. (So if you do try to ret, EIP/RIP = argc = a small integer, not a valid address. If your debugger shows a fault at address 0x00000001 or something, that's why.)

---

For Windows it is ExitProcess and Linux is is system call - int 80H using sys_exit, for x86 or using syscall using 60 for 64Bit or a call to exit from the C Library if you are linking to it.

32 bit Linux

mov     eax, sys_exit ; sys_exit = 1
xor     ebx, ebx
int     80H

64 bit Linux

mov     rax, 60
xor     rdi, rdi
syscall

Windows

push    0
call    ExitProcess

---

Or Windows/Linux linking against the C Library

call    exit

exit (unlike a raw exit system call or libc _exit) will flush stdio buffers first. If you used printf from _start, use exit to make sure all output is printed before you exit, even if stdout is redirected to a file (making stdout full-buffered, not line-buffered).

It's generally recommended that if you use libc functions, you write a main function and link with gcc so it's called by the normal CRT start functions which you can ret to.

Defining main as something that _start falls through into doesn't make it special, it's just confusing to use a main label if it's not like a C main function called by a _start that's prepared to exit after main returns.

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