什么是默认的寄存器状态时，程序启动（ASM，LINUX）？ [英] What is default register state when program launches (asm, linux)?

问题描述

在程序启动（Linux中，小精灵） - 有在 EAX ， EBX 零等，或有可以是任何东西（我没有做任何电话或使用的extern libraryies）？在我的机器真是这样，我可以这样写行为ASM programms的时候继电器？

When the program launches (linux, elf) - is there zeros in eax, ebx, etc. or there can be anything (i'm not doing any calls or using extern libraryies)? On my machine it is really so, can I relay on such behavior when writing asm programms?

推荐答案

这在ABI完全取决于每个平台。既然你提到 EAX 和 EBX 让我们来看看有什么针对x86的情况。在 FS / binfmt_elf.c 线＃972，在 load_elf_binary（），内核会检查ABI指定任何< A HREF =htt​​p://lxr.linux.no/#linux+v3.2.4/fs/binfmt_elf.c#L972>要求在程序加载了解寄存器的值：

This depends entirely on the ABI for each platform. Since you mention eax and ebx let's see what's the case for x86. In fs/binfmt_elf.c line #972, inside load_elf_binary(), the kernel checks if the ABI specifies any requirements for register values at program loading:

/*
 * The ABI may specify that certain registers be set up in special
 * ways (on i386 %edx is the address of a DT_FINI function, for
 * example.  In addition, it may also specify (eg, PowerPC64 ELF)
 * that the e_entry field is the address of the function descriptor
 * for the startup routine, rather than the address of the startup
 * routine itself.  This macro performs whatever initialization to
 * the regs structure is required as well as any relocations to the
 * function descriptor entries when executing dynamically links apps.
 */

然后调用 ELF_PLAT_INIT ，这是每个架构中定义的宏弓/ XXX /有/ elf.h中。对于x86，它下面中的：

It then calls ELF_PLAT_INIT, which is a macro defined for each architecture in arch/xxx/include/elf.h. For x86, it does the following:

#define ELF_PLAT_INIT(_r, load_addr)        \
    do {                                    \
        _r->bx = 0; _r->cx = 0; _r->dx = 0; \
        _r->si = 0; _r->di = 0; _r->bp = 0; \
        _r->ax = 0;                         \
    } while (0)

所以，当你的ELF二进制文件被加载在Linux x86，你也不能指望所有的寄存器的值等于零。但这并不意味着你应该，虽然。 ： - ）

So, when your ELF binary is loaded on Linux x86, you could count on all register values being equal to zero. Doesn't mean you should, though. :-)

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