此反斜杠在此汇编代码中起什么作用? [英] What does this backslash do in this assembly code?

问题描述

我不确定这些推送线有什么区别. (从Linux的x86/entry/calling中删除 .h ，清除了零或零"清除.)

I am not sure what the difference is in these push lines. (trimmed down from Linux's x86/entry/calling.h, with the xor-zero clearing removed.)

.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
    pushq \rdx
    pushq \rax
    pushq %r11
    pushq %r12
.endm

是否都推入堆栈?还是前两条推线做些不同的事情?我在Linux上使用GNU工具链.

Do both push onto the stack? Or do the first two push lines do something different? I am on linux using the GNU toolchain.

这些行在.S asm源文件包含的.h文件中找到.

These lines where found in a .h file that's included by .S asm source files.

还有谁能告诉我这段代码的作用吗?

Also can anyone tell me what this code does?

.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0

特别是PUSH_AND_CLEAR_REGS之后的代码.

Specifically the code after PUSH_AND_CLEAR_REGS.

推荐答案

内部 GAS .macro ，则使用\foo引用名为foo的宏参数.

Inside a GAS .macro, you use \foo to refer to a macro parameter called foo.

您正在查看的.macro具有3个带有默认值的参数；大概在某些用例中，他们想要保存替代值来代替RAX和RDX中的实际值.但是其余的寄存器会像平常一样保存并进行异或归零.

The .macro you're looking at has 3 args with default values; presumably in some use-case they want to get alternate values saved in place of what's actually in RAX and RDX. But the rest of the registers get saved and xor-zeroed as normal.

因此，在宏扩展之后，是push %rdx和push %rax，与push %r11和push %r12相同.

So after macro expansion, yes it's just push %rdx and push %rax, same as the push %r11 and push %r12.

IDK(如果您正在查看旧版本的Linux)，但是它在其他.S手写asm源文件中包含的.h中，而.c源中的不是中包含的.我为您解决了问题.

IDK if you were looking at an old version of Linux, but this is in a .h that's included by other .S hand-written asm source files, not by .c sources. I fixed your question for you.

我认为关于GAS宏定义的评论对于此宏的用途非常清楚.请参阅我添加到您的问题的github链接.

I thought the comment on the GAS macro definition was was pretty clear about the purpose of this macro. See the github link I added to your question.

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