如何访问 C 变量以进行内联汇编操作? [英] How to access C variable for inline assembly manipulation?

问题描述

鉴于此代码:

#include <stdio.h>

int main(int argc, char **argv)
{
    int x = 1;
    printf("Hello x = %d
", x);
}

我想在内联汇编中访问和操作变量 x.理想情况下，我想使用内联汇编更改其值.GNU 汇编程序，并使用 AT&T 语法.

I'd like to access and manipulate the variable x in inline assembly. Ideally, I want to change its value using inline assembly. GNU assembler, and using the AT&T syntax.

推荐答案

在 GNU C 内联汇编中，使用 x86 AT&T 语法:
(但是 https://gcc.gnu.org/wiki/DontUseInlineAsm 如果可以避免的话).

In GNU C inline asm, with x86 AT&T syntax:
(But https://gcc.gnu.org/wiki/DontUseInlineAsm if you can avoid it).

// this example doesn't really need volatile: the result is the same every time
asm volatile("movl $0, %[some]"
    : [some] "=r" (x)
);

在此之后，x 包含 0.

after this, x contains 0.

请注意，通常应避免将 mov 作为 asm 语句的第一条或最后一条指令.不要从 %[some] 复制到像 %%eax 这样的硬编码寄存器，只需使用 %[some] 作为寄存器，让编译器进行寄存器分配.

Note that you should generally avoid mov as the first or last instruction of an asm statement. Don't copy from %[some] to a hard-coded register like %%eax, just use %[some] as a register, letting the compiler do register allocation.

参见 https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html 和 https://stackoverflow.com/tags/inline-assembly/info 获取更多文档和指南.

See https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html and https://stackoverflow.com/tags/inline-assembly/info for more docs and guides.

并非所有编译器都支持 GNU 语法.例如，对于 MSVC，您可以这样做:

Not all compilers support GNU syntax. For example, for MSVC you do this:

__asm mov x, 0 和 x 在此语句后将具有 0 的值.

__asm mov x, 0 and x will have the value of 0 after this statement.

请指定您要使用的编译器.

Please specify the compiler you would want to use.

另请注意，这样做会限制您的程序仅使用特定的编译器-汇编器组合进行编译，并且仅针对特定架构.

Also note, doing this will restrict your program to compile with only a specific compiler-assembler combination, and will be targeted only towards a particular architecture.

在大多数情况下，使用纯 C 和内在函数，而不是内联汇编，您将获得同样或更好的结果.

In most cases, you'll get as good or better results from using pure C and intrinsics, not inline asm.

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