如何在 GCC C++ 中编写多行内联汇编代码?

问题描述

这看起来不太友好:

__asm("command 1"
      "command 2"
      "command 3");

我真的必须在每一行周围加上双引号吗?

Do I really have to put a doublequote around every line?

另外...由于多行字符串文字在 GCC 中不起作用，我也不能作弊.

Also... since multiline string literals do not work in GCC, I could not cheat with that either.

推荐答案

我总是在 Internet 上找到一些示例，该人手动插入制表符和换行符而不是 和，但是它不适用于我.不太确定您的示例是否可以编译..但我就是这样做的:

I always find some examples on Internet that the guy manually insert a tab and new-line instead of and, however it doesn't work for me. Not very sure if your example even compile.. but this is how I do:

asm volatile(           // note the backslash line-continuation
   "xor %eax,%eax

    mov $0x7c802446, %ebx

    mov $1000, %ax

    push %eax

    call *%ebx

    add $4, %esp

    "
    : "=a"(retval)        // output in EAX: function return value
    :
    : "ecx", "edx", "ebx"   // tell compiler about clobbers
  // Also x87 and XMM regs should be listed.
 );

或者在每一行周围加上双引号，而不是使用 行继续.C 字符串文字仅由空格(包括换行符)单独连接成一个长字符串文字.(这就是为什么你需要 在它里面，所以当它被汇编程序看到时它是单独的行).

Or put double quotes around each line, instead of using line-continuation. C string literals separately only by whitespace (including a newline) are concatenated into one long string literal. (Which is why you need the inside it, so it's separate lines when it's seen by the assembler).

这不那么难看，并且可以在每一行上放置 C 注释.

This is less ugly and makes it possible to put C comments on each line.

asm volatile(
    "xor %eax,%eax
	"
    "mov $0x7c802446, %ebx
	"
    "mov $1000, %ax
	"
    "push %eax
	"  // function arg
    "call *%ebx
	"
    "add $4, %esp
	"  // rebalance the stack: necessary for asm statements
  : "=a"(retval)
  :
  : "ecx", "edx", "ebx"    // clobbers.  Function calls themselves kill EAX,ECX,EDX
  // function calls also clobber all x87 and all XMM registers, omitted here
);

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