汇编程序模板，asmSymbolicName和＆QUOT;错误：期望的字符串字面＆QUOT;

问题描述

我试图使用GCC的扩展ASM像微软的汇编。根据微软的MASM，我们可以做到以下几点，其中 __ FUNC 是一个C变量：

  MOV EAX，__FUNC
 

根据，第6.44.3.1的输入操作数的：

When I try and use it in code:

unsigned int func = 1;
...

__asm__ __volatile__ (
  "movl %[__FUNC], %%eax"
  ...

  :
  : __FUNC "" (func)
);

It results in:

cpu.cpp:148:5: error: expected string-literal before ‘__FUNC’
 : __FUNC "" (func)
   ^
cpu.cpp:148:5: error: expected ‘(’ before ‘__FUNC’
cpu.cpp:148:17: error: ‘__FUNC’ was not declared in this scope
...

The best I can tell, I am using __FUNC according to the manual and its description of asmSymbolicName. But obviously I am not since there's an error.

What am I doing wrong?

---

I also tried the following because the manual told me I could use variable names in surrounding code, but it did not work either:

"movl %[func], %%eax"
...

:
: func "" (func)

And:

"movl %[func], %%eax"
...

:
: func (func)
...

解决方案

This is correct:

However [asmSymbolicName] means asmSymbolicName is literally surrounded by square brackets [ and ] (The outside brackets say that it is an optional parameter). You might have been going for this:

uint32_t func = 1;
uint32_t result;

__asm__ __volatile__ (
    "movl %[func], %[result]"
    : [result]"=a"(result)
    : [func]"g"(func)
);

This takes an input parameter of func makes it available as a symbolic name called func within the assembler template. Output parameter is eax (writable) with a symbolic name of result and eax will be stored in the C variable result when finished. I chose "g" since any immediate value, memory address, or register would be appropriate for the source in movl . You could pass an immediate value rather than a "C" variable with:

: [func]"g"(42)

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