多行内联汇编宏与字符串 [英] Multi line inline assembly macro with strings

问题描述

我正在尝试实现一个宏（ MY_MACRO ），该宏在某个部分（ my_section）。
示例： MY_MACRO（200，我的第一个字符串％u％x）;

I'm trying to implement a macro ("MY_MACRO"), which stores a string preceded by a 32 bit integer number in a certain section ("my_section"). Example: MY_MACRO(200, "my first string %u %x");

此处是我尝试过的选择以及面临的问题。我将不胜感激任何帮助。
（）

Here are the options I tried and the problems I'm facing with. I would appreciate any help. (gcc 4.7.3. MIPS cpu)

#define MY_MACRO(_num, _string)\
asm volatile(".pushsection .my_section");\
asm volatile(".byte %0, %1, %2, %3" : : "i"((_num >> 24) & 0xFF), "i"((_num >> 16) & 0xFF), "i"((_num >> 8) & 0xFF), "i"(_num & 0xFF)); /* Store the number */ \
asm volatile(".ascii " #_string);\
asm volatile(".popsection");

编译错误（并非每次使用宏都会发生）：

Compile error (it doesn't occur for each usage of the macro):

c:\Temp\ccpDEDnt.s: Assembler messages:
c:\Temp\ccpDEDnt.s:1024: Warning: .popsection without corresponding .pushsection; ignored

我认为原因是编译器优化会更改指令顺序（尽管每个asm指令都是易变的，则允许编译器更改顺序）。
问：是否可以在没有 #pragma 的情况下仅针对这些行的范围禁用编译器优化？
这个问题使我找到了将四个asm指令统一的解决方案。

I think the reason is a compiler optimization which changes the instructions order (although each asm instruction is volatile, the compiler is allowed to change the order). Q: Is there any way to disable the compiler optimizations just for the scope of these lines without #pragma? This issue led me to find a solution in which the four asm instructions are unified.

#define MY_MACRO(_num, _string)\
asm volatile(".pushsection .my_section\n\t" \
             ".byte %0, %1, %2, %3\n\t" \
             ".ascii " #_string "\n\t" \
             ".popsection" \
             : : "i"((_num >> 24) & 0xFF), "i"((_num >> 16) & 0xFF), "i"((_num >> 8) & 0xFF), "i"(_num & 0xFF));

编译器错误：

foo.c:733:13: error: invalid 'asm': operand number missing after %-letter
foo.c:733:13: error: invalid 'asm': operand number out of range

由于字符串包含百分号（％），因此编译器将其解释为asm操作数。

Since the string includes the percent sign (%), the compiler interprets it as an asm operands.

#define MY_MACRO(_num, _string)\
asm volatile(".pushsection .my_section\n\t" \
             ".byte %0, %1, %2, %3\n\t" \
             ".ascii %4\n\t" \
             ".popsection" \
             : : "i"((_num >> 24) & 0xFF), "i"((_num >> 16) & 0xFF), "i"((_num >> 8) & 0xFF), "i"(_num & 0xFF), "X"(#_string));

在这里，我尝试将字符串作为操作数传递。我什至不知道这是否可行。
我没有设法编译这段代码。

Here I tried to pass the string as an operand. I don't even know if it's feasible. I didn't manage to compile this code.

推荐答案

选项B 是正确的方法，但是您需要将字符串中出现的所有百分号（％）加倍，因为这被解释为嵌入式asm中的操作数占位符。

Option B is the right way, however you will need to double all percent signs (%) occurring in your string because that's interpreted as an operand placeholder in the inline asm.

如果您不特别在意订购或内联，也可以让 gcc 为您处理：

If you don't particularly care about ordering or inlining, you could also let gcc handle it for you:

struct mystruct
{
    int num;
    char string[0];
};

#define MY_MACRO(_num, _string)\
{ static struct mystruct entry __attribute__ ((section (".my_section"))) = { _num, _string }; }

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