大会编译错误（gcc4.2.4 =胜利，gcc4.3.3 =失败） [英] Assembly compilation error (gcc4.2.4=win, gcc4.3.3=fail)

问题描述

我们最近从 gcc4.2.4 升级code到 gcc4.3.3 。

We recently upgraded the code to gcc4.3.3 from gcc4.2.4.

void testAndSet(  volatile int*  s, int* val )
{
   __asm__ __volatile__ ( "btsl   $0, %0\n   "
           "jc   bitSet\n   "
           "movl   $0, %1\n   "
           "jmp   returnVector\n"
           "bitSet:\n   "
           "movl   $1, %1\n"
           "returnVector: " : "=m"(*s), "=m"(*val) );
}

我们的code现在失败，出现以下错误，

Our code now fails with the following errors,

lock.cxx: Assembler messages:
lock.cxx:59: Error: symbol `bitSet' is already defined
lock.cxx:61: Error: symbol `returnVector' is already defined
lock.cxx:59: Error: symbol `bitSet' is already defined
lock.cxx:61: Error: symbol `returnVector' is already defined

均未发现这些符号其他地方。 （重命名它们会导致新的名称相同的错误）。

Those symbols weren't found anywhere else. (Renaming them causes the same error with the new name).

这个是怎么回事？为什么会出现错误两次？

What's up with this? why do I get the errors twice?

推荐答案

大概优化已经改变，现在你的内联检查并设置（）函数转换成2位。由于您使用的是全局名称为您的标签，这是行不通的。您应该改用本地名称。例如：

Probably the optimizer has changed and is now inlining your testAndSet() function into 2 places. Because you are using global names for your labels, this does not work. You should use local names instead. E.g:

   __asm__ __volatile__ ( "btsl   $0, %0\n   "
           "jc   0f\n   "
           "movl   $0, %1\n   "
           "jmp   1f\n"
           "0:\n   "
           "movl   $1, %1\n"
           "1: " : "=m"(*s), "=m"(*val) );

局部标签只是数字;为消除歧义，那里有许多标签所谓的0，你需要使用 JMP 0F 向前跳跃和 JMP 0B 为向后跳跃。

Local labels are just numbers; to disambiguate cases where there are many labels called "0" you need to use "jmp 0f" for forward jumps and "jmp 0b" for backward jumps.

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