括号中的 g++ 内联汇编不匹配 [英] g++ inline assembly mismatch in brackets

问题描述

g++ 向我抱怨以下代码中缺少括号:

g++ is complaining to me about a missing bracket in the following code:

                                              1                   2 3
                                              v                   v v
__asm__ volatile("inb %1, %0" : : "=a" (result) : "Nd" (portnumber) );
                ^                      ^               ^
                1                      2               3

如您所见，括号是匹配的，并且有三个左括号和三个右括号.

as you can see the brackets are matching and there are three open brackets and three close brackets.

还有更多信息，我正在关注 youtube 教程

also for more information i am following a youtube tutorial

推荐答案

您在输出之前有一个额外的 :，因此您最终在输出声明中输入部分.该错误的原因是:您的输入操作数声明，其中编译器需要 clobber 列表. clobber 列表只能包含字符串文字(寄存器名称和 memory" 和/或 cc"¹)，而不是 ().

You have an extra : before the output, so you ended up with your output declaration in the input part. And the reason for that error: your input operand declaration where the compiler expects the clobber list. The clobber list can only include string literals (register names and "memory" and/or "cc"¹), not ().

    __asm__ volatile("inb %1, %0" 
            : "=a" (result)       // output
            : "Nd" (portnumber)   // input
          //  : "memory"   // optional, clobber list
     );

您可能需要一个 "memory" 破坏者列表来确保这是有序的.内存访问.或者不，如果你确定它不需要.

You might want a "memory" clobber list to make sure this is ordered wrt. memory accesses. Or not, if you're sure it doesn't need to be.

脚注 1:x86 上的 asm 语句隐含地破坏了条件代码，cc".如果您愿意，可以将其用于文档.但是你不希望它在这里，因为 inb 不接触 EFLAGS.

Footnote 1: asm statements on x86 implicitly clobber the condition codes, "cc". You can use it for documentation if you like. But you don't want it here because inb doesn't touch EFLAGS.

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