Valgrind changes CPUID value

Question

Valgrind is changing the values returned by the CPUID opcode instruction. Simply put, how can I make Valgrind respect the actual CPUID instruction?

For reference, this was discovered when running into strange errors when detecting aes-ni support on an old computer which I know does not have the aes-ni instruction set. This behavior, however, is clearly changing multiple values.

This behavior can be observed with valgrind-3.10.1, using the following C code:

#include <stdio.h>

int main() {
        unsigned eax, ebx, ecx, edx;
        eax = 1;
        __asm__ volatile("cpuid"
                : "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx)
                :  "0" (eax),  "2" (ecx)
        );
        if(ecx & (1<<25)) {
                printf("aes-ni enabled (ecx=%08x)n", ecx);
        } else {
                printf("no aes-ni support (ecx=%08x)\n", ecx);
        }
        return 1;
}

Which compiles and runs as such:

$ gcc -o test test.c
$ ./test
no aes-ni support (ecx=0098e3fd)
$ valgrind ./test
==25361== Memcheck, a memory error detector
==25361== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==25361== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==25361== Command: ./test
==25361==
aes-ni enabled (ecx=0298e3ff)
==25361==
==25361== HEAP SUMMARY:
==25361==     in use at exit: 0 bytes in 0 blocks
==25361==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==25361==
==25361== All heap blocks were freed -- no leaks are possible
==25361==
==25361== For counts of detected and suppressed errors, rerun with: -v
==25361== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

请注意，相同的二进制文件通常返回0098e3fd，但在 valgrind 下返回 0298e3ff，这是错误的！

Answer 1

几天后没有得到任何答复，看来 Valgrind 无法允许正确的 CPUID 响应。

因为 Valgrind 本质上是在虚拟环境中运行，所以它将响应有关它所识别的虚拟处理器（而不是系统处理器）的 CPUID 信息。

感谢 @Joe 的评论，以下链接显示了可追溯到 2014 年的有关此问题的对话：https://sourceforge.net/p/valgrind/mailman/message/31960632/

简而言之，如果 Valgrind 能够选择将 CPUID 标志设置为运行时标志（如链接线程中所建议的那样），那就太好了，但迄今为止（2018 年 2 月）尚不存在这样的标志。