编译错误 "impossible constraint in 'asm'"

Question

我试图在我的 "SunOS sun4v 5.10" 系统上编译 Csmith，但出现如下错误：

platform.cpp: In function 'long unsigned int platform_gen_seed()':
platform.cpp:78: error: impossible constraint in 'asm'

谁能告诉我错在哪里？

#if (TARGET_CPU_powerpc == 1 || TARGET_CPU_powerpc64 == 1)
/*For PPC, got from:
http://lists.ozlabs.org/pipermail/linuxppc-dev/1999-October/003889.html
*/
static unsigned long long read_time(void) {
    unsigned long long retval;
    unsigned long junk;
    __asm__ __volatile__ ("\n\
1:  mftbu %1\n\
    mftb %L0\n\
    mftbu %0\n\
    cmpw %0,%1\n\
    bne 1b"
    : "=r" (retval), "=r" (junk));
    return retval;
}
#else
#ifdef WIN32
static unsigned __int64 read_time(void) {
        unsigned l, h;
        _asm {rdtsc    
        mov l, eax  
        mov h, edx 
        }
        return (h << 32) + l ;
}
#else
static long long read_time(void) {
        long long l;
        asm volatile(   "rdtsc\n\t"
                : "=A" (l)
        );
        return l;
}
#endif
#endif

unsigned long platform_gen_seed()
{
    return (long) read_time();
}

Answer 1

问题是您尝试编译的代码假设任何不是 PowerPC 的目标 CPU 必须是 x86 处理器。该代码根本不支持您的 SPARC CPU.

幸运的是，这段代码似乎并不重要，它显然只是用来为随机数生成器提供种子，然后用它来创建随机 C 程序。目标是防止同时启动的程序的多个实例生成相同的随机程序。我会用不依赖于 CPU 的更便携的代码替换代码。像这样：

#ifdef WIN32

unsigned long platform_gen_seed()
{
    LARGE_INTEGER now;
    QueryPerformanceCounter(&now);
    return now.LowPart;
}

#else /* assume something Unix-like */

static unsigned long generic_gen_seed() {
    pid_t pid = getpid();
    time_t now;
    time(&now);
    return (unsigned long)(now ^ (pid << 16 | ((pid >> 16) & 0xFFFF)));
}

#ifdef CLOCK_REALTIME

unsigned long platform_gen_seed()
{
    struct timespec now, resolution;
    if (clock_gettime(CLOCK_REALTIME, &now) == -1
        || clock_getres(CLOCK_REALTIME, &resolution) == -1
            || resolution.tv_sec > 0 || resolution.tv_nsec > 1000000) {
        return generic_gen_seed();
    }
    return (now.tv_nsec / resolution.tv_nsec
        + now.tv_sec * resolution.tv_nsec);
}

#else 

unsigned long platform_gen_seed()
{
    return generic_gen_seed();
}

#endif /* CLOCK_REALTIME */

#endif /* WIN32 */

代码已在 Linux 和 Windows 上单独测试。它也应该在 Solaris SPARC 上独立工作，但我不知道它在实际程序的上下文中工作得如何。

编译错误 "impossible constraint in 'asm'"

compiling error "impossible constraint in 'asm'"

assembly

gcc

solaris

inline-assembly