Clang 13.0.1 with MSVC-like produces binary that segfaults shortly after __cpuid

[malytomas]

Source code to reproduce:

#include <cstdint>
#include <cstring>
#include <cstdio>

#ifdef _MSC_VER
#include <intrin.h>
#endif

struct cpu_info
{
    cpu_info() { memset(this, 0, sizeof(*this)); }

    bool m_has_fpu;
    bool m_has_mmx;
    bool m_has_sse;
    bool m_has_sse2;
    bool m_has_sse3;
    bool m_has_ssse3;
    bool m_has_sse41;
    bool m_has_sse42;
    bool m_has_avx;
    bool m_has_avx2;
    bool m_has_pclmulqdq;
};

static void extract_x86_flags(cpu_info &info, uint32_t ecx, uint32_t edx)
{
    info.m_has_fpu = (edx & (1 << 0)) != 0;
    info.m_has_mmx = (edx & (1 << 23)) != 0;
    info.m_has_sse = (edx & (1 << 25)) != 0;
    info.m_has_sse2 = (edx & (1 << 26)) != 0;
    info.m_has_sse3 = (ecx & (1 << 0)) != 0;
    info.m_has_ssse3 = (ecx & (1 << 9)) != 0;
    info.m_has_sse41 = (ecx & (1 << 19)) != 0;
    info.m_has_sse42 = (ecx & (1 << 20)) != 0;
    info.m_has_pclmulqdq = (ecx & (1 << 1)) != 0;
    info.m_has_avx = (ecx & (1 << 28)) != 0;
}

static void extract_x86_extended_flags(cpu_info &info, uint32_t ebx)
{
    info.m_has_avx2 = (ebx & (1 << 5)) != 0;
}

#ifndef _MSC_VER
static void do_cpuid(uint32_t eax, uint32_t ecx, uint32_t *regs)
{
    uint32_t ebx = 0, edx = 0;

#if defined(__PIC__) && defined(__i386__)
    __asm__("movl %%ebx, %%edi;"
        "cpuid;"
        "xchgl %%ebx, %%edi;"
        : "=D"(ebx), "+a"(eax), "+c"(ecx), "=d"(edx));
#else
    __asm__("cpuid;" : "+b"(ebx), "+a"(eax), "+c"(ecx), "=d"(edx));
#endif

    regs[0] = eax; regs[1] = ebx; regs[2] = ecx; regs[3] = edx;
}
#endif

static void get_cpuinfo(cpu_info &info)
{
    int regs[4];

#ifdef _MSC_VER
    __cpuid(regs, 0);
#else
    do_cpuid(0, 0, (uint32_t *)regs);
#endif

    const uint32_t max_eax = regs[0];

    if (max_eax >= 1U)
    {
#ifdef _MSC_VER
        __cpuid(regs, 1);
#else
        do_cpuid(1, 0, (uint32_t *)regs);
#endif
        extract_x86_flags(info, regs[2], regs[3]);
    }

    if (max_eax >= 7U)
    {
#ifdef _MSC_VER
        __cpuidex(regs, 7, 0);
#else
        do_cpuid(7, 0, (uint32_t *)regs);
#endif

        extract_x86_extended_flags(info, regs[1]);
    }
}

bool g_cpu_supports_sse41 = false;

void detect_sse41()
{
    cpu_info info;
    get_cpuinfo(info);

    // Check for everything from SSE to SSE 4.1
    g_cpu_supports_sse41 = info.m_has_sse && info.m_has_sse2 && info.m_has_sse3 && info.m_has_ssse3 && info.m_has_sse41;
}

int main()
{
    detect_sse41();
    printf(g_cpu_supports_sse41 ? "supported\n" : "unsupported\n");
    return 0;
}

The issue happens when building the code with RelWithDebInfo cmake configuration only.

The code has been tested with other compilers and configurations in the github actions tests in this repository: https://github.com/malytomas/clang-issue

[EugeneZelenko]

Could you please try main branch?

[malytomas]

Could you please try main branch?

I have only ever used clang-cl that comes together with visual studio installation.

Can you direct me to build instructions specific for the clang-cl, please?

Also how do I use it afterwards. Will this be sufficient: cmake -T ClangCL -DCMAKE_CXX_COMPILER=<the path to the newly build compiler> .. Do I need to build any other components?

Thank you