[llvm-dev] invalid code generated on Windows x86_64 using skylake-specific features

[Andrew Kelley via llvm-dev]

I suspect that there are 2 issues here:

 * I have incorrect alignment somewhere
 * MSVC / .pdb / CodeView debugging is not working correctly.

I think the latter would help solve the former.

I will send out a new email later talking about the issues I'm having
debugging llvm-generated binaries with MSVC.

On Sat, Sep 30, 2017 at 3:33 PM, Andrew Kelley <superjoe30 at gmail.com> wrote:

> I have this code, which works fine on MacOS and Linux hosts:
>
>     const char *target_specific_cpu_args;
>     const char *target_specific_features;
>     if (g->is_native_target) {
>         target_specific_cpu_args = ZigLLVMGetHostCPUName();
>         target_specific_features = ZigLLVMGetNativeFeatures();
>     } else {
>         target_specific_cpu_args = "";
>         target_specific_features = "";
>     }
>
>     g->target_machine = LLVMCreateTargetMachine(target_ref,
> buf_ptr(&g->triple_str),
>             target_specific_cpu_args, target_specific_features, opt_level,
> reloc_mode, LLVMCodeModelDefault);
>
>
>
> char *ZigLLVMGetHostCPUName(void) {
>     std::string str = sys::getHostCPUName();
>     return strdup(str.c_str());
> }
>
> char *ZigLLVMGetNativeFeatures(void) {
>     SubtargetFeatures features;
>
>     StringMap<bool> host_features;
>     if (sys::getHostCPUFeatures(host_features)) {
>         for (auto &F : host_features)
>             features.AddFeature(F.first(), F.second);
>     }
>
>     return strdup(features.getString().c_str());
> }
>
> On this windows laptop that I am testing on, I get these values:
>
> target_specific_cpu_args: skylake
>
> target_specific_features: +sse2,+cx16,-tbm,-avx512ifma,-
> avx512dq,-fma4,+prfchw,+bmi2,+xsavec,+fsgsbase,+popcnt,+aes,
> +xsaves,-avx512er,-avx512vpopcntdq,-clwb,-avx512f,-clzero,-pku,+mmx,-
> lwp,-xop,+rdseed,-sse4a,-avx512bw,+clflushopt,+xsave,-
> avx512vl,-avx512cd,+avx,-rtm,+fma,+bmi,+rdrnd,-mwaitx,+sse4.
> 1,+sse4.2,+avx2,+sse,+lzcnt,+pclmul,-prefetchwt1,+f16c,+
> ssse3,+sgx,+cmov,-avx512vbmi,+movbe,+xsaveopt,-sha,+adx,-avx512pf,+sse3
>
>
> It successfully creates a binary, but the binary when run crashes with:
>
> Unhandled exception at 0x00007FF7C9913BA7 in test.exe: 0xC0000005: Access
> violation reading location 0xFFFFFFFFFFFFFFFF.
>
> The disassembly of the crashed instruction is:
>
> 00007FF7C9913BA7  vmovdqa     xmmword ptr [rbp-20h],xmm0
>
> There is no callstack or source in the MSVC debugger. The .pdb produced is
> 64KB exactly. The file was linked with:
>
> lld -NOLOGO -DEBUG -MACHINE:X64 /SUBSYSTEM:console -OUT:.\test.exe
> -NODEFAULTLIB -ENTRY:_start ./zig-cache/test.obj ./zig-cache/builtin.obj
> ./zig-cache/compiler_rt.obj ./zig-cache/kernel32.lib
>
>
> When I change the call to LLVMCreateTargetMachine so that both
> target_specific_cpu_args  and target_specific_features  are the empty
> string, the produced binary is valid and runs successfully.
>
> Is this an LLVM bug? Am I using the API incorrectly? Is there more
> information I can provide to LLVM-dev mailing list that would make it
> easier to help me?
>
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