[cfe-dev] Building latest llvm/clang targeting mingw-64/gcc-6.2 on Windows

[Reid Kleckner via cfe-dev]

I spent some time debugging this, and it's either a GCC miscompile or
instance of UB in tablegen that I can't identify. The 'this' pointer is
corrupted in this call sequence:
    llvm::errs() << "this before EmitProcessorProp: " << (void *)this <<
'\n';
    EmitProcessorProp(OS, PM.ModelDef, "IssueWidth", ',');
    EmitProcessorProp(OS, PM.ModelDef, "MicroOpBufferSize", ',');
    EmitProcessorProp(OS, PM.ModelDef, "LoopMicroOpBufferSize", ',');
    EmitProcessorProp(OS, PM.ModelDef, "LoadLatency", ',');
    EmitProcessorProp(OS, PM.ModelDef, "HighLatency", ',');
    EmitProcessorProp(OS, PM.ModelDef, "MispredictPenalty", ',');
    llvm::errs() << "this after EmitProcessorProp: " << (void *)this <<
'\n';

I suspect a GCC miscompile. The problem goes away when I disable frame
pointer omission, and GCC is doing some interesting IPO transformation,
based on the mangled name of this
function: __ZN12_GLOBAL__N_116SubtargetEmitter17EmitProcessorPropERN4llvm11raw_ostreamEPKNS1_6RecordENS1_9StringRefEc.constprop.549
(note the .constprop)

I think this GCC getting the thiscall calling convention confused. Here's
here it calls EmitProcessorProp:
    7c06: e8 15 97 ff ff       call   1320 <__ZN12_....constprop.549>
    7c0b: 8b 53 1c             mov    0x1c(%ebx),%edx
    7c0e: 83 ec 08             sub    $0x8,%esp

Note the subtraction from ESP. This usually indicates that the callee is
expected to pop 8 bytes off the stack. However, the epilogue of
EmitProcessorProp doesn't do that:
    13c3: 8d 65 f4             lea    -0xc(%ebp),%esp
    13c6: 5b                   pop    %ebx
    13c7: 5e                   pop    %esi
    13c8: 5f                   pop    %edi
    13c9: 5d                   pop    %ebp
    13ca: c3                   ret

Note that it doesn't say "ret $0x8".

Do you want to follow up filing this issue with upstream GCC?

On Fri, Dec 23, 2016 at 7:04 AM, Edward Diener via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> I am building clang from source on Windows using CMake, Ninja, and
> mingw-64/gcc-6.2. I am building in Release mode ( CMAKE_BUILD_TYPE =
> Release ).
>
> When I build with the x64 version of mingw-64/gcc-6.2 with a triple of
> x86_64-w64-mingw32 ( LLVM_DEFAULT_TARGET_TRIPLE = x86_64-w64-mingw32 ),
> everything builds fine and I can produce clang that works properly with a
> 64-bit compilation using the 64-bit version of mingw-64/gcc-6.2.
>
> When I build with the x32 version of mingw-64/gcc-6.2 with a triple of
> i686-pc-mingw32  ( LLVM_DEFAULT_TARGET_TRIPLE = i686-pc-mingw32 ),
> the build fails with:
>
> [8/1856] Building AArch64GenSubtargetInfo.inc...
> FAILED: lib/Target/AArch64/AArch64GenSubtargetInfo.inc.tmp
> cmd.exe /C "cd /D C:\Programming\VersionControl\
> bninja_clang\lib\Target\AArch64
> && C:\Programming\VersionControl\bninja_clang\bin\llvm-tblgen.exe
> -gen-subtarget
> -I E:/Programming/VersionControl/llvm/lib/Target/AArch64 -I
> E:/Programming/VersionControl/llvm/include
> -I E:/Programming/VersionControl/llvm/lib/Target
> E:/Programming/VersionControl/llvm/lib/Target/AArch64/AArch64.td
> -o C:/Programming/VersionControl/bninja_clang/lib/Target/AArch6
> 4/AArch64GenSubtargetInfo.inc.tmp"
> Wrote crash dump file "C:\Users\eldiener\AppData\Loc
> al\Temp\llvm-tblgen.exe-0c060b.dmp"
> 0x004EFB0A (0x0166FA48 0x00000007 0x63724141 0x00343668)
> 0x03172858 (0x77CEE172 0x769B0100 0x00000000 0x00000008) <unknown module>
> 0x77CEE40C (0x001F9A18 0x004F51D0 0x005F40CC 0x00000000),
> RtlInitUnicodeString() + 0x164 bytes(s)
> 0x005CD6B1 (0x0000000B 0x001F99E0 0x001F2B50 0x00000000)
> 0x004013E2 (0x7EFDE000 0x0166FFD4 0x77CF9902 0x7EFDE000)
> 0x768E336A (0x7EFDE000 0x73B4F3DA 0x00000000 0x00000000),
> BaseThreadInitThunk()+ 0x12 bytes(s)
> 0x77CF9902 (0x004014E0 0x7EFDE000 0x00000000 0x00000000),
> RtlInitializeExceptionChain() + 0x63 bytes(s)
> 0x77CF98D5 (0x004014E0 0x7EFDE000 0x00000000 0x00000000),
> RtlInitializeExceptionChain() + 0x36 bytes(s)
> [9/1856] Building AMDGPUGenMCPseudoLowering.inc...
> ninja: build stopped: subcommand failed.
>
> I notice that AArch64 is listed as a target type even when building with a
> 32-bit compiler and am guessing that this is what is causing the build to
> fail.
>
> Is this an LLVM problem or a clang problem ?
>
> How can I get someone to correct this in the CMake files in the LLVM/clang
> project ?
>
> Is there some way I myself can tell CMake to not build for the AArch64
> target ?
>
>
> _______________________________________________
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> cfe-dev at lists.llvm.org
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>
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