[llvm-dev] LLC crash while handling DEBUG info

Sat May 30 22:56:13 PDT 2020

In theory the LLVM IR verifier (llvm/lib/IR/Verifier.cpp) should catch
this sort of thing. Maybe it isn't running in llc? It probably should
be. It's also likely not exhaustive to completely arbitrary changes to
the debug info IR - but could be improved if there are particular
things folks come across/want to sure it up against.

On Sat, May 30, 2020 at 10:27 PM Mahesha S via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hi-
>
> Here is the simple C++ function:
>
> -----------
> void foo() {
> }
> -----------
>
> Let's say, above function is compiled to generate LLVM IR with -g flag
> using the command line `clang++ -g -O0 -S -emit-llvm foo.cpp`, we get
> below IR
>
> -----------
> ; ModuleID = 'foo.cpp'
> source_filename = "foo.cpp"
> target datalayout =
> "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-unknown-linux-gnu"
>
> ; Function Attrs: noinline nounwind optnone uwtable
> define dso_local void @_Z3foov() #0 !dbg !7 {
>   ret void, !dbg !10
> }
>
> attributes #0 = { noinline nounwind optnone uwtable
> "correctly-rounded-divide-sqrt-fp-math"="false"
> "disable-tail-calls"="false" "frame-pointer"="all"
> "less-precise-fpmad"="false" "min-legal-vector-width"="0"
> "no-infs-fp-math"="false" "no-jump-tables"="false"
> "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
> "no-trapping-math"="false" "stack-protector-buffer-size"="8"
> "target-cpu"="x86-64"
> "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
> "unsafe-fp-math"="false" "use-soft-float"="false" }
>
> !llvm.dbg.cu = !{!0}
> !llvm.module.flags = !{!3, !4, !5}
> !llvm.ident = !{!6}
>
> !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file:
> !1, producer: "clang version 11.0.0
> (https://github.com/llvm/llvm-project
> 9e0b52e2e68412a9a2add18697f4246e5e5ee5e3)", isOptimized: false,
> runtimeVersion: 0, emissionKind: FullDebug, enums: !2,
> splitDebugInlining: false, nameTableKind: None)
> !1 = !DIFile(filename: "foo.cpp", directory:
> "/home/mahesha/ROCm/issues/hipclang/other/crash/foo")
> !2 = !{}
> !3 = !{i32 7, !"Dwarf Version", i32 4}
> !4 = !{i32 2, !"Debug Info Version", i32 3}
> !5 = !{i32 1, !"wchar_size", i32 4}
> !6 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project
> 9e0b52e2e68412a9a2add18697f4246e5e5ee5e3)"}
> !7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov",
> scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags:
> DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0,
> retainedNodes: !2)
> !8 = !DISubroutineType(types: !9)
> !9 = !{null}
> !10 = !DILocation(line: 2, column: 1, scope: !7)
> -----------
>
> Now, let's say, in the above IR file, I intentionally make debug info
> metadata, a kind of invalid, by removing the field 'unit` and by
> changing the field `spFlags` from `DISPFlagDefinition` to
> `DISPFlagOptimized` within metadata info !7 as shown below.
>
> -----------
> ; ModuleID = 'foo.cpp'
> source_filename = "foo.cpp"
> target datalayout =
> "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-unknown-linux-gnu"
>
> ; Function Attrs: noinline nounwind optnone uwtable
> define dso_local void @_Z3foov() #0 !dbg !7 {
>   ret void
> }
>
> attributes #0 = { noinline nounwind optnone uwtable
> "correctly-rounded-divide-sqrt-fp-math"="false"
> "disable-tail-calls"="false" "frame-pointer"="all"
> "less-precise-fpmad"="false" "min-legal-vector-width"="0"
> "no-infs-fp-math"="false" "no-jump-tables"="false"
> "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
> "no-trapping-math"="false" "stack-protector-buffer-size"="8"
> "target-cpu"="x86-64"
> "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
> "unsafe-fp-math"="false" "use-soft-float"="false" }
>
> !llvm.dbg.cu = !{!0}
> !llvm.module.flags = !{!3, !4, !5}
> !llvm.ident = !{!6}
>
> !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file:
> !1, producer: "clang version 11.0.0
> (https://github.com/llvm/llvm-project
> 9e0b52e2e68412a9a2add18697f4246e5e5ee5e3)", isOptimized: false,
> runtimeVersion: 0, emissionKind: FullDebug, enums: !2,
> splitDebugInlining: false, nameTableKind: None)
> !1 = !DIFile(filename: "foo.cpp", directory:
> "/home/mahesha/ROCm/issues/hipclang/other/crash/foo")
> !2 = !{}
> !3 = !{i32 7, !"Dwarf Version", i32 4}
> !4 = !{i32 2, !"Debug Info Version", i32 3}
> !5 = !{i32 1, !"wchar_size", i32 4}
> !6 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project
> 9e0b52e2e68412a9a2add18697f4246e5e5ee5e3)"}
> !7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov",
> scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags:
> DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
> !8 = !DISubroutineType(types: !9)
> !9 = !{null}
> !10 = !DILocation(line: 2, column: 1, scope: !7)
> -----------
>
> Now, if I compile the above modified IR file using LLC, then LLC
> crashes as below. The crash point is
> https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/LexicalScopes.cpp#L53.
> Reason for crash is `NULL` pointer access. `DISubprogram::getUnit()`
> returns `NULL` pointer since there is no `unit` field in the related
> metadata info.
>
> -----------
> PLEASE submit a bug report to https://bugs.llvm.org/ and include the
> crash backtrace.
> Stack dump:
> 0.      Program arguments: /opt/rocm/llvm/bin/llc foo.ll
> 1.      Running pass 'Function Pass Manager' on module 'foo.ll'.
> 2.      Running pass 'Debug Variable Analysis' on function '@_Z3foov'
>  #0 0x0000556017a2aa8a llvm::sys::PrintStackTrace(llvm::raw_ostream&)
> (/opt/rocm/llvm/bin/llc+0x1883a8a)
>  #1 0x0000556017a28854 llvm::sys::RunSignalHandlers()
> (/opt/rocm/llvm/bin/llc+0x1881854)
>  #2 0x0000556017a289a3 SignalHandler(int) (/opt/rocm/llvm/bin/llc+0x18819a3)
>  #3 0x00007fdb38654890 __restore_rt
> (/lib/x86_64-linux-gnu/libpthread.so.0+0x12890)
>  #4 0x0000556016f013ea
> llvm::LexicalScopes::initialize(llvm::MachineFunction const&)
> (/opt/rocm/llvm/bin/llc+0xd5a3ea)
>  #5 0x0000556016f224dd
> llvm::LiveDebugVariables::runOnMachineFunction(llvm::MachineFunction&)
> (/opt/rocm/llvm/bin/llc+0xd7b4dd)
>  #6 0x0000556016fcb2b0
> llvm::MachineFunctionPass::runOnFunction(llvm::Function&)
> (/opt/rocm/llvm/bin/llc+0xe242b0)
>  #7 0x0000556017375e8f
> llvm::FPPassManager::runOnFunction(llvm::Function&)
> (/opt/rocm/llvm/bin/llc+0x11cee8f)
>  #8 0x0000556017376581 llvm::FPPassManager::runOnModule(llvm::Module&)
> (/opt/rocm/llvm/bin/llc+0x11cf581)
>  #9 0x0000556017376981
> llvm::legacy::PassManagerImpl::run(llvm::Module&)
> (/opt/rocm/llvm/bin/llc+0x11cf981)
> #10 0x000055601662496a main (/opt/rocm/llvm/bin/llc+0x47d96a)
> #11 0x00007fdb372e8b97 __libc_start_main
> /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:344:0
> #12 0x000055601668f2ea _start (/opt/rocm/llvm/bin/llc+0x4e82ea)
> -----------
>
> QUESTION IS:  Is this expected behavior? OR should LLC throw an error
> and abort compilation? OR at the crash point, we are suppose to test
> `nullity` of `DISubprogram::getUnit()` before accessing it?
>
> --
> Thanks,
> Mahesha
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