[llvm-dev] LLC crash while handling DEBUG info

Sun May 31 10:59:51 PDT 2020

I am bit confused - `unit` must be present for definitions, and `optimized `
is also a `definition`, so, `unit` must be present for `optimized ` too. Am
I right?

Mahesha

On Sun, May 31, 2020 at 10:14 PM David Blaikie <dblaikie at gmail.com> wrote:

> definition and optimized are orthogonal (a function could be both, or
> neither) - one says this DISubprogram describes a function definition
> (rather than a declaration) and the other says this function has been
> compiled (so I suppose it must be a definition - though we may not
> rely on/verify that/need that to be true at the moment).
>
> Sounds like you're saying the verifier does check the constraint
> you're interested in (ie: you only hit the assert in
> lib/CodeGen/LexicalScopes if the code is in violation of the
> verifier?) - and the verification check sounds correct/reasonable to
> me. (declarations are owned by the unit - whereas definitions are
> intentionally owned by the llvm::Function and refer to the unit they
> are within so they can be implicitly dropped if the Function is
> dropped - so, yes, the unit must be present for definitions and must
> not be present for non-definitions).
>
> On Sun, May 31, 2020 at 2:53 AM Mahesha S <mahesha.comp at gmail.com> wrote:
> >
> > Hi David
> >
> > If you look at line
> https://github.com/llvm/llvm-project/blob/master/llvm/lib/IR/Verifier.cpp#L1160
> there is IR verification which asserts that only in case of `spFlags =
> DISPFlagDefinition`, the compilation unit (`unit` field) should be present.
> Otherwise, it should *not* be present. In  the crash case, `spFlags =
> DISPFlagOptimized`. So, I guess, `unit` field should *not* be present,
> though I do not know the difference between ` DISPFlagDefinition` and `
> DISPFlagOptimized`.  if that is expected, then we may need to check
> `nullity` of `DISubprogram::getUnit()` before accessing it at
> https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/LexicalScopes.cpp#L53
> >
> > Thanks,
> > Mahesha
> >
> > On Sun, May 31, 2020 at 11:26 AM David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >> 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
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > llvm-dev at lists.llvm.org
> >> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> >
> >
> > --
> > Thanks,
> > Mahesha
>

-- 
Thanks,
Mahesha
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