[llvm-dev] LLC crash while handling DEBUG info

Mahesha S via llvm-dev
2020-05-31T09:53:20Z

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
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