[LLVMdev] Is there a way to verify that debug info metadata are correct ?

[Eli Bendersky]

On Thu, Feb 7, 2013 at 3:12 AM, Sebastien DELDON-GNB
<sebastien.deldon at st.com> wrote:
> Hi all,
>
> I'm using my own front-end that generates LLVM debug info metadata. I was using LLVM 2.9 debug version and I'm moving to LLVM 3.2 debug version of metadata.
> On my example I got llc 3.2 to fail on following assertion:
>
>
> llc: /work1/tools/llvm/3.2/sources/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1471: void llvm::DwarfDebug::endFunction(const llvm::MachineFunction*): Assertion `TheCU && "Unable to find compile unit!"' failed.
> 0  llc             0x0000000000ffb43f
> 1  llc             0x0000000000ffd6ba
> 2  libpthread.so.0 0x00007f5dd70238f0
> 3  libc.so.6       0x00007f5dd6312a75 gsignal + 53
> 4  libc.so.6       0x00007f5dd63165c0 abort + 384
> 5  libc.so.6       0x00007f5dd630b941 __assert_fail + 241
> 6  llc             0x0000000000b22f20 llvm::DwarfDebug::endFunction(llvm::MachineFunction const*) + 3232
> 7  llc             0x0000000000b0ea9b llvm::AsmPrinter::EmitFunctionBody() + 3291
> 8  llc             0x0000000000895f1d
> 9  llc             0x0000000000f995cd llvm::FPPassManager::runOnFunction(llvm::Function&) + 557
> 10 llc             0x0000000000f996b3 llvm::FPPassManager::runOnModule(llvm::Module&) + 51
> 11 llc             0x0000000000f99141 llvm::MPPassManager::runOnModule(llvm::Module&) + 497
> 12 llc             0x0000000000f992bb llvm::PassManagerImpl::run(llvm::Module&) + 171
> 13 llc             0x000000000052feb2 main + 5778
> 14 libc.so.6       0x00007f5dd62fdc4d __libc_start_main + 253
> 15 llc             0x000000000052bc29
> Stack dump:
> 0.      Program arguments: /home/deldon/Work/dev/pgi/linux86/share/llvm/3.2/bin/llc localvar2.ll -march=x86 -o localvar2.s
> 1.      Running pass 'Function Pass Manager' on module 'localvar2.ll'.
> 2.      Running pass 'X86 AT&T-Style Assembly Printer' on function '@foo'
>
>
> To me debug metadata, I'm generating, seem correct, but I can't find why this assert is happening.
> Is there any way to verify that metadata are correct ?
>

I'm not aware of any verifier for the debug metadata (patches welcome
- this would be great to have). However, I'd say you're in good shape
having a clean assertion triggering. All debugging metadata nodes are
linked through "scope" or "context" fields (their parent,
essentially). Something went wrong in the linking in the medatada you
generate. I suppose you're familiar with
http://llvm.org/docs/SourceLevelDebugging.html, though I should point
out that "Reference to context" is what you're looking for in MDNodes.
Synthesize simple C code that is similar to what you're trying to
generate, run it through clang -g and see the MDNodes it creates, and
how these are linked.

Eli