[llvm-dev] A stage2 build causes changes to libllvm impacting program using it (exemple: rustc)

[Philip Pfaffe via llvm-dev]

Sorry about the late reply, GMail marked this as spam.

The problem is gcc and clang pass optional arguments differently, so you
can't link e.g. a libllvm built with clang with a libllvm client built with
gcc. The workaround is either using gcc for both, or using a clang where
this is fixed. Here's the PR: https://bugs.llvm.org/show_bug.cgi?id=39427

If I understand correctly, the fix should be going into one of the 7
updates.

Cheers,
Philip

On Sun, Nov 11, 2018 at 8:57 PM Sylvestre Ledru <sylvestre at debian.org>
wrote:

> I don't know yet. Would you have a pointer which explains how to fix the
> issue?
>
> Thanks
> Sylvestre
>
> Le 11/11/2018 à 20:34, Philip Pfaffe a écrit :
> > Hi Sylvestre,
> >
> > isn't this another instance of the clang-7/gcc ABI issue around Optional?
> >
> > llvm::DIBuilder::createFile accepts Optional arguments, and more than
> once people complained to me or on IRC about that particular call
> segfaulting.
> >
> > Cheers,
> > Philip
> >
> > On Sun, Nov 11, 2018 at 9:54 AM Sylvestre Ledru via llvm-dev <
> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> >
> >     Hello,
> >
> >     Lately, I have been working on moving Debian & Ubuntu packages to a
> >     stage2 build.
> >
> >     This means that, instead of shipping llvm-toolchain packages built
> with
> >     gcc, we are rebuilding
> >     everything a second time using the newly built clang.
> >
> >     Now, when pushed to Debian, it caused some unexpected issues in
> >     particular with rust reported here:
> >     https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=913271#35
> >
> >     rustc in Debian was building initially against libllvm built with
> gcc.
> >     It was working fine.
> >     The failure is now happening when the systems saw their libllvm
> upgraded
> >     to the stage2 bootstrap one.
> >
> >     The beginning of the backtrace is the following (generating debug
> info):
> >
> >     Thread 1 "rustc" received signal SIGSEGV, Segmentation fault.
> >     0x00007ffff1e273bc in
> llvm::StringMapImpl::LookupBucketFor(llvm::StringRef) () from
> /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     (gdb) bt
> >     #0  0x00007ffff1e273bc in
> llvm::StringMapImpl::LookupBucketFor(llvm::StringRef) () from
> /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     #1  0x00007ffff1f654c9 in ?? () from
> /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     #2  0x00007ffff1f65491 in llvm::MDString::get(llvm::LLVMContext&,
> llvm::StringRef) () from /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     #3  0x00007ffff1ee69cd in ?? () from
> /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     #4  0x00007ffff1ee2d12 in
> llvm::DIBuilder::createFile(llvm::StringRef, llvm::StringRef,
> llvm::Optional<llvm::DIFile::ChecksumInfo<llvm::StringRef> >,
> llvm::Optional<llvm::StringRef>) () from
> /usr/lib/x86_64-linux-gnu/libLLVM-7.so.1
> >     #5  0x00007ffff50a01f2 in LLVMRustDIBuilderCreateFile
> (Builder=0x5555555d4180, Filename=0x7ffffffeedd8 "src/main.rs <
> http://main.rs>", Directory=0x555555b3dd10 "$HOME/hello_world")
> >         at /usr/lib/llvm-7/include/llvm/ADT/StringRef.h:85
> >     #6  0x00007ffff501d39e in
> rustc_codegen_llvm::debuginfo::metadata::compile_unit_metadata (tcx=...,
> codegen_unit_name=..., debug_context=0x7ffffffeeeb0) at
> librustc_codegen_llvm/debuginfo/metadata.rs:859 <http://metadata.rs:859>
> >
> >     Disabling the debug generation for rustc fixes the issue (thanks to
> Ximin Luo for the investigation).
> >
> >     Why idea how to workaround this issue ?
> >
> >     Unfortunately, because rustc needs rustc to build itself, I cannot
> check if a simple recompilation fixes it or not.
> >
> >     Cheers,
> >     S
> >
> >
> >     _______________________________________________
> >     LLVM Developers mailing list
> >     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> >     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
>
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