[PATCH] D131270: MC: make section classification a bit more thorough

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

Hey, I started hitting assertions when creating assembly and subsequently assembling things. In my case I am building the llvm-test-suite with `-save-temps=obj` but I can reproduce with something smaller/simpler:

  struct C {
    C(int x) { a = x; }
    int a;
  };
  inline C& getNullInstance() {
    static C instance(42);
    return instance;
  }
  void* used = (void*)getNullInstance;



  $ CLANG=~/local/llvm-builds/e41dd0205242/bin/clang
  $ $CLANG -S repro.cpp && $CLANG -c repro.s
  # no error
  
  $ CLANG=~/local/llvm-builds/73a9dfcee24d/bin/clang
  $ $CLANG -S repro.cpp && $CLANG -c repro.s
  clang: /tmp/tmpssp98atc/llvm-project/llvm/lib/MC/MCAssembler.cpp:767: void llvm::MCAssembler::writeSectionData(llvm::raw_ostream &, const llvm::MCSection *, const llvm::MCAsmLayout &) const: Assertion `(cast<MCAlignFragment>(F).getValueSize() == 0 || cast<MCAlignFragment>(F).getValue() == 0) && "Invalid align in virtual section!"' failed.
  PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
  Stack dump:
  0.      Program arguments: /home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang -c repro.s
   #0 0x0000000001d15c23 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x1d15c23)
   #1 0x0000000001d13a5e llvm::sys::RunSignalHandlers() (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x1d13a5e)
   #2 0x0000000001d1502d llvm::sys::CleanupOnSignal(unsigned long) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x1d1502d)
   #3 0x0000000001c8a2de (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) CrashRecoveryContext.cpp:0:0
   #4 0x0000000001c8a530 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
   #5 0x00007f919418dce0 __restore_rt (/lib64/libpthread.so.0+0x12ce0)
   #6 0x00007f9192eb0a9f raise (/lib64/libc.so.6+0x4ea9f)
   #7 0x00007f9192e83e05 abort (/lib64/libc.so.6+0x21e05)
   #8 0x00007f9192e83cd9 _nl_load_domain.cold.0 (/lib64/libc.so.6+0x21cd9)
   #9 0x00007f9192ea93f6 (/lib64/libc.so.6+0x473f6)
  #10 0x000000000195b462 llvm::MCAssembler::writeSectionData(llvm::raw_ostream&, llvm::MCSection const*, llvm::MCAsmLayout const&) const (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x195b462)
  #11 0x00000000019e0c0a (anonymous namespace)::ELFWriter::writeObject(llvm::MCAssembler&, llvm::MCAsmLayout const&) ELFObjectWriter.cpp:0:0
  #12 0x00000000019df1f5 (anonymous namespace)::ELFSingleObjectWriter::writeObject(llvm::MCAssembler&, llvm::MCAsmLayout const&) ELFObjectWriter.cpp:0:0
  #13 0x000000000195c4a6 llvm::MCAssembler::Finish() (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x195c4a6)
  #14 0x000000000197ba46 llvm::MCELFStreamer::finishImpl() (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x197ba46)
  #15 0x00000000019e86d1 (anonymous namespace)::AsmParser::Run(bool, bool) AsmParser.cpp:0:0
  #16 0x00000000009e2244 cc1as_main(llvm::ArrayRef<char const*>, char const*, void*) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x9e2244)
  #17 0x00000000009dc4c6 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
  #18 0x0000000002586082 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::$_1>(long) Job.cpp:0:0
  #19 0x0000000001c8a159 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x1c8a159)
  #20 0x0000000002585ad0 clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x2585ad0)
  #21 0x00000000025457e8 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x25457e8)
  #22 0x0000000002545aee clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x2545aee)
  #23 0x00000000025656d0 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x25656d0)
  #24 0x00000000009db8d1 clang_main(int, char**) (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x9db8d1)
  #25 0x00007f9192e9ccf3 __libc_start_main (/lib64/libc.so.6+0x3acf3)
  #26 0x00000000009d8cfe _start (/home/matthiasb/local/llvm-builds/73a9dfcee24d/bin/clang+0x9d8cfe)

Looking at the assembly files with this diff we start emitting `.p2align        2, 0x90` instead of just `.p2align        3` for some weak-symbol things. This subsequently triggers the compiler assertion.

Once I generated the "bad" assembly it hits an assert even in clang/llvm versions before this change...


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D131270/new/

https://reviews.llvm.org/D131270