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

[Eric Christopher via llvm-commits]

Let's go ahead and revert in the meantime, can totally reapply later.

On Wed, Aug 24, 2022, 5:37 PM Matthias Braun via Phabricator <
reviews at reviews.llvm.org> wrote:

> 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
>
> CHANGES SINCE LAST ACTION
>   https://reviews.llvm.org/D131270/new/
>
> https://reviews.llvm.org/D131270
>
>
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