clangd - Crash updating the AST

[bgemmill]

Clang 19 from the repository at https://apt.llvm.org

$ clang --version
Ubuntu clang version 19.1.0 (++20240903024228+0c641568515a-1~exp1~20240903144250.30)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-19/bin

Crash within clangd analyzing code:

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
 #0 0x000075eb0e08abdf llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec6bdf)
 #1 0x000075eb0e0888e9 llvm::sys::RunSignalHandlers() (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec48e9)
 #2 0x000075eb0e08b330 (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec7330)
 #3 0x000075eb0c321320 (/lib/x86_64-linux-gnu/libc.so.6+0x45320)
 #4 0x000075eb0e022598 llvm::StringMapImpl::LookupBucketFor(llvm::StringRef, unsigned int) (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xe5e598)
 #5 0x000062213975bf26 (/usr/bin/clangd+0x66cf26)
 #6 0x000062213975a408 (/usr/bin/clangd+0x66b408)
 #7 0x0000622139d7ac5f (/usr/bin/clangd+0xc8bc5f)
 #8 0x00006221394db096 (/usr/bin/clangd+0x3ec096)
 #9 0x000062213957d989 (/usr/bin/clangd+0x48e989)
#10 0x0000622139580d7d (/usr/bin/clangd+0x491d7d)
#11 0x0000622139579b90 (/usr/bin/clangd+0x48ab90)
#12 0x00006221395796eb (/usr/bin/clangd+0x48a6eb)
#13 0x00006221396e2841 (/usr/bin/clangd+0x5f3841)
#14 0x000075eb0c378a94 (/lib/x86_64-linux-gnu/libc.so.6+0x9ca94)
#15 0x000075eb0c405c3c (/lib/x86_64-linux-gnu/libc.so.6+0x129c3c)
Signalled during AST worker action: Update

Please let me know what else I should provide

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Ben Gemmill (bgemmill)

Clang 19 from the repository at https://apt.llvm.org ``` $ clang --version Ubuntu clang version 19.1.0 (++20240903024228+0c641568515a-1~exp1~20240903144250.30) Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/lib/llvm-19/bin ```

Crash within clangd analyzing code:

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
 #<!-- -->0 0x000075eb0e08abdf llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec6bdf)
 #<!-- -->1 0x000075eb0e0888e9 llvm::sys::RunSignalHandlers() (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec48e9)
 #<!-- -->2 0x000075eb0e08b330 (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xec7330)
 #<!-- -->3 0x000075eb0c321320 (/lib/x86_64-linux-gnu/libc.so.6+0x45320)
 #<!-- -->4 0x000075eb0e022598 llvm::StringMapImpl::LookupBucketFor(llvm::StringRef, unsigned int) (/usr/lib/llvm-19/bin/../lib/libLLVM.so.19.1+0xe5e598)
 #<!-- -->5 0x000062213975bf26 (/usr/bin/clangd+0x66cf26)
 #<!-- -->6 0x000062213975a408 (/usr/bin/clangd+0x66b408)
 #<!-- -->7 0x0000622139d7ac5f (/usr/bin/clangd+0xc8bc5f)
 #<!-- -->8 0x00006221394db096 (/usr/bin/clangd+0x3ec096)
 #<!-- -->9 0x000062213957d989 (/usr/bin/clangd+0x48e989)
#<!-- -->10 0x0000622139580d7d (/usr/bin/clangd+0x491d7d)
#<!-- -->11 0x0000622139579b90 (/usr/bin/clangd+0x48ab90)
#<!-- -->12 0x00006221395796eb (/usr/bin/clangd+0x48a6eb)
#<!-- -->13 0x00006221396e2841 (/usr/bin/clangd+0x5f3841)
#<!-- -->14 0x000075eb0c378a94 (/lib/x86_64-linux-gnu/libc.so.6+0x9ca94)
#<!-- -->15 0x000075eb0c405c3c (/lib/x86_64-linux-gnu/libc.so.6+0x129c3c)
Signalled during AST worker action: Update

Please let me know what else I should provide

[HighCommander4]

A symbolized stack trace is a good start, see https://clangd.llvm.org/troubleshooting#getting-stacktraces-from-crashes.

If you're able to provide a code example that reproduces the crash, that would be even better.

[bgemmill]

The symbolizer does not appear to be in the llvm apt repo, is there a good way to obtain it for the verison of llvm there?

$ apt show llvm-symbolizer*
N: Unable to locate package llvm-symbolizer*
N: Couldn't find any package by glob 'llvm-symbolizer*'
N: Unable to locate package llvm-symbolizer*
N: Couldn't find any package by glob 'llvm-symbolizer*'
E: No packages found

[HighCommander4]

The symbolizer does not appear to be in the llvm apt repo, is there a good way to obtain it for the verison of llvm there?

The llvm-19 package should provide it.

[vient]

Wonder if llvm-symbolizer will help, binaries in llvm apt repo are stripped. Also note that 20240903024228 is an rc4 version - current version is 20240910033111, and 19.1.0-final packages are not uploaded yet.

[bgemmill]

Ok, the symbolizer is installed:

$ llvm-symbolizer --version
llvm-symbolizer
Ubuntu LLVM version 19.1.0
  Optimized build.

But per @vient crashes still seem to show the binary addresses only.

I'm going to see if I can isolate the file involved.

[bgemmill]

By copying all of the offending headers into a cpp, the crash no longer occurs, but clangd fails to ever complete parsing. This seems to affect programs as simple as int main() { return 0; } with no includes.

The last item in the log that looks interesting is:
ASTWorker building file [path goes here]/clangd-crash.cpp version 2 with command [cmake output location]

But then clangd uses 100% cpu and never finishes. RES looks steady, it looks like it would run forever.

I'm running clangd with --compile-commands-dir=${workspaceFolder}/[cmake output location] --enable-config and cmake has set(CMAKE_EXPORT_COMPILE_COMMANDS 1) to feed it.

edit: workspaceFolder above is set by vscode, which in turn runs clangd.

[HighCommander4]

By copying all of the offending headers into a cpp, the crash no longer occurs, but clangd fails to ever complete parsing. This seems to affect programs as simple as int main() { return 0; } with no includes.

This makes me wonder if the the hang is occurring while indexing standard library headers (clangd has a feature to index these in the background even if you don't include them, so that it can offer auto-complete suggestions even before you included a standard library header).

Can you try with a .clangd file in your workspace root containing:

Index:
  StandardLibrary: No

[bgemmill]

Having this in the workspace root does not seem to have an effect:

Index:
  StandardLibrary: No

While trying to reproduce, I noticed that the clang version in the apt repository changed to ++20240917083724+560ed047d183-1~exp1~20240917083901.36

Is the issue here that 19.1.0 just hasn't been released yet?

[vient]

19.1.0 just hasn't been released yet?

Yes, Debian CI seems to be very slow.

What distro are you on, Ubuntu 24.04? Ubuntu 20.04 still has no 19.1.0-final packages available.

[bgemmill]

It's a docker image from ubuntu 24.04.1:

$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=24.04
DISTRIB_CODENAME=noble
DISTRIB_DESCRIPTION="Ubuntu 24.04.1 LTS"