LLDB Stuck in llvm::vfs:: Loop

Development LLDB
1

We’re experiencing an issue where LLDB freezes when debugging certain AST contexts. The sampled stack trace suggests that LLDB is stuck in an infinite loop with the following calls involved:

  • llvm::vfs::RedirectingFileSystem::status()
  • llvm::vfs::RedirectingFileSystem::getExternalStatus()
  • clang::FileSystemStatCache::get()
  1. Unfortunately, I don’t have a simple reproducer. The types log doesn’t have information populated, possibly because of the loop.
  2. swift-healthcheck is not an option, as we didn't type any expression.

FB: Feedback Assistant

Questions:

  1. Any recommendations for additional logging or debugging techniques to help diagnose the root cause?
  2. How can we configure a timeout in ~/.lldbInit-Xcode (e.g., some internally decided reasonable threshold X seconds) so that the loop/expr-eval terminates if the timeout is reached?
2

When I enabled all LLDB logs, I came across the following error. After some investigation, I narrowed it down to @objc enums with Int raw values triggering the issue. I have included a reproducer in the FB report.

[LLDBTypeInfoProvider] Could not find clang debug type info for 7SomeLib8ModeTypeO
[LLDBTypeInfoProvider] Could not find clang debug type info for 7SomeLib10ModeTypeV2O
$s7SomeLib10ModeTypeV2OSgD: unimplemented type info in GetEnumCaseName

Additionally, in the reproducer, swift-healthcheck also produces logs indicating the same issue.

[LLDBTypeInfoProvider] Could not find clang debug type info for 7SomeLib10ModeTypeV2O

cc: @Adrian_Prantl