[clang] [clang][CodeGen] Fix stack-use-after-return in deferred annotations (PR #226942)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Philipp Dominik Schubert (pdschbrt)

<details>
<summary>Changes</summary>

CodeGenModule::DeferredAnnotations was keyed by StringRef, but not every mangled name passed to GetOrCreateLLVMFunction outlives the call. CodeGenVTables::maybeEmitThunk mangles the thunk name into a stack-local SmallString and hands it to GetAddrOfThunk, so for an annotated virtual function the map retained a reference into a frame that was gone by the time EmitGlobalAnnotations looked the key up.

ASan reports this as a stack-use-after-return in EmitGlobalAnnotations, with the freed frame being maybeEmitThunk's 'Name'. The user-visible effect is that annotations silently disappear from the this-adjusting thunks once the dead frame has been reused.

Make the key own its storage, using StringMap<unsigned> as the MapVector map type so lookups still hash a StringRef without allocating.

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Full diff: https://github.com/llvm/llvm-project/pull/226942.diff


4 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+4) 
- (modified) clang/lib/CodeGen/CodeGenModule.cpp (+2-2) 
- (modified) clang/lib/CodeGen/CodeGenModule.h (+4-1) 
- (added) clang/test/CodeGenCXX/attr-annotate-thunk.cpp (+40) 


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https://github.com/llvm/llvm-project/pull/226942