[llvm-branch-commits] [llvm] [BOLT] Fix thread-safety of PointerAuthCFIAnalyzer (PR #165365)

[Gergely Bálint via llvm-branch-commits]

bgergely0 wrote:

There were two options to implement this fix:

1. the one implemented in this PR: guarding the setIgnored calls with a Mutex.

2. add the functions to ignore to a vector (guarded by a mutex), and do all setIgnored calls on a single thread after the parallel part is done.

To make sure option 1 is correct, we have to look for what members of BC are set by setIgnored, and what members are read in the rest of the parallel part of the pass.

### Writes to BC from the setIgnored call
- [BC.UndefinedSymbols](https://github.com/llvm/llvm-project/blob/main/bolt/lib/Core/BinaryFunction.cpp#L3239)
- [BC.SymbolicDisAsm](https://github.com/llvm/llvm-project/blob/main/bolt/lib/Core/BinaryFunction.cpp#L1620-L1621)
- [BC.SymbolToFunctionMap modified from ScanExternalRefs](https://github.com/llvm/llvm-project/blob/main/bolt/lib/Core/BinaryFunction.cpp#L3811)

### What runOnFunction reads from the BC
- the rest of the parallel function only accesses the AArch64MCPlusBuilder through `BC.MIB`, to get bool information about individual instructions, (e.g. `BC.MIB->isPSignOnLR(Inst)`)

---

For this reason I believe it's sufficient to only guard the `setIgnored` calls without creating a vector to hold to-be-ignored functions, and ignore them later on a single thread.

https://github.com/llvm/llvm-project/pull/165365