[all-commits] [llvm/llvm-project] 3ff9ab: [LFI][AArch64] Do not flush deferred LR guards on ...

[Sharjeel Khan via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3ff9abe8930acc7b4c4e2387c1357ca6f2d15c00
      https://github.com/llvm/llvm-project/commit/3ff9abe8930acc7b4c4e2387c1357ca6f2d15c00
  Author: Sharjeel Khan <sharjeelkhan at google.com>
  Date:   2026-09-18 (Fri, 18 Sep 2026)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
    M llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCLFIRewriter.cpp
    M llvm/test/MC/AArch64/LFI/guard-elim.s
    M llvm/test/MC/AArch64/LFI/return.s

  Log Message:
  -----------
  [LFI][AArch64] Do not flush deferred LR guards on temporary labels (#224776)

In function epilogues with unwinding enabled, DWARF CFI directives
between restoring x30 and autiasp trigger
MCObjectStreamer::emitCFILabel, which emits temporary labels. onLabel
assumed all labels were branch targets and flushed DeferredLRGuard,
emitting `add x30, x27, w30, uxtw` before autiasp. Because w30
zero-extends, this stripped the PAC signature from x30 and caused PAC
exceptions on hardware with FEAT_FPAC.

Fix it by not flushing the deferred LR guard on temporary symbols in
onLabel. Also, update AArch64InstrInfo::getLFIInstSizeInBytes to return
8 for RET to fix the size assertion failure in +assertions builds, which
occurs because RET did not account for the deferred LR guard that can
precede the return instruction.

Assisted-by: Gemini



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