Date: Tue, 28 Jul 2026 11:54:35 +0000 From: Jessica Clarke <jrtc27@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 70509d1d9cba - main - Merge commit 6b0a46958c56 from llvm-project (by Piotr Kubaj): Message-ID: <6a68987b.32f8e.3d475221@gitrepo.freebsd.org>
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The branch main has been updated by jrtc27: URL: https://cgit.FreeBSD.org/src/commit/?id=70509d1d9cba254dfd5b3dd83d8a011b5e125788 commit 70509d1d9cba254dfd5b3dd83d8a011b5e125788 Author: Jessica Clarke <jrtc27@FreeBSD.org> AuthorDate: 2026-07-28 11:54:04 +0000 Commit: Jessica Clarke <jrtc27@FreeBSD.org> CommitDate: 2026-07-28 11:54:04 +0000 Merge commit 6b0a46958c56 from llvm-project (by Piotr Kubaj): [libunwind][PPC64] Fix unw_getcontext corrupting callee-saved VSX registers on LE (#198371) This is the first of two independent fixes for libunwind on ppc64le (ELFv2 ABI, little-endian), where two separate bugs together cause SIGSEGV during backtracing. This commit addresses the VSX register corruption; the TOC-restore fault is handled in a follow-up. Both were discovered while debugging lang/rust build failures with RUST_BACKTRACE=1 on FreeBSD/powerpc64le (IBM POWER9). On ppc64le, `unw_getcontext` saves each VS register with an in-place `xxswapd n, n` followed by `stxvd2x`. The swap is needed because `stxvd2x` stores doublewords in the wrong order on LE. However, the macro never applies a second `xxswapd` to restore the register after the store, so all 64 VS registers are permanently corrupted on return from `unw_getcontext`. This affects every callee-saved VSX register: f14-f31 (VSR14-VSR31) and VR20-VR31 (VSR52-VSR63). After `_Unwind_Backtrace` returns, any code that uses these registers sees wrong values. In practice this manifests as SIGSEGV inside hashbrown's `reserve_rehash`: VR20-VR31 are corrupted before a SIMD comparison loop runs, producing an out-of-bounds access. Fix: add a second `xxswapd n, n` after the `stxvd2x` store. Since `xxswapd` is its own inverse, the pair is a no-op on the architectural register while still writing the correctly byte-swapped value to memory. MFC after: 1 week --- contrib/llvm-project/libunwind/src/UnwindRegistersSave.S | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/contrib/llvm-project/libunwind/src/UnwindRegistersSave.S b/contrib/llvm-project/libunwind/src/UnwindRegistersSave.S index 5139a551ad24..bd41dfcb9db4 100644 --- a/contrib/llvm-project/libunwind/src/UnwindRegistersSave.S +++ b/contrib/llvm-project/libunwind/src/UnwindRegistersSave.S @@ -418,9 +418,13 @@ LnoR2Fix: // register in the incorrect doubleword order. // FIXME: when supporting targets older than Power9 on LE is no longer required // this can be changed to simply `stxv n, 16 * n(4)`. +// Restore the register after storing: xxswapd is its own inverse, so a second +// xxswapd undoes the in-place corruption of callee-saved VSRs (f14-f31, +// VR20-VR31) that would otherwise persist after unw_getcontext returns. #define PPC64_STVS(n) \ xxswapd n, n ;\ stxvd2x n, 0, 4 ;\ + xxswapd n, n ;\ addi 4, 4, 16 #else #define PPC64_STVS(n) \home | help
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