The Hexagon-specific constant extender optimization in LLVM may crash on Linux kernel code [1], such as fs/bcache/btree_io.c after commit 32ed4a620c54 ("bcachefs: Btree path tracepoints") in 6.12:

clang: llvm/lib/Target/Hexagon/HexagonConstExtenders.cpp:745: bool (anonymous namespace)::HexagonConstExtenders::ExtRoot::operator<(const HCE::ExtRoot &) const: Assertion `ThisB->getParent() == OtherB->getParent()' failed. Stack dump: 0. Program arguments: clang --target=hexagon-linux-musl ... fs/bcachefs/btree_io.c 1. <eof> parser at end of file 2. Code generation 3. Running pass 'Function Pass Manager' on module 'fs/bcachefs/btree_io.c'. 4. Running pass 'Hexagon constant-extender optimization' on function '@__btree_node_lock_nopath'

Without assertions enabled, there is just a hang during compilation.

This has been resolved in LLVM main (20.0.0) [2] and backported to LLVM 19.1.0 but the kernel supports LLVM 13.0.1 and newer, so disable the constant expander optimization using the '-mllvm' option when using a toolchain that is not fixed.

Cc: stable@vger.kernel.org Link: https://github.com/llvm/llvm-project/issues/99714 [1] Link: https://github.com/llvm/llvm-project/commit/68df06a0b2998765cb0a41353fcf0919... [2] Link: https://github.com/llvm/llvm-project/commit/2ab8d93061581edad3501561722ebd56... [3] Reviewed-by: Brian Cain bcain@quicinc.com Signed-off-by: Nathan Chancellor nathan@kernel.org --- Andrew, can you please take this for 6.13? Our CI continues to hit this.

Changes in v2: - Rebase on 6.12 to make sure it is still applicable - Name exact bcachefs commit that introduces crash now that it is merged - Add 'Cc: stable' as this is now visible in a stable release - Carry forward Brian's reviewed-by - Link to v1: https://lore.kernel.org/r/20240819-hexagon-disable-constant-expander-pass-v1... --- arch/hexagon/Makefile | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/arch/hexagon/Makefile b/arch/hexagon/Makefile index 92d005958dfb232d48a4ca843b46262a84a08eb4..ff172cbe5881a074f9d9430c37071992a4c8beac 100644 --- a/arch/hexagon/Makefile +++ b/arch/hexagon/Makefile @@ -32,3 +32,9 @@ KBUILD_LDFLAGS += $(ldflags-y) TIR_NAME := r19 KBUILD_CFLAGS += -ffixed-$(TIR_NAME) -DTHREADINFO_REG=$(TIR_NAME) -D__linux__ KBUILD_AFLAGS += -DTHREADINFO_REG=$(TIR_NAME) + +# Disable HexagonConstExtenders pass for LLVM versions prior to 19.1.0 +# https://github.com/llvm/llvm-project/issues/99714 +ifneq ($(call clang-min-version, 190100),y) +KBUILD_CFLAGS += -mllvm -hexagon-cext=false +endif

--- base-commit: adc218676eef25575469234709c2d87185ca223a change-id: 20240802-hexagon-disable-constant-expander-pass-8b6b61db6afc

Best regards,