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Fix aarch64 SIGILL: disable mimalloc LSE atomics + update WebKit + QEMU verification (#26586)

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Fixes illegal instruction (SIGILL) crashes on ARMv8.0 aarch64 CPUs
(Cortex-A53, Raspberry Pi 4, AWS a1 instances).

## Root cause

Upstream mimalloc force-enables `MI_OPT_ARCH` on arm64, which adds
`-march=armv8.1-a` and emits LSE atomic instructions (`casa`, `swpa`,
`ldaddl`). These are not available on ARMv8.0 CPUs.

## Fix

- Pass `MI_NO_OPT_ARCH=ON` to mimalloc on aarch64 (has priority over
`MI_OPT_ARCH` in mimalloc's CMake)
- Update WebKit to autobuild-596e48e22e3a1090e5b802744a7938088b1ea860
which explicitly passes `-march` flags to the WebKit build

## Verification

Includes QEMU-based baseline CPU verification CI steps (#26571) that
catch these regressions automatically.
This commit is contained in:
Dylan Conway
2026-01-29 17:18:57 -08:00
committed by GitHub
parent 8a11a03297
commit adc1a6b05c
2 changed files with 13 additions and 3 deletions
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14
cmake/targets/BuildMimalloc.cmake
View File

@@ -69,8 +69,18 @@ if(ENABLE_VALGRIND)
list(APPEND MIMALLOC_CMAKE_ARGS -DMI_VALGRIND=ON)
endif()
# Enable SIMD optimizations when not building for baseline (older CPUs)
if(NOT ENABLE_BASELINE)
# Enable architecture-specific optimizations when not building for baseline.
# On Linux aarch64, upstream mimalloc force-enables MI_OPT_ARCH which adds
# -march=armv8.1-a (LSE atomics). This crashes on ARMv8.0 CPUs
# (Cortex-A53, Raspberry Pi 4, AWS a1 instances). Use MI_NO_OPT_ARCH
# to prevent that, but keep SIMD enabled. -moutline-atomics for runtime
# dispatch to LSE/LL-SC. macOS arm64 always has LSE (Apple Silicon) so
# MI_OPT_ARCH is safe there.
if(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64|arm64|ARM64|AARCH64" AND NOT APPLE)
list(APPEND MIMALLOC_CMAKE_ARGS -DMI_NO_OPT_ARCH=ON)
list(APPEND MIMALLOC_CMAKE_ARGS -DMI_OPT_SIMD=ON)
list(APPEND MIMALLOC_CMAKE_ARGS "-DCMAKE_C_FLAGS=-moutline-atomics")
elseif(NOT ENABLE_BASELINE)
list(APPEND MIMALLOC_CMAKE_ARGS -DMI_OPT_ARCH=ON)
list(APPEND MIMALLOC_CMAKE_ARGS -DMI_OPT_SIMD=ON)
endif()

2
cmake/tools/SetupWebKit.cmake
View File

@@ -2,7 +2,7 @@ option(WEBKIT_VERSION "The version of WebKit to use")
option(WEBKIT_LOCAL "If a local version of WebKit should be used instead of downloading")
if(NOT WEBKIT_VERSION)
set(WEBKIT_VERSION 9a2cc42ae1bf693a0fd0ceb9b1d7d965d9cfd3ea)
set(WEBKIT_VERSION 515344bc5d65aa2d4f9ff277b5fb944f0e051dcd)
endif()
# Use preview build URL for Windows ARM64 until the fix is merged to main