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[runtimes] Use LLVM libunwind from libc++abi by default #77687

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Merged
merged 4 commits into from
Jan 11, 2024
Merged

[runtimes] Use LLVM libunwind from libc++abi by default #77687

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6235f49
[runtimes] Use LLVM libunwind from libc++abi and compiler-rt by default
ldionne Jan 10, 2024
e2ce9b7
Disable the LLVM unwinder for Android
ldionne Jan 10, 2024
8f440fe
Don't touch compiler-rt
ldionne Jan 10, 2024
632f0c2
Merge branch 'main' into review/use-llvm-unwinder-by-default
ldionne Jan 10, 2024
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1 change: 0 additions & 1 deletion .github/workflows/libcxx-build-and-test.yaml
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Expand Up @@ -163,7 +163,6 @@ jobs:
'generic-no-rtti',
'generic-optimized-speed',
'generic-static',
'generic-with_llvm_unwinder',
# TODO Find a better place for the benchmark and bootstrapping builds to live. They're either very expensive
# or don't provide much value since the benchmark run results are too noise on the bots.
'benchmarks',
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2 changes: 1 addition & 1 deletion libcxx/CMakeLists.txt
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Expand Up @@ -274,7 +274,7 @@ option(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS
libc++abi. Doing otherwise is an ODR violation." OFF)
# Build libc++abi with libunwind. We need this option to determine whether to
# link with libunwind or libgcc_s while running the test cases.
option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." ON)

# Target options --------------------------------------------------------------
option(LIBCXX_BUILD_32_BITS "Build 32 bit multilib libc++. This option is not supported anymore when building the runtimes. Please specify a full triple instead." ${LLVM_BUILD_32_BITS})
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1 change: 0 additions & 1 deletion libcxx/cmake/caches/AArch64.cmake
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@@ -1,2 +1 @@
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(CMAKE_CXX_COMPILER_TARGET "aarch64-linux-gnu" CACHE STRING "")
1 change: 0 additions & 1 deletion libcxx/cmake/caches/AIX.cmake
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Expand Up @@ -13,6 +13,5 @@ set(LIBCXX_ENABLE_STATIC OFF CACHE BOOL "")
set(LIBCXXABI_ENABLE_SHARED ON CACHE BOOL "")
set(LIBCXXABI_ENABLE_STATIC OFF CACHE BOOL "")
set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(LIBUNWIND_ENABLE_SHARED ON CACHE BOOL "")
set(LIBUNWIND_ENABLE_STATIC OFF CACHE BOOL "")
3 changes: 3 additions & 0 deletions libcxx/cmake/caches/AndroidNDK.cmake
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Expand Up @@ -22,6 +22,9 @@ set(LIBCXX_ENABLE_ABI_LINKER_SCRIPT OFF CACHE BOOL "")
set(LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY ON CACHE BOOL "")
set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")

# Android uses its own unwinder library
set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "")
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Hmm. The Android runtime unwinder is also LLVM libunwind; is there any harm in building and using our own instead of the NDK's? CC @rprichard

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The Android NDK currently sources all of libunwind, libc++abi, and libc++ from the same LLVM commit, so maybe it's better to build the unwinder library at the same time as libc++.

OTOH, Android's libc.so exports libunwind's EH API as of API 30 (Android 11), so eventually the NDK might be using an unwinder that's from a much older LLVM commit. It'll be a long time before the NDK targets API 30 as a minimum.

IIRC, when I last looked at the Linux libc++ CI tests (i.e. non-Android), the LLVM libunwind was built in the same runtimes CMake invocation as libc++, but the result wasn't actually used or tested. When I set up Android CI testing, I initially had it build libunwind as part of the CI testing, but I wanted the result to resemble what the NDK actually ships, which required a separate step for libunwind (and patching the result into a new resource dir) (see https://reviews.llvm.org/D139147?id=549856, search for "Build libunwind.a"). This patching was dropped in favor of using a libunwind.a from an Android Clang build.


# Clang links libc++ by default, but it doesn't exist yet. The libc++ CMake
# files specify -nostdlib++ to avoid this problem, but CMake's default "compiler
# works" testing doesn't pass that flag, so force those tests to pass.
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1 change: 1 addition & 0 deletions libcxx/cmake/caches/Apple.cmake
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Expand Up @@ -14,6 +14,7 @@ set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")

set(LIBCXXABI_ENABLE_ASSERTIONS OFF CACHE BOOL "")
set(LIBCXXABI_ENABLE_FORGIVING_DYNAMIC_CAST ON CACHE BOOL "")
set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # libunwind is built separately

set(LIBCXX_TEST_CONFIG "apple-libc++-shared.cfg.in" CACHE STRING "")
set(LIBCXXABI_TEST_CONFIG "apple-libc++abi-shared.cfg.in" CACHE STRING "")
1 change: 0 additions & 1 deletion libcxx/cmake/caches/Armv7Arm.cmake
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@@ -1,4 +1,3 @@
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(CMAKE_CXX_COMPILER_TARGET "armv7l-linux-gnueabihf" CACHE STRING "")
set(CMAKE_CXX_FLAGS "-marm" CACHE STRING "")
set(CMAKE_C_FLAGS "-marm" CACHE STRING "")
1 change: 0 additions & 1 deletion libcxx/cmake/caches/Armv7M-picolibc.cmake
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Expand Up @@ -19,7 +19,6 @@ set(LIBCXXABI_ENABLE_STATIC ON CACHE BOOL "")
set(LIBCXXABI_ENABLE_STATIC_UNWINDER ON CACHE BOOL "")
set(LIBCXXABI_ENABLE_THREADS OFF CACHE BOOL "")
set(LIBCXXABI_USE_COMPILER_RT ON CACHE BOOL "")
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(LIBCXX_ENABLE_EXCEPTIONS ON CACHE BOOL "")
set(LIBCXX_ENABLE_FILESYSTEM OFF CACHE STRING "")
set(LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
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1 change: 0 additions & 1 deletion libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
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@@ -1,4 +1,3 @@
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(CMAKE_CXX_COMPILER_TARGET "armv7l-linux-gnueabihf" CACHE STRING "")
set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
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1 change: 0 additions & 1 deletion libcxx/cmake/caches/Armv8Arm.cmake
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@@ -1,4 +1,3 @@
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(CMAKE_CXX_COMPILER_TARGET "armv8l-linux-gnueabihf" CACHE STRING "")
set(CMAKE_CXX_FLAGS "-marm" CACHE STRING "")
set(CMAKE_C_FLAGS "-marm" CACHE STRING "")
1 change: 0 additions & 1 deletion libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
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@@ -1,4 +1,3 @@
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(CMAKE_CXX_COMPILER_TARGET "armv8l-linux-gnueabihf" CACHE STRING "")
set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
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1 change: 0 additions & 1 deletion libcxx/cmake/caches/Generic-merged.cmake
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Expand Up @@ -5,7 +5,6 @@ set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
set(LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY ON CACHE BOOL "")

set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
set(LIBCXXABI_ENABLE_STATIC_UNWINDER ON CACHE BOOL "")
set(LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY ON CACHE BOOL "")

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1 change: 1 addition & 0 deletions libcxx/cmake/caches/Generic-msan.cmake
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@@ -1 +1,2 @@
set(LLVM_USE_SANITIZER "MemoryWithOrigins" CACHE STRING "")
set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # MSAN is compiled against the system unwinder, which leads to false positives
1 change: 1 addition & 0 deletions libcxx/cmake/caches/Generic-tsan.cmake
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@@ -1 +1,2 @@
set(LLVM_USE_SANITIZER "Thread" CACHE STRING "")
set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # TSAN is compiled against the system unwinder, which leads to false positives
1 change: 0 additions & 1 deletion libcxx/cmake/caches/MinGW.cmake
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@@ -1,5 +1,4 @@
set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")

set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
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2 changes: 1 addition & 1 deletion libcxx/docs/BuildingLibcxx.rst
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Expand Up @@ -337,7 +337,7 @@ ABI Library Specific Options

.. option:: LIBCXXABI_USE_LLVM_UNWINDER:BOOL

**Default**: ``OFF``
**Default**: ``ON``

Build and use the LLVM unwinder. Note: This option can only be used when
libc++abi is the C++ ABI library used.
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7 changes: 7 additions & 0 deletions libcxx/docs/ReleaseNotes/18.rst
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Expand Up @@ -191,3 +191,10 @@ Build System Changes
passing ``-Dexecutor=...`` to ``llvm-lit``. Alternatively, this flag can be made persistent in the generated test
configuration file by passing ``-DLIBCXX_TEST_PARAMS=executor=...``. This also applies to the ``LIBUWIND_EXECTOR``
and ``LIBCXXABI_EXECUTOR`` CMake variables. LLVM 19 will completely remove support for the ``*_EXECUTOR`` variables.

- ``LIBCXXABI_USE_LLVM_UNWINDER`` and ``COMPILER_RT_USE_LLVM_UNWINDER`` switched defaults from ``OFF`` to ``ON``.
This means that by default, libc++abi and compiler-rt will link against the LLVM provided ``libunwind`` library
instead of the system-provided unwinding library. If you are building the LLVM runtimes with the goal of shipping
them so that they can interoperate with other system-provided libraries that might be using a different unwinding
library (such as ``libgcc_s``), you should pass ``LIBCXXABI_USE_LLVM_UNWINDER=OFF`` and ``COMPILER_RT_USE_LLVM_UNWINDER=OFF``
to make sure the system-provided unwinding library is used by the LLVM runtimes.
5 changes: 0 additions & 5 deletions libcxx/utils/ci/run-buildbot
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Expand Up @@ -439,11 +439,6 @@ generic-hardening-mode-debug)
check-runtimes
check-abi-list
;;
generic-with_llvm_unwinder)
clean
generate-cmake -DLIBCXXABI_USE_LLVM_UNWINDER=ON
check-runtimes
;;
#
# Module builds
#
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2 changes: 1 addition & 1 deletion libcxxabi/CMakeLists.txt
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Expand Up @@ -46,7 +46,7 @@ option(LIBCXXABI_ENABLE_EXCEPTIONS
option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." ON)
option(LIBCXXABI_ENABLE_STATIC_UNWINDER "Statically link the LLVM unwinder." OFF)
option(LIBCXXABI_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
option(LIBCXXABI_ENABLE_THREADS "Build with threads enabled" ON)
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