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

ldionne · 2024-01-10T21:08:30Z

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any).

Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired.

As a follow-up change, we should probably apply the same default to compiler-rt.

Differential Revision: https://reviews.llvm.org/D150897
Fixes #77662
rdar://120801778

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any). Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired. Differential Revision: https://reviews.llvm.org/D150897 Fixes llvm#77662 rdar://120801778

llvmbot · 2024-01-10T21:08:57Z

@llvm/pr-subscribers-libcxxabi

@llvm/pr-subscribers-github-workflow

Author: Louis Dionne (ldionne)

Changes

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any).

Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired.

Differential Revision: https://reviews.llvm.org/D150897
Fixes #77662
rdar://120801778

Full diff: https://github.com/llvm/llvm-project/pull/77687.diff

19 Files Affected:

(modified) .github/workflows/libcxx-build-and-test.yaml (-1)
(modified) compiler-rt/CMakeLists.txt (+1-1)
(modified) libcxx/CMakeLists.txt (+1-1)
(modified) libcxx/cmake/caches/AArch64.cmake (-1)
(modified) libcxx/cmake/caches/AIX.cmake (-1)
(modified) libcxx/cmake/caches/Apple.cmake (+1)
(modified) libcxx/cmake/caches/Armv7Arm.cmake (-1)
(modified) libcxx/cmake/caches/Armv7M-picolibc.cmake (-1)
(modified) libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake (-1)
(modified) libcxx/cmake/caches/Armv8Arm.cmake (-1)
(modified) libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake (-1)
(modified) libcxx/cmake/caches/Generic-merged.cmake (-1)
(modified) libcxx/cmake/caches/Generic-msan.cmake (+1)
(modified) libcxx/cmake/caches/Generic-tsan.cmake (+1)
(modified) libcxx/cmake/caches/MinGW.cmake (-1)
(modified) libcxx/docs/BuildingLibcxx.rst (+1-1)
(modified) libcxx/docs/ReleaseNotes/18.rst (+7)
(modified) libcxx/utils/ci/run-buildbot (-5)
(modified) libcxxabi/CMakeLists.txt (+1-1)

diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index 985790a0ee2361..1666a687aa5d04 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -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',
diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
index bbb4e8d7c333e4..ff6e4347b80b39 100644
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -229,7 +229,7 @@ set(CXXLIBS none default libstdc++ libc++)
 set_property(CACHE SANITIZER_TEST_CXX PROPERTY STRINGS ;${CXXLIBS})
 handle_default_cxx_lib(SANITIZER_TEST_CXX)
 
-option(COMPILER_RT_USE_LLVM_UNWINDER "Use the LLVM unwinder." OFF)
+option(COMPILER_RT_USE_LLVM_UNWINDER "Use the LLVM unwinder." ON)
 cmake_dependent_option(COMPILER_RT_ENABLE_STATIC_UNWINDER
   "Statically link the LLVM unwinder." OFF
   "COMPILER_RT_USE_LLVM_UNWINDER" OFF)
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 75cb63222da35c..cf197d8c224143 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -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})
diff --git a/libcxx/cmake/caches/AArch64.cmake b/libcxx/cmake/caches/AArch64.cmake
index fa802d3de63f04..d813273584b0f0 100644
--- a/libcxx/cmake/caches/AArch64.cmake
+++ b/libcxx/cmake/caches/AArch64.cmake
@@ -1,2 +1 @@
-set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
 set(CMAKE_CXX_COMPILER_TARGET "aarch64-linux-gnu" CACHE STRING "")
diff --git a/libcxx/cmake/caches/AIX.cmake b/libcxx/cmake/caches/AIX.cmake
index 31d9a2d4b72751..c01aa5b14df065 100644
--- a/libcxx/cmake/caches/AIX.cmake
+++ b/libcxx/cmake/caches/AIX.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Apple.cmake b/libcxx/cmake/caches/Apple.cmake
index 804eccd3a5dc5e..cec13c08acf107 100644
--- a/libcxx/cmake/caches/Apple.cmake
+++ b/libcxx/cmake/caches/Apple.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7Arm.cmake b/libcxx/cmake/caches/Armv7Arm.cmake
index 4d18d08fefcd22..e60d43f33dde7f 100644
--- a/libcxx/cmake/caches/Armv7Arm.cmake
+++ b/libcxx/cmake/caches/Armv7Arm.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7M-picolibc.cmake b/libcxx/cmake/caches/Armv7M-picolibc.cmake
index 3ab80b960ed44a..b5f9089308d22e 100644
--- a/libcxx/cmake/caches/Armv7M-picolibc.cmake
+++ b/libcxx/cmake/caches/Armv7M-picolibc.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
index 71173af106b637..70b619f8ec31f3 100644
--- a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv8Arm.cmake b/libcxx/cmake/caches/Armv8Arm.cmake
index 5055582fdafc0d..a2894716035304 100644
--- a/libcxx/cmake/caches/Armv8Arm.cmake
+++ b/libcxx/cmake/caches/Armv8Arm.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
index 316edd31490665..b4c7dfca279cd3 100644
--- a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Generic-merged.cmake b/libcxx/cmake/caches/Generic-merged.cmake
index b2e02f73105557..7ebb8026236ddf 100644
--- a/libcxx/cmake/caches/Generic-merged.cmake
+++ b/libcxx/cmake/caches/Generic-merged.cmake
@@ -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 "")
 
diff --git a/libcxx/cmake/caches/Generic-msan.cmake b/libcxx/cmake/caches/Generic-msan.cmake
index 7c948f51642dd4..9e50255fe4ff6b 100644
--- a/libcxx/cmake/caches/Generic-msan.cmake
+++ b/libcxx/cmake/caches/Generic-msan.cmake
@@ -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
diff --git a/libcxx/cmake/caches/Generic-tsan.cmake b/libcxx/cmake/caches/Generic-tsan.cmake
index a4b599e3e5094b..c42c1bb8e72221 100644
--- a/libcxx/cmake/caches/Generic-tsan.cmake
+++ b/libcxx/cmake/caches/Generic-tsan.cmake
@@ -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
diff --git a/libcxx/cmake/caches/MinGW.cmake b/libcxx/cmake/caches/MinGW.cmake
index a5927096d8ff96..09e6ea5c1bab20 100644
--- a/libcxx/cmake/caches/MinGW.cmake
+++ b/libcxx/cmake/caches/MinGW.cmake
@@ -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 "")
diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst
index 0b4d4205286512..f2304c9796b540 100644
--- a/libcxx/docs/BuildingLibcxx.rst
+++ b/libcxx/docs/BuildingLibcxx.rst
@@ -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.
diff --git a/libcxx/docs/ReleaseNotes/18.rst b/libcxx/docs/ReleaseNotes/18.rst
index 5df6242e52317a..478e87f8888332 100644
--- a/libcxx/docs/ReleaseNotes/18.rst
+++ b/libcxx/docs/ReleaseNotes/18.rst
@@ -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.
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index ed2bc2a14f17d6..0ff028743bc1a3 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -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
 #
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index efe830bd2ad665..c62b05bf2feafc 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -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)

llvmbot · 2024-01-10T21:08:57Z

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

Changes

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any).

Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired.

Differential Revision: https://reviews.llvm.org/D150897
Fixes #77662
rdar://120801778

Full diff: https://github.com/llvm/llvm-project/pull/77687.diff

19 Files Affected:

(modified) .github/workflows/libcxx-build-and-test.yaml (-1)
(modified) compiler-rt/CMakeLists.txt (+1-1)
(modified) libcxx/CMakeLists.txt (+1-1)
(modified) libcxx/cmake/caches/AArch64.cmake (-1)
(modified) libcxx/cmake/caches/AIX.cmake (-1)
(modified) libcxx/cmake/caches/Apple.cmake (+1)
(modified) libcxx/cmake/caches/Armv7Arm.cmake (-1)
(modified) libcxx/cmake/caches/Armv7M-picolibc.cmake (-1)
(modified) libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake (-1)
(modified) libcxx/cmake/caches/Armv8Arm.cmake (-1)
(modified) libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake (-1)
(modified) libcxx/cmake/caches/Generic-merged.cmake (-1)
(modified) libcxx/cmake/caches/Generic-msan.cmake (+1)
(modified) libcxx/cmake/caches/Generic-tsan.cmake (+1)
(modified) libcxx/cmake/caches/MinGW.cmake (-1)
(modified) libcxx/docs/BuildingLibcxx.rst (+1-1)
(modified) libcxx/docs/ReleaseNotes/18.rst (+7)
(modified) libcxx/utils/ci/run-buildbot (-5)
(modified) libcxxabi/CMakeLists.txt (+1-1)

diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index 985790a0ee2361..1666a687aa5d04 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -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',
diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
index bbb4e8d7c333e4..ff6e4347b80b39 100644
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -229,7 +229,7 @@ set(CXXLIBS none default libstdc++ libc++)
 set_property(CACHE SANITIZER_TEST_CXX PROPERTY STRINGS ;${CXXLIBS})
 handle_default_cxx_lib(SANITIZER_TEST_CXX)
 
-option(COMPILER_RT_USE_LLVM_UNWINDER "Use the LLVM unwinder." OFF)
+option(COMPILER_RT_USE_LLVM_UNWINDER "Use the LLVM unwinder." ON)
 cmake_dependent_option(COMPILER_RT_ENABLE_STATIC_UNWINDER
   "Statically link the LLVM unwinder." OFF
   "COMPILER_RT_USE_LLVM_UNWINDER" OFF)
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 75cb63222da35c..cf197d8c224143 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -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})
diff --git a/libcxx/cmake/caches/AArch64.cmake b/libcxx/cmake/caches/AArch64.cmake
index fa802d3de63f04..d813273584b0f0 100644
--- a/libcxx/cmake/caches/AArch64.cmake
+++ b/libcxx/cmake/caches/AArch64.cmake
@@ -1,2 +1 @@
-set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
 set(CMAKE_CXX_COMPILER_TARGET "aarch64-linux-gnu" CACHE STRING "")
diff --git a/libcxx/cmake/caches/AIX.cmake b/libcxx/cmake/caches/AIX.cmake
index 31d9a2d4b72751..c01aa5b14df065 100644
--- a/libcxx/cmake/caches/AIX.cmake
+++ b/libcxx/cmake/caches/AIX.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Apple.cmake b/libcxx/cmake/caches/Apple.cmake
index 804eccd3a5dc5e..cec13c08acf107 100644
--- a/libcxx/cmake/caches/Apple.cmake
+++ b/libcxx/cmake/caches/Apple.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7Arm.cmake b/libcxx/cmake/caches/Armv7Arm.cmake
index 4d18d08fefcd22..e60d43f33dde7f 100644
--- a/libcxx/cmake/caches/Armv7Arm.cmake
+++ b/libcxx/cmake/caches/Armv7Arm.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7M-picolibc.cmake b/libcxx/cmake/caches/Armv7M-picolibc.cmake
index 3ab80b960ed44a..b5f9089308d22e 100644
--- a/libcxx/cmake/caches/Armv7M-picolibc.cmake
+++ b/libcxx/cmake/caches/Armv7M-picolibc.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
index 71173af106b637..70b619f8ec31f3 100644
--- a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv8Arm.cmake b/libcxx/cmake/caches/Armv8Arm.cmake
index 5055582fdafc0d..a2894716035304 100644
--- a/libcxx/cmake/caches/Armv8Arm.cmake
+++ b/libcxx/cmake/caches/Armv8Arm.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
index 316edd31490665..b4c7dfca279cd3 100644
--- a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
@@ -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 "")
diff --git a/libcxx/cmake/caches/Generic-merged.cmake b/libcxx/cmake/caches/Generic-merged.cmake
index b2e02f73105557..7ebb8026236ddf 100644
--- a/libcxx/cmake/caches/Generic-merged.cmake
+++ b/libcxx/cmake/caches/Generic-merged.cmake
@@ -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 "")
 
diff --git a/libcxx/cmake/caches/Generic-msan.cmake b/libcxx/cmake/caches/Generic-msan.cmake
index 7c948f51642dd4..9e50255fe4ff6b 100644
--- a/libcxx/cmake/caches/Generic-msan.cmake
+++ b/libcxx/cmake/caches/Generic-msan.cmake
@@ -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
diff --git a/libcxx/cmake/caches/Generic-tsan.cmake b/libcxx/cmake/caches/Generic-tsan.cmake
index a4b599e3e5094b..c42c1bb8e72221 100644
--- a/libcxx/cmake/caches/Generic-tsan.cmake
+++ b/libcxx/cmake/caches/Generic-tsan.cmake
@@ -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
diff --git a/libcxx/cmake/caches/MinGW.cmake b/libcxx/cmake/caches/MinGW.cmake
index a5927096d8ff96..09e6ea5c1bab20 100644
--- a/libcxx/cmake/caches/MinGW.cmake
+++ b/libcxx/cmake/caches/MinGW.cmake
@@ -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 "")
diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst
index 0b4d4205286512..f2304c9796b540 100644
--- a/libcxx/docs/BuildingLibcxx.rst
+++ b/libcxx/docs/BuildingLibcxx.rst
@@ -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.
diff --git a/libcxx/docs/ReleaseNotes/18.rst b/libcxx/docs/ReleaseNotes/18.rst
index 5df6242e52317a..478e87f8888332 100644
--- a/libcxx/docs/ReleaseNotes/18.rst
+++ b/libcxx/docs/ReleaseNotes/18.rst
@@ -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.
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index ed2bc2a14f17d6..0ff028743bc1a3 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -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
 #
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index efe830bd2ad665..c62b05bf2feafc 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -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)

MaskRay

This looks like a simplified version of https://reviews.llvm.org/D150897 that does not remove redundant LIBCXXABI_USE_LLVM_UNWINDER ON. LGTM but I think some docs/ changes are needed.

edit: This change now includes all of https://reviews.llvm.org/D150897 . LGTM!

ldionne · 2024-01-11T15:50:39Z

@vitalybuka This seems to have broken the ASAN and HWASAN builds here:
https://lab.llvm.org/buildbot/#/builders/236/builds/8629/steps/8/logs/stdio
https://lab.llvm.org/buildbot/#/builders/168/builds/17965/steps/8/logs/stdio

My understanding is that we'd now need to either explicitly say LIBCXXABI_USE_LLVM_UNWINDER=OFF or we'd need to change to -DLLVM_ENABLE_RUNTIMES='libcxx;libcxxabi;libunwind' here in buildbot_functions.sh.

Edit: See llvm/llvm-zorg#96

See llvm/llvm-project#77687 for more details.

vitalybuka · 2024-01-11T21:11:28Z

@vitalybuka This seems to have broken the ASAN and HWASAN builds here: https://lab.llvm.org/buildbot/#/builders/236/builds/8629/steps/8/logs/stdio https://lab.llvm.org/buildbot/#/builders/168/builds/17965/steps/8/logs/stdio

My understanding is that we'd now need to either explicitly say LIBCXXABI_USE_LLVM_UNWINDER=OFF or we'd need to change to -DLLVM_ENABLE_RUNTIMES='libcxx;libcxxabi;libunwind' here in buildbot_functions.sh.

Edit: See llvm/llvm-zorg#96

Thanks for the patch, I will followup and recover buildbots

smeenai · 2024-01-11T22:12:34Z

libcxx/cmake/caches/AndroidNDK.cmake

@@ -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 "")


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

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.

vitalybuka · 2024-01-11T22:31:38Z

@ldionne @MaskRay
Any ideas what does this mean https://lab.llvm.org/buildbot/#/builders/85/builds/21530

MaskRay · 2024-01-11T22:39:48Z

@ldionne @MaskRay Any ideas what does this mean lab.llvm.org/buildbot/#/builders/85/builds/21530

This looks like a fatal runtime error for the test test/ExecutionEngine/MCJIT/Output/eh.ll related to OrcJIT. It seems unrelated to compiler-rt/lib/orc/elfnix_platform.cpp. I think it is perhaps related to existing OrcJIT instability, happened to be uncovered by this CMake change.

GTEST_OUTPUT=json:/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/unittests/Interpreter/ExceptionTests/./ClangReplInterpreterExceptionTests-Clang-Unit-2380782-0-1.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=1 GTEST_SHARD_INDEX=0 /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/unittests/Interpreter/ExceptionTests/./ClangReplInterpreterExceptionTests
--
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from InterpreterTest
[ RUN      ] InterpreterTest.CatchException
libunwind: __unw_add_dynamic_fde: bad fde: FDE is really a CIE
libc++abi: terminating due to uncaught exception of type custom_exception
 #0 0x000055c0558128ce llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:723:13
 #1 0x000055c05580f716 llvm::sys::RunSignalHandlers() /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Signals.cpp:106:18
 #2 0x000055c05581333f SignalHandler(int) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:413:1
 #3 0x00007fac4963c460 (/lib/x86_64-linux-gnu/libc.so.6+0x3c460)
 #4 0x00007fac4969152b pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9152b)
 #5 0x00007fac4963c3b6 raise (/lib/x86_64-linux-gnu/libc.so.6+0x3c3b6)
 #6 0x00007fac4962287c abort (/lib/x86_64-linux-gnu/libc.so.6+0x2287c)
 #7 0x00007fac499d0edb abort_message /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/abort_message.cpp:78:5
 #8 0x00007fac499a43c6 demangling_terminate_handler() /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_default_handlers.cpp:77:9
 #9 0x00007fac499cf812 std::__terminate(void (*)()) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_handlers.cpp:61:9
#10 0x00007fac499d9ba7 __cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:152:5
#11 0x00007fac499d9761 cxa_exception_from_thrown_object /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:45:57
#12 0x00007fac499d9761 __cxa_throw /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:264:41
#13 0x00007fac49cc40f9

llvm/llvm-project#77687 enabled libunwind, but not all tests pass with sanitizers. So disable libunwind to investigate.

Revert "[runtimes] Use LLVM libunwind from libc++abi by default (llvm#77687)" Change-Id: I20ac6cae4f6d4469a0c0de4157a3faf5463d1752

vitalybuka · 2024-01-12T19:53:53Z

@petrhosek @ldionne
would it be better detect libunwind in LLVM_ENABLE_RUNTIMES?

Asking because we have similar thing in compiler-rt, e.g. for lld, and I am not sure which approach is better:
There are trade offs:

checking LLVM_ENABLE_RUNTIMES simplify end user experience
forcing default ON simplifies cmake files and avoids unexpected use of system lib

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any). Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired. As a follow-up change, we should probably apply the same default to compiler-rt. Differential Revision: https://reviews.llvm.org/D150897 Fixes llvm#77662 rdar://120801778 Change-Id: Id2a0483ca5b032faec2d5c81753aea9a08695b4f

ref: llvm/llvm-project#77687

mgorny · 2024-01-13T16:28:39Z

FTR, this breaks standalone builds against installed LLVM's libunwind since unwind_shared target doesn't exist. However, as long as I can pass -DLIBCXXABI_USE_LLVM_UNWINDER=OFF that just does the right thing, it's fine with me.

cor3ntin · 2024-01-15T10:48:58Z

FYI, This affects compiler explorer builds (trunk no longer builds)

libunwind is now necessary to build libc++ llvm/llvm-project#77687 (comment)

libunwind is required to build libc++ as of llvm/llvm-project#77687 (comment) It was already used for numbered versions, but not trunk. I also updated my branch and left everything else alone as I did not know whether they use version of clang that can build libunwind

ldionne · 2024-01-15T15:20:08Z

@petrhosek @ldionne would it be better detect libunwind in LLVM_ENABLE_RUNTIMES?

I added a check in CMake here: #77991. The error message should now be clearer than previously.

petrhosek · 2024-01-16T09:25:13Z

@petrhosek @ldionne would it be better detect libunwind in LLVM_ENABLE_RUNTIMES?

Asking because we have similar thing in compiler-rt, e.g. for lld, and I am not sure which approach is better: There are trade offs:

checking LLVM_ENABLE_RUNTIMES simplify end user experience

forcing default ON simplifies cmake files and avoids unexpected use of system lib

That would be my preference, specifically I'd set the default for LIBCXXABI_USE_LLVM_UNWINDER based on whether libunwind is present in LLVM_ENABLE_RUNTIMES (but still let user override it).

ldionne · 2024-01-16T13:29:27Z

That means that based on whether LLVM_ENABLE_RUNTIMES=libunwind happens to be set or not, you'd use a fundamentally different unwinding library which implies a different ABI. It's convenient, but isn't that too subtle?

mordante · 2024-01-16T20:11:57Z

FYI I think this change broke the documentation CI builder. Fixed in 7e909d5

I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to notice it was disabled by default. Since we build libunwind by default and ship it in the LLVM toolchain, it would seem to make sense that libc++ and libc++abi rely on libunwind for unwinding instead of using the system-provided unwinding library (if any). Most importantly, using the system unwinder implies that libc++abi is ABI compatible with that system unwinder, which is not necessarily the case. Hence, it makes a lot more sense to instead default to using the known-to-be-compatible LLVM unwinder, and let vendors manually select a different unwinder if desired. As a follow-up change, we should probably apply the same default to compiler-rt. Differential Revision: https://reviews.llvm.org/D150897 Fixes llvm#77662 rdar://120801778

ldionne requested review from a team as code owners January 10, 2024 21:08

llvmbot added compiler-rt libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. libc++abi libc++abi C++ Runtime Library. Not libc++. github:workflow labels Jan 10, 2024

ldionne requested review from petrhosek and MaskRay January 10, 2024 21:08

ldionne added 2 commits January 10, 2024 16:22

Disable the LLVM unwinder for Android

e2ce9b7

Don't touch compiler-rt

8f440fe

ldionne changed the title ~~[runtimes] Use LLVM libunwind from libc++abi and compiler-rt by default~~ [runtimes] Use LLVM libunwind from libc++abi by default Jan 10, 2024

Merge branch 'main' into review/use-llvm-unwinder-by-default

632f0c2

MaskRay approved these changes Jan 11, 2024

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petrhosek approved these changes Jan 11, 2024

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ldionne merged commit 8f90e69 into llvm:main Jan 11, 2024
44 checks passed

ldionne deleted the review/use-llvm-unwinder-by-default branch January 11, 2024 15:13

ldionne added a commit to ldionne/llvm-zorg that referenced this pull request Jan 11, 2024

[sanitizers] Ensure we build LLVM's libunwind with the sanitizers

c4340a4

See llvm/llvm-project#77687 for more details.

ldionne mentioned this pull request Jan 11, 2024

[sanitizers] Ensure we build LLVM's libunwind with the sanitizers llvm/llvm-zorg#96

Merged

vitalybuka pushed a commit to llvm/llvm-zorg that referenced this pull request Jan 11, 2024

[sanitizers] Ensure we build LLVM's libunwind with the sanitizers (#96)

10993ce

See llvm/llvm-project#77687 for more details.

smeenai reviewed Jan 11, 2024

View reviewed changes

ye-luo mentioned this pull request Jan 11, 2024

[libc++abi] lack of the detection of libunwind library files. #77843

Closed

vitalybuka added a commit to llvm/llvm-zorg that referenced this pull request Jan 12, 2024

Disabled libunwind, #96 was not enough

23cd70e

llvm/llvm-project#77687 enabled libunwind, but not all tests pass with sanitizers. So disable libunwind to investigate.

searlmc1 pushed a commit to ROCm/llvm-project that referenced this pull request Jan 12, 2024

merge main into amd-staging

9f8bc08

Revert "[runtimes] Use LLVM libunwind from libc++abi by default (llvm#77687)" Change-Id: I20ac6cae4f6d4469a0c0de4157a3faf5463d1752

melpon added a commit to melpon/wandbox-builder that referenced this pull request Jan 13, 2024

libunwind を利用する

b788bb3

ref: llvm/llvm-project#77687

cor3ntin added a commit to cor3ntin/clang-builder that referenced this pull request Jan 15, 2024

Make sure libunwind is enabled for recent clamg version

811b3be

libunwind is now necessary to build libc++ llvm/llvm-project#77687 (comment)

cor3ntin mentioned this pull request Jan 15, 2024

Use libunwind for recent clang versions compiler-explorer/clang-builder#58

Merged

itrofimow mentioned this pull request Jan 17, 2024

[libc++] [libc++abi] Initialize exception directly in make_exception_ptr if __cxa_init_primary_exception is available in ABI-library #65534

Merged

fhahn mentioned this pull request Jan 17, 2024

LIBCXXABI_USE_LLVM_UNWINDER=ON breaks PGO build #78487

Closed

wegank mentioned this pull request Feb 2, 2024

llvmPackages_git: 18.0.0-unstable-2023-12-13 -> 18.1.0-rc3 NixOS/nixpkgs#285786

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

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

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

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

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