[libunwind] [libcxx] [libcxxabi] [runtimes] Don't link against compiler-rt explicitly when we use -nostdlib++ (PR #75089)
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Mon Dec 11 11:53:57 PST 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxxabi
@llvm/pr-subscribers-libcxx
Author: Louis Dionne (ldionne)
<details>
<summary>Changes</summary>
When we use the -nostdlib++ flag, we don't need to explicitly link against compiler-rt, since the compiler already links against it by default. This simplifies the flags that we need to use when building with Clang and GCC, and opens the door to further simplifications since most platforms won't need to detect whether libgcc and libgcc_s are supported anymore.
Furthermore, on platforms where -nostdlib++ is used, this patch prevents manually linking compiler-rt *before* other system libraries. For example, Apple platforms have several compiler-rt symbols defined in libSystem.dylib. If we manually link against compiler-rt, we end up overriding the default link order preferred by the compiler and potentially using the symbols from the clang-provided libclang_rt.a library instead of the system provided one.
Note that we don't touch how libunwind links against compiler-rt when it builds the .so/.a because libunwind currently doesn't use -nodefaultlibs and we want to avoid rocking the boat too much.
rdar://119506163
---
Full diff: https://github.com/llvm/llvm-project/pull/75089.diff
5 Files Affected:
- (modified) libcxx/CMakeLists.txt (+10-8)
- (modified) libcxx/cmake/config-ix.cmake (+6-1)
- (modified) libcxxabi/cmake/config-ix.cmake (+6-1)
- (modified) libcxxabi/src/CMakeLists.txt (+4-1)
- (modified) libunwind/cmake/config-ix.cmake (+6-1)
``````````diff
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 31fc9cec1c57f..2a1458a098d2e 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -655,15 +655,17 @@ function(cxx_link_system_libraries target)
target_add_link_flags_if_supported(${target} PRIVATE "--unwindlib=none")
endif()
- if (LIBCXX_USE_COMPILER_RT)
- find_compiler_rt_library(builtins LIBCXX_BUILTINS_LIBRARY)
- if (LIBCXX_BUILTINS_LIBRARY)
- target_link_libraries(${target} PRIVATE "${LIBCXX_BUILTINS_LIBRARY}")
+ if (MSVC)
+ if (LIBCXX_USE_COMPILER_RT)
+ find_compiler_rt_library(builtins LIBCXX_BUILTINS_LIBRARY)
+ if (LIBCXX_BUILTINS_LIBRARY)
+ target_link_libraries(${target} PRIVATE "${LIBCXX_BUILTINS_LIBRARY}")
+ endif()
+ elseif (LIBCXX_HAS_GCC_LIB)
+ target_link_libraries(${target} PRIVATE gcc)
+ elseif (LIBCXX_HAS_GCC_S_LIB)
+ target_link_libraries(${target} PRIVATE gcc_s)
endif()
- elseif (LIBCXX_HAS_GCC_LIB)
- target_link_libraries(${target} PRIVATE gcc)
- elseif (LIBCXX_HAS_GCC_S_LIB)
- target_link_libraries(${target} PRIVATE gcc_s)
endif()
if (LIBCXX_HAS_ATOMIC_LIB)
diff --git a/libcxx/cmake/config-ix.cmake b/libcxx/cmake/config-ix.cmake
index a365517936e75..1e8c2f5ce4632 100644
--- a/libcxx/cmake/config-ix.cmake
+++ b/libcxx/cmake/config-ix.cmake
@@ -45,7 +45,9 @@ else()
endif()
endif()
-if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
+# Only link against compiler-rt manually if we use -nodefaultlibs, since
+# otherwise the compiler will do the right thing on its own.
+if (NOT CXX_SUPPORTS_NOSTDLIBXX_FLAG AND C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (LIBCXX_USE_COMPILER_RT)
include(HandleCompilerRT)
find_compiler_rt_library(builtins LIBCXX_BUILTINS_LIBRARY
@@ -73,6 +75,9 @@ if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
moldname mingwex msvcrt)
list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
endif()
+endif()
+
+if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
endif ()
diff --git a/libcxxabi/cmake/config-ix.cmake b/libcxxabi/cmake/config-ix.cmake
index 39b9284b780eb..10f2087c68c5e 100644
--- a/libcxxabi/cmake/config-ix.cmake
+++ b/libcxxabi/cmake/config-ix.cmake
@@ -33,7 +33,9 @@ else()
endif()
endif()
-if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
+# Only link against compiler-rt manually if we use -nodefaultlibs, since
+# otherwise the compiler will do the right thing on its own.
+if (NOT CXX_SUPPORTS_NOSTDLIBXX_FLAG AND C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (LIBCXXABI_HAS_C_LIB)
list(APPEND CMAKE_REQUIRED_LIBRARIES c)
endif ()
@@ -67,6 +69,9 @@ if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
moldname mingwex msvcrt)
list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
endif()
+endif()
+
+if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
endif ()
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 02031b69fd915..4198827203fc8 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -166,7 +166,10 @@ if (LIBCXXABI_USE_LLVM_UNWINDER)
target_link_libraries(cxxabi_shared_objects PUBLIC unwind_shared)
endif()
endif()
-target_link_libraries(cxxabi_shared_objects PRIVATE cxx-headers ${LIBCXXABI_BUILTINS_LIBRARY} ${LIBCXXABI_LIBRARIES})
+target_link_libraries(cxxabi_shared_objects PRIVATE cxx-headers ${LIBCXXABI_LIBRARIES})
+if (NOT CXX_SUPPORTS_NOSTDLIBXX_FLAG)
+ target_link_libraries(cxxabi_shared_objects PRIVATE ${LIBCXXABI_BUILTINS_LIBRARY})
+endif()
target_link_libraries(cxxabi_shared_objects PUBLIC cxxabi-headers)
set_target_properties(cxxabi_shared_objects
PROPERTIES
diff --git a/libunwind/cmake/config-ix.cmake b/libunwind/cmake/config-ix.cmake
index 7df8974b0a925..126c872f0d489 100644
--- a/libunwind/cmake/config-ix.cmake
+++ b/libunwind/cmake/config-ix.cmake
@@ -45,7 +45,9 @@ else()
endif()
endif()
-if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
+# Only link against compiler-rt manually if we use -nodefaultlibs, since
+# otherwise the compiler will do the right thing on its own.
+if (NOT CXX_SUPPORTS_NOSTDLIBXX_FLAG AND C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (LIBUNWIND_HAS_C_LIB)
list(APPEND CMAKE_REQUIRED_LIBRARIES c)
endif ()
@@ -78,6 +80,9 @@ if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
moldname mingwex msvcrt)
list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
endif()
+endif()
+
+if (CXX_SUPPORTS_NOSTDLIBXX_FLAG OR C_SUPPORTS_NODEFAULTLIBS_FLAG)
if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
endif ()
``````````
</details>
https://github.com/llvm/llvm-project/pull/75089
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