https://github.com/ldionne created
https://github.com/llvm/llvm-project/pull/75089
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
>From 60950d80acb9364a5e4bc87dd496f80693e28b2a Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionn...@gmail.com>
Date: Mon, 11 Dec 2023 14:17:26 -0500
Subject: [PATCH] [runtimes] Don't link against compiler-rt explicitly when we
use -nostdlib++
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
---
libcxx/CMakeLists.txt | 18 ++++++++++--------
libcxx/cmake/config-ix.cmake | 7 ++++++-
libcxxabi/cmake/config-ix.cmake | 7 ++++++-
libcxxabi/src/CMakeLists.txt | 5 ++++-
libunwind/cmake/config-ix.cmake | 7 ++++++-
5 files changed, 32 insertions(+), 12 deletions(-)
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 31fc9cec1c57f2..2a1458a098d2e7 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 a365517936e756..1e8c2f5ce46321 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 39b9284b780ebc..10f2087c68c5e7 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 02031b69fd9156..4198827203fc8b 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 7df8974b0a9254..126c872f0d4895 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 ()
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