[libunwind] [runtimes] Fix link order of system librarires on Apple platforms (PR #66940)
via cfe-commits
cfe-commits at lists.llvm.org
Wed Sep 20 11:46:10 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
<details>
<summary>Changes</summary>
On Apple platforms, we always support the -nostdlib++ flag. Hence, it is not necessary to manually link against system libraries. In fact, doing so causes us to link against libSystem explicitly, which messes up with the order of libraries we should use. Indeed:
```
Before patch, using the system unwinder (LIBCXXABI_USE_LLVM_UNWINDER = OFF)
===========================================================================
$ otool -L lib/{libc++.1.dylib,libc++abi.1.dylib,libunwind.1.dylib}
lib/libc++.1.dylib:
@<!-- -->rpath/libc++.1.dylib
/usr/lib/libSystem.B.dylib
@<!-- -->rpath/libc++abi.1.dylib
lib/libc++abi.1.dylib:
@<!-- -->rpath/libc++abi.1.dylib
/usr/lib/libSystem.B.dylib
lib/libunwind.1.dylib:
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
After patch, using the system unwinder (LIBCXXABI_USE_LLVM_UNWINDER = OFF)
===========================================================================
$ otool -L lib/{libc++.1.dylib,libc++abi.1.dylib,libunwind.1.dylib}
lib/libc++.1.dylib:
@<!-- -->rpath/libc++.1.dylib
@<!-- -->rpath/libc++abi.1.dylib
/usr/lib/libSystem.B.dylib
lib/libc++abi.1.dylib:
@<!-- -->rpath/libc++abi.1.dylib
/usr/lib/libSystem.B.dylib
lib/libunwind.1.dylib:
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
Before patch, with the LLVM unwinder (LIBCXXABI_USE_LLVM_UNWINDER = ON)
=======================================================================
$ otool -L lib/{libc++.1.dylib,libc++abi.1.dylib,libunwind.1.dylib}
lib/libc++.1.dylib:
@<!-- -->rpath/libc++.1.dylib
/usr/lib/libSystem.B.dylib
@<!-- -->rpath/libc++abi.1.dylib
@<!-- -->rpath/libunwind.1.dylib
lib/libc++abi.1.dylib:
@<!-- -->rpath/libc++abi.1.dylib
/usr/lib/libSystem.B.dylib
@<!-- -->rpath/libunwind.1.dylib
lib/libunwind.1.dylib:
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
After patch, with the LLVM unwinder (LIBCXXABI_USE_LLVM_UNWINDER = ON)
======================================================================
$ otool -L lib/{libc++.1.dylib,libc++abi.1.dylib,libunwind.1.dylib}
lib/libc++.1.dylib:
@<!-- -->rpath/libc++.1.dylib
@<!-- -->rpath/libc++abi.1.dylib
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
lib/libc++abi.1.dylib:
@<!-- -->rpath/libc++abi.1.dylib
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
lib/libunwind.1.dylib:
@<!-- -->rpath/libunwind.1.dylib
/usr/lib/libSystem.B.dylib
```
As we can see, libSystem appears before the just-built libraries before the patch, which causes the libunwind.dylib bundled in libSystem.dylib to be used instead of the just-built libunwind.dylib.
We didn't notice the issue until recently when I tried to update the macOS CI builders to macOS 13.5, where it is necessary to use the right libunwind library (the exact reason still needs to be investigated).
---
Full diff: https://github.com/llvm/llvm-project/pull/66940.diff
5 Files Affected:
- (modified) libcxx/CMakeLists.txt (+13-15)
- (modified) libcxx/cmake/config-ix.cmake (-4)
- (modified) libcxxabi/cmake/config-ix.cmake (-2)
- (modified) libcxxabi/src/CMakeLists.txt (+1-3)
- (modified) libunwind/src/CMakeLists.txt (+10-3)
``````````diff
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index bb2898b799bcef9..68410feb9661816 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -659,24 +659,22 @@ function(cxx_link_system_libraries target)
target_add_link_flags_if_supported(${target} PRIVATE "--unwindlib=none")
endif()
- if (LIBCXX_HAS_SYSTEM_LIB)
- target_link_libraries(${target} PRIVATE System)
- endif()
-
- if (LIBCXX_HAS_PTHREAD_LIB)
- target_link_libraries(${target} PRIVATE pthread)
- endif()
+ if (NOT APPLE) # On Apple platforms, we always use -nostdlib++ so we don't need to re-add other libraries
+ if (LIBCXX_HAS_PTHREAD_LIB)
+ target_link_libraries(${target} PRIVATE pthread)
+ endif()
- if (LIBCXX_HAS_C_LIB)
- target_link_libraries(${target} PRIVATE c)
- endif()
+ if (LIBCXX_HAS_C_LIB)
+ target_link_libraries(${target} PRIVATE c)
+ endif()
- if (LIBCXX_HAS_M_LIB)
- target_link_libraries(${target} PRIVATE m)
- endif()
+ if (LIBCXX_HAS_M_LIB)
+ target_link_libraries(${target} PRIVATE m)
+ endif()
- if (LIBCXX_HAS_RT_LIB)
- target_link_libraries(${target} PRIVATE rt)
+ if (LIBCXX_HAS_RT_LIB)
+ target_link_libraries(${target} PRIVATE rt)
+ endif()
endif()
if (LIBCXX_USE_COMPILER_RT)
diff --git a/libcxx/cmake/config-ix.cmake b/libcxx/cmake/config-ix.cmake
index 3bae53643683581..9962d848d85e846 100644
--- a/libcxx/cmake/config-ix.cmake
+++ b/libcxx/cmake/config-ix.cmake
@@ -110,10 +110,8 @@ if(WIN32 AND NOT MINGW)
set(LIBCXX_HAS_PTHREAD_LIB NO)
set(LIBCXX_HAS_M_LIB NO)
set(LIBCXX_HAS_RT_LIB NO)
- set(LIBCXX_HAS_SYSTEM_LIB NO)
set(LIBCXX_HAS_ATOMIC_LIB NO)
elseif(APPLE)
- check_library_exists(System write "" LIBCXX_HAS_SYSTEM_LIB)
set(LIBCXX_HAS_PTHREAD_LIB NO)
set(LIBCXX_HAS_M_LIB NO)
set(LIBCXX_HAS_RT_LIB NO)
@@ -122,12 +120,10 @@ elseif(FUCHSIA)
set(LIBCXX_HAS_M_LIB NO)
set(LIBCXX_HAS_PTHREAD_LIB NO)
set(LIBCXX_HAS_RT_LIB NO)
- set(LIBCXX_HAS_SYSTEM_LIB NO)
check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
else()
check_library_exists(pthread pthread_create "" LIBCXX_HAS_PTHREAD_LIB)
check_library_exists(m ccos "" LIBCXX_HAS_M_LIB)
check_library_exists(rt clock_gettime "" LIBCXX_HAS_RT_LIB)
- set(LIBCXX_HAS_SYSTEM_LIB NO)
check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
endif()
diff --git a/libcxxabi/cmake/config-ix.cmake b/libcxxabi/cmake/config-ix.cmake
index f4ee8946c1fea41..702fe7d1d72f777 100644
--- a/libcxxabi/cmake/config-ix.cmake
+++ b/libcxxabi/cmake/config-ix.cmake
@@ -95,11 +95,9 @@ if(FUCHSIA)
set(LIBCXXABI_HAS_PTHREAD_LIB NO)
check_library_exists(c __cxa_thread_atexit_impl ""
LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)
- set(LIBCXXABI_HAS_SYSTEM_LIB NO)
else()
check_library_exists(dl dladdr "" LIBCXXABI_HAS_DL_LIB)
check_library_exists(pthread pthread_once "" LIBCXXABI_HAS_PTHREAD_LIB)
check_library_exists(c __cxa_thread_atexit_impl ""
LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)
- check_library_exists(System write "" LIBCXXABI_HAS_SYSTEM_LIB)
endif()
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 3ad755803ac9c87..a3a73620bd9ff78 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -67,9 +67,7 @@ if (LIBCXXABI_ENABLE_FORGIVING_DYNAMIC_CAST)
add_definitions(-D_LIBCXXABI_FORGIVING_DYNAMIC_CAST)
endif()
-if (APPLE)
- add_library_flags_if(LIBCXXABI_HAS_SYSTEM_LIB System)
-else()
+if (NOT APPLE) # On Apple platforms, we always use -nostdlib++ so we don't need to re-add other libraries
if (LIBCXXABI_ENABLE_THREADS)
add_library_flags_if(LIBCXXABI_HAS_PTHREAD_LIB pthread)
endif()
diff --git a/libunwind/src/CMakeLists.txt b/libunwind/src/CMakeLists.txt
index a9bf29a8b394a4c..452d988c3726b5e 100644
--- a/libunwind/src/CMakeLists.txt
+++ b/libunwind/src/CMakeLists.txt
@@ -65,16 +65,23 @@ set(LIBUNWIND_SOURCES
${LIBUNWIND_ASM_SOURCES})
# Generate library list.
-add_library_flags_if(LIBUNWIND_HAS_C_LIB c)
if (LIBUNWIND_USE_COMPILER_RT)
add_library_flags("${LIBUNWIND_BUILTINS_LIBRARY}")
else()
add_library_flags_if(LIBUNWIND_HAS_GCC_S_LIB gcc_s)
add_library_flags_if(LIBUNWIND_HAS_GCC_LIB gcc)
endif()
-add_library_flags_if(LIBUNWIND_HAS_DL_LIB dl)
+if (NOT APPLE) # On Apple platforms, we don't need to link explicitly against system libraries
+ add_library_flags_if(LIBUNWIND_HAS_C_LIB c)
+ add_library_flags_if(LIBUNWIND_HAS_DL_LIB dl)
+
+ if (LIBUNWIND_ENABLE_THREADS)
+ add_library_flags_if(LIBUNWIND_HAS_PTHREAD_LIB pthread)
+ add_compile_flags_if(LIBUNWIND_WEAK_PTHREAD_LIB -DLIBUNWIND_USE_WEAK_PTHREAD=1)
+ endif()
+endif()
+
if (LIBUNWIND_ENABLE_THREADS)
- add_library_flags_if(LIBUNWIND_HAS_PTHREAD_LIB pthread)
add_compile_flags_if(LIBUNWIND_WEAK_PTHREAD_LIB -DLIBUNWIND_USE_WEAK_PTHREAD=1)
endif()
``````````
</details>
https://github.com/llvm/llvm-project/pull/66940
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