[libcxx] Specify unwind lib before other system libraries.

[ychen]

Summary

For the same reason as D57496. This and D57496 combined make local unwind lib
picked up by dyld in a libcxx/libcxxabi/libunwind build on OSX.

before
➜ libcxx otool -L lib/libc++.dylib
lib/libc++.dylib:

@rpath/libc++.1.dylib (compatibility version 1.0.0, current version 1.0.0)
@rpath/libc++abi.1.dylib (compatibility version 1.0.0, current version 1.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1252.200.5)
@rpath/libunwind.1.dylib (compatibility version 1.0.0, current version 1.0.0)

to
➜ libcxx otool -L lib/libc++.dylib
lib/libc++.dylib:

@rpath/libc++.1.dylib (compatibility version 1.0.0, current version 1.0.0)
@rpath/libc++abi.1.dylib (compatibility version 1.0.0, current version 1.0.0)
@rpath/libunwind.1.dylib (compatibility version 1.0.0, current version 1.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1252.200.5)

[ychen]

• update

[phosek]

LGTM

[ychen]

Could you please commit this for me? Thanks.

[ldionne]

@phosek Has this been committed?

[phosek]

Not yet, but it'll probably need to be reworked given all the changes that landed in libc++.

[ychen]

rebase

[ldionne]

I'll admit that I find it very brittle that ordering matters. We can do this, however it would be better to find another solution that doesn't require depending on the ordering of -l parameters. I don't know what that would be, though.

[ychen]

In D57646#1490180, @ldionne wrote:

I'll admit that I find it very brittle that ordering matters. We can do this, however it would be better to find another solution that doesn't require depending on the ordering of -l parameters. I don't know what that would be, though.

install_name_tool -change could adjust the order for executable as a post build action. If there are additional dependent libraries, then reorder logic need to be updated. I'm not sure it would be an improvement than just put more comments in the existing code since overriding libSystem.B.dylib is a rare case.

[ldionne]

In D57646#1490202, @tabloid.adroit wrote:

In D57646#1490180, @ldionne wrote:

I'll admit that I find it very brittle that ordering matters. We can do this, however it would be better to find another solution that doesn't require depending on the ordering of -l parameters. I don't know what that would be, though.

install_name_tool -change could adjust the order for executable as a post build action. If there are additional dependent libraries, then reorder logic need to be updated. I'm not sure it would be an improvement than just put more comments in the existing code since overriding libSystem.B.dylib is a rare case.

innstall_name_tool is only available on Darwin unless I'm mistaken, so I think it's better not to add something that only works on a specific platform. It's an interesting suggestion nonetheless.

[ychen]

• add comment

[ychen]

Hi ldionne, I definitely agree install_name_tool is not a desired solution. I've also added some comments so people realize the issue when modifying the code.

[ychen]

ping.

[ldionne]

[Github PR transition cleanup]

Abandoning since this will be solved by https://github.com/llvm/llvm-project/pull/66940.

lib/CMakeLists.txt

 if(NOT LIBCXX_INSTALL_LIBRARY)
   set(exclude_from_all EXCLUDE_FROM_ALL)
 endif()
 
 # If LIBCXX_CXX_ABI_LIBRARY_PATH is defined we want to add it to the search path.
 add_link_flags_if(LIBCXX_CXX_ABI_LIBRARY_PATH
                   "${CMAKE_LIBRARY_PATH_FLAG}${LIBCXX_CXX_ABI_LIBRARY_PATH}")
 
-
 if (LIBCXX_GENERATE_COVERAGE AND NOT LIBCXX_COVERAGE_LIBRARY)
   find_compiler_rt_library(profile LIBCXX_COVERAGE_LIBRARY)
 endif()
 add_library_flags_if(LIBCXX_COVERAGE_LIBRARY "${LIBCXX_COVERAGE_LIBRARY}")
 
 if (APPLE AND (LIBCXX_CXX_ABI_LIBNAME STREQUAL "libcxxabi" OR
                LIBCXX_CXX_ABI_LIBNAME STREQUAL "default"))
   set(LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS ON)
if (LIBFILE)
     set(LIBCXX_SANITIZER_LIBRARY "${LIBDIR}/${LIBFILE}")
     set(LIBCXX_SANITIZER_LIBRARY "${LIBCXX_SANITIZER_LIBRARY}" PARENT_SCOPE)
     message(STATUS "Manually linking compiler-rt library: ${LIBCXX_SANITIZER_LIBRARY}")
     add_library_flags("${LIBCXX_SANITIZER_LIBRARY}")
     add_link_flags("-Wl,-rpath,${LIBDIR}")
   endif()
 endif()
 
+# Add the unwinder library.
+if (LIBCXXABI_USE_LLVM_UNWINDER)
+  if (NOT LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
+    add_interface_library(unwind_shared)
+  elseif (LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_static OR HAVE_LIBUNWIND))
+    add_interface_library(unwind_static)
+  else()
+    add_interface_library(unwind)
+  endif()
+endif()
+
 # Generate private library list.
 add_library_flags_if(LIBCXX_HAS_PTHREAD_LIB pthread)
 add_library_flags_if(LIBCXX_HAS_C_LIB c)
 add_library_flags_if(LIBCXX_HAS_M_LIB m)
 add_library_flags_if(LIBCXX_HAS_RT_LIB rt)
 if (LIBCXX_USE_COMPILER_RT)
   find_compiler_rt_library(builtins LIBCXX_BUILTINS_LIBRARY)
   add_library_flags_if(LIBCXX_BUILTINS_LIBRARY "${LIBCXX_BUILTINS_LIBRARY}")
 else()
   add_library_flags_if(LIBCXX_HAS_GCC_S_LIB gcc_s)
 endif()
 add_library_flags_if(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB atomic)
 add_library_flags_if(MINGW "${MINGW_LIBRARIES}")
 
-# Add the unwinder library.
-if (LIBCXXABI_USE_LLVM_UNWINDER)
-  if (NOT LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
-    add_interface_library(unwind_shared)
-  elseif (LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_static OR HAVE_LIBUNWIND))
-    add_interface_library(unwind_static)
-  else()
-    add_interface_library(unwind)
-  endif()
-endif()
-
 # Setup flags.
 if (NOT WIN32)
   add_flags_if_supported(-fPIC)
 endif()
 
 add_link_flags_if_supported(-nodefaultlibs)
 
 if (LIBCXX_TARGETING_MSVC)