MSYS2: Export forwarders for __cxa_begin_catch, __cxa_end_catch, __cxa_rethrow and __gxx_personality_seh0
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…`__cxa_rethrow` and `__gxx_personality_seh0` libobjc2 uses native C++ exceptions on MinGW. The clang compiler will emit references to `__cxa_begin_catch`, `__cxa_end_catch`, `__cxa_rethrow` and `__gxx_personality_seh0` for Objective C code which uses Objective C exceptions. These symbols are defined in the C++ runtime, not in libobjc2. As a result, merely linking with libobjc2 is not sufficient. Objective C code such as GNUstep must be compiled with the `LDFLAGS="-lgcc_s -lstdc++"` or `LDFLAGS="-lc++"`, depending on the environment. This is tedious. Additionally, specifying `-lc++` on the msys/clang64 environment causes linker errors: ``` Linking library libgnustep-base ... ld.lld: error: libc++.dll.a(libc++.dll): .idata$4 should not refer to special section 0 ``` A [similar error has been observed for other libraries](msys2/MINGW-packages#18589) A solution for this is to define forwarding exports for `__cxa_begin_catch`, `__cxa_end_catch`, `__cxa_rethrow` and `__gxx_personality_seh0`. This is implemented by adding a `eh_forwards.def` file to the list of libobjc2 source files, which forwards the symbols to the actual C++ runtime. On MSYS2, the libstdc++ and libc++ runtimes are supported, which covers all MinGW environments: https://www.msys2.org/docs/environments/. Forwarding exports are discussed here: - https://learn.microsoft.com/en-us/cpp/build/reference/exports?view=msvc-170 - https://devblogs.microsoft.com/oldnewthing/20060719-24/?p=30473 - https://devblogs.microsoft.com/oldnewthing/20121116-00/?p=6073
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libobjc2 uses native C++ exceptions on MinGW. The clang compiler will emit references to
__cxa_begin_catch,__cxa_end_catch,__cxa_rethrowand__gxx_personality_seh0for Objective C code which uses Objective C exceptions.These symbols are defined in the C++ runtime, not in libobjc2. As a result, merely linking with libobjc2 is not sufficient. Objective C code such as GNUstep must be compiled with the
LDFLAGS="-lgcc_s -lstdc++"orLDFLAGS="-lc++", depending on the environment.This is tedious. Additionally, specifying
-lc++on the msys/clang64 environment causes linker errors:A similar error has been observed for other libraries
A solution for this is to define forwarding exports for
__cxa_begin_catch,__cxa_end_catch,__cxa_rethrowand__gxx_personality_seh0. This is implemented by adding aeh_forwards.deffile to the list of libobjc2 source files, which forwards the symbols to the actual C++ runtime. On MSYS2, the libstdc++ and libc++ runtimes are supported, which covers all MinGW environments: https://www.msys2.org/docs/environments/.Forwarding exports are discussed here: