[llvm-dev] cmake 3.22 breaks libc++ build

[PoYao Chang via llvm-dev]

I ran in to this exact problem (cmake trying to modify rpath of a linker script) too.
The workaround I employed was setting “LIBCXX_ENABLE_STATIC_ABI_LIBRARY” to ON.
Works on 13.0.0 and ToT. 
Hope this helps.

> On Dec 3, 2021, at 6:28 PM, Roland Schatz via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> I'm currently debugging a problem in our Github Actions build. We're doing a custom build of libc++ and libc++abi, and this is failing since the cmake version in the base image was updated to version 3.22.
> 
> The issue can be reproduced by following the instructions at https://libcxx.llvm.org/BuildingLibcxx.html <https://libcxx.llvm.org/BuildingLibcxx.html>.
> 
> The setup I'm using is this:
> * Linux
> * cmake version 3.22
> * I've tried llvm-project sources 12.0.0, 13.0.0 and the tip of main
> * system compiler is clang 12.0.1 (but I don't think that matters here)
> 
> The exact commands I'm running are (the last one is failing [1]):
> cd llvm-project
> mkdir build
> cmake -G Ninja -S runtimes -B build "-DLLVM_ENABLE_RUNTIMES=libcxx;libcxxabi"           -DCMAKE_INSTALL_PREFIX=install
> ninja -C build cxx cxxabi
> ninja -C build install-cxxabi
> ninja -C build install-cxx
> 
> 
> What seems to be happening is that cmake tries to patch the RPATH of libc++.so. But libc++.so is not a symlink to a shared object, it's a linker script.
> I have bisected that to a particular cmake change [2].
> 
> 
> One thing I noticed is that the build works just fine when I'm doing the build of libc++ and libc++abi separately:
> 
> cmake -S libcxxabi ...
> // build, install, ...
> cmake -S libcxx -DLIBCXX_CXX_ABI=libcxxabi -DLIBCXX_CXX_ABI_LIBRARY_PATH=path/to/install/from/prev/step ...
> 
> That works on Linux, but breaks the build on Darwin, it seems to be missing the re-exports of libc++abi symbols in libc++ then.
> Also that's the "deprecated" way of doing things, so not sure if it's good to pursue that path.
> 
> 
> To be honest, I'm not sure I fully understand the problem, or how these different ways of building even make a difference.
> 
> Am I doing something wrong? Is this a bug in LLVM's cmake scripts? Or a bug in cmake?
> Any hints what I can try to fix this?
> 
> 
> Thanks!
> Roland
> 
> 
> [1] failing build output:
> 
> ...
> -- Installing: /home/roland/test/cmake/llvm-project/install/include/c++/v1/wctype.h
> -- Installing: /home/roland/test/cmake/llvm-project/install/include/c++/v1/__config_site
> [4/4] cd /home/roland/test/cmake/llvm-project/build/libcxx/src && /nix/store/n7j...ENT=cxx -P /home/roland/test/cmake/llvm-project/build/libcxx/cmake_install.cmake
> FAILED: libcxx/src/CMakeFiles/install-cxx /home/roland/test/cmake/llvm-project/build/libcxx/src/CMakeFiles/install-cxx
> cd /home/roland/test/cmake/llvm-project/build/libcxx/src && /nix/store/n7jz18i0cspdkfd1y0w1mg5rqvs15kdr-cmake-3.22.0/bin/cmake -DCMAKE_INSTALL_COMPONENT=cxx -P /home/roland/test/cmake/llvm-project/build/libcxx/cmake_install.cmake
> -- Install configuration: ""
> -- Installing: /home/roland/test/cmake/llvm-project/install/lib/libc++.so.1.0
> -- Installing: /home/roland/test/cmake/llvm-project/install/lib/libc++.so.1
> -- Set runtime path of "/home/roland/test/cmake/llvm-project/install/lib/libc++.so.1.0" to ""
> -- Installing: /home/roland/test/cmake/llvm-project/install/lib/libc++.so
> CMake Error at cmake_install.cmake:88 (file):
>   file RPATH_CHANGE could not write new RPATH:
> 
> 
> 
>   to the file:
> 
>     /home/roland/test/cmake/llvm-project/install/lib/libc++.so
> 
> Call Stack (most recent call first):
>   /home/roland/test/cmake/llvm-project/build/libcxx/cmake_install.cmake:56 (include)
> 
> 
> ninja: build stopped: subcommand failed.
> 
> [2] https://github.com/Kitware/CMake/commit/2e1149874d34b63cc16c7330ce1ef5ef779e5140 <https://github.com/Kitware/CMake/commit/2e1149874d34b63cc16c7330ce1ef5ef779e5140>
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