How to set LIBCXX variables in a bootstrapping build of libc++?

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(Sorry for the amount of topics lately. I figured it’s better than asking on Discord since posting here at least gives everyone a chance to benefit from the discussions.)

When setting LIBCXX variables in a default build of libc++ (-S runtimes), they are used by CMake. However, the same is not true for bootstrapping builds (-S llvm), unless I’m doing something wrong:

$ cmake -DCMAKE_BUILD_TYPE=Release -DLIBCXX_ENABLE_SHARED=OFF -DLLVM_ENABLE_RUNTIMES=libcxx -LAH -B build -S llvm | grep LIBCXX_ENABLE_SHARED
# nothing
$ cmake -DCMAKE_BUILD_TYPE=Release -DLIBCXX_ENABLE_SHARED=OFF -DLLVM_ENABLE_RUNTIMES=libcxx -LAH -B build -S runtimes | grep LIBCXX_ENABLE_SHARED
LIBCXX_ENABLE_SHARED:BOOL=OFF

This is reflected when actually building: The default build disables the shared library, while the bootstrapping one does not.

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Sorry I don’t have the solution but is this these open issues?

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Yeah, that sounds like it. We’ll need to wait for the developers to see it then. Thanks!

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cmake variables are not propagated as is into the runtimes build by design.

You are supposed to prefix them with RUNTIMES_<target-triple>_ if you want to forward them.

For example, -DRUNTIMES_<target-triple>_LIBCXX_ENABLE_SHARED=OFF should work.

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