[libcxx-dev] [llvm-dev] Shipping custom libc++ on MacOS

[Louis Dionne via libcxx-dev]

> On Jul 10, 2021, at 09:33, Isuru Fernando via libcxx-dev <libcxx-dev at lists.llvm.org> wrote:
> 
> Hi Ken,
> 
> I'm in the same situation as you in conda package manager.
> Note that with libcxx 12, https://reviews.llvm.org/D91517 <https://reviews.llvm.org/D91517> was merged where
> codecvt with char8_t is added in the middle of a structure instead of at the end.
> This means that you have to be careful that all applications link to the custom libc++.
> 
> For libcxx developers,
> While we are discussing how to avoid ODR violations, is it possible to move the two lines at
> https://github.com/llvm/llvm-project/blob/llvmorg-12.0.1/libcxx/src/locale.cpp#L210-L211  <https://github.com/llvm/llvm-project/blob/llvmorg-12.0.1/libcxx/src/locale.cpp#L210-L211>
> to the bottom to avoid segfaults resulting from this?

Generally speaking, we make the assumption that there's a single copy of libc++ in use inside a final linked image. Or if you want to use libc++ as an implementation detail and link it statically, ensure it doesn't export any symbols and has absolutely no ABI surface outside of the executable where it's being used. Chrome does that.

Anything else is very brittle, and I'm reluctant to add workarounds that make it look like it works, because you may run into other issues that we won't be able to patch so easily.

Louis

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