[libcxx-commits] [libcxx] 61e8973 - [libc++] Simplify the configuration of the C++ ABI library

[Nico Weber via libcxx-commits]

…see discussion on the bug that Louis linked to :)

On Thu, Apr 2, 2020 at 2:34 PM Shoaib Meenai via libcxx-commits <
libcxx-commits at lists.llvm.org> wrote:

> Can you just build the cxx-headers target instead of doing a full libc++
> build? That's what we do for some of our builds which have a similar issue
> with requiring the headers.
>
> On 4/2/20, 9:54 AM, "libcxx-commits on behalf of Hans Wennborg via
> libcxx-commits" <libcxx-commits-bounces at lists.llvm.org on behalf of
> libcxx-commits at lists.llvm.org> wrote:
>
>     On Thu, Apr 2, 2020 at 8:21 AM Louis Dionne via libcxx-commits
>     <libcxx-commits at lists.llvm.org> wrote:
>     >
>     >
>     > Author: Louis Dionne
>     > Date: 2020-04-02T02:21:15-04:00
>     > New Revision: 61e89737c5daf7b65341936f88f68efb680cdcd4
>     >
>     > URL:
> https://github.com/llvm/llvm-project/commit/61e89737c5daf7b65341936f88f68efb680cdcd4
>     > DIFF:
> https://github.com/llvm/llvm-project/commit/61e89737c5daf7b65341936f88f68efb680cdcd4.diff
>     >
>     > LOG: [libc++] Simplify the configuration of the C++ ABI library
>     >
>     > This commit removes support for building against the system
> libc++abi,
>     > which was supported on Apple platforms. This is basically never what
> we
>     > want to do, since libc++ and libc++abi are coupled and building a
> trunk
>     > libc++ against an older libc++abi can lead to incompatibilities (and
>     > good luck debugging them!). It might have made some sense to support
>     > that when the monorepo did not exist, however I don't think this is
>     > anything but a footgun nowadays.
>     >
>     > Furthermore, based on the newly-made assumption that we're building
>     > against the monorepo libc++abi, we can simplify the search path logic
>     > for finding libc++abi.
>     >
>     > This area of our build system has a lot of technical debt
> accumulated,
>     > and it's surprisingly difficult to change. We've tried different
> things
>     > and failed several times in the past. I did test this change on our
>     > Docker image for the build bots and on Apple platforms, however it is
>     > possible that this breaks some unknown configuration, in which case
> it
>     > should be fine to revert this (so we can try again!).
>
>     Well hello :-)
>
>     This broke Chromium's packaging of Clang on Mac (see
> https://urldefense.proofpoint.com/v2/url?u=https-3A__crbug.com_1067216&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=SWiE-LfJQGnDioVJ_1oMe3PytSX5eiUvQpefAQsuazY&s=lE5OJxnVAVB3rbcM6cb6l_98rAS88IWoGG10qGpGhdA&e=
> ).
>
>     We build libc++ as part of that process, not because we ship it with
>     the compiler, but as part of the bootstrapping process: otherwise the
>     just-built Clang doesn't find the c++ headers. Until now we've been
>     building with -DLIBCXX_CXX_ABI=libcxxabi -DLIBCXX_CXX_ABI_SYSTEM=1
>     however with your patch that stopped working.
>
>     I tried adding libcxxabi to -DLLVM_ENABLE_PROJECTS and dropping those
>     two flags, but now building libcxxabi failed for unclear reasons
>     ([1]).
>
>     Would it be okay to revert your patch until we've figured this out?
>
>     Thanks,
>     Hans
>
>      1.
> https://urldefense.proofpoint.com/v2/url?u=https-3A__logs.chromium.org_logs_chromium_buildbucket_cr-2Dbuildbucket.appspot.com_8884121514869999920_-2B_steps_package-5Fclang_0_stdout&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=SWiE-LfJQGnDioVJ_1oMe3PytSX5eiUvQpefAQsuazY&s=sjaVvsQRbGGGSN4z6WyYuXoG8V1t706w716SXjj6TKw&e=
>     _______________________________________________
>     libcxx-commits mailing list
>     libcxx-commits at lists.llvm.org
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_libcxx-2Dcommits&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=SWiE-LfJQGnDioVJ_1oMe3PytSX5eiUvQpefAQsuazY&s=00dVbLac1W5uZANZvwp36madK749LqVwkoD3LhxoVNo&e=
>
>
> _______________________________________________
> libcxx-commits mailing list
> libcxx-commits at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/libcxx-commits/attachments/20200402/9e0a2555/attachment.html>