llvm dev - Dec 2016 - Bootstrapping with in-tree libcxx

When I tried to build with -DLLVM_ENABLE_LIBCXX, I found out that
it doesn't try to use the in-tree libcxx but looks for one built and
installed
in the system.

Since building all of llvm required CXX and using libcxx with the same
version as the rest of llvm makes sense, I would certainly appreciate
an option to build the in-tree libcxx as a first step and use it in when
building llvm, lld, lldb, clang, ...

Since llvm already builds many other DSOs it needs at runtime, adding
libcxx is reasonable. More so if we consider that not all systems package
libcxx at the same version as clang and llvm. For instance, Arch Linux
has libcxx 3.8.0 but llvm and clang 3.9.0.

On Tue, Dec 27, 2016 at 1:29 PM, Carsten Mattner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> When I tried to build with -DLLVM_ENABLE_LIBCXX, I found out that
> it doesn't try to use the in-tree libcxx but looks for one built and
> installed
> in the system.
>
IIRC, -DLLVM_ENABLE_LIBCXX reduces to passing --stdlib=libc++ (see [1]) to
the compiler.

What you can do is a two-stage build. On the first stage, build just libc++
(ninja cxx cxxabi). On the second stage, re-configure with
-DLLVM_ENABLE_LIBCXX and build the rest of the tools. We have a downstream
builder that works this way to avoid a libstdc++ defect on the host
platform. I can't remember the exact details, can dig them up if it helps.

Cheers,

/ Asiri

[1] http://libcxx.llvm.org/docs/UsingLibcxx.html

>
> Since building all of llvm required CXX and using libcxx with the same
> version as the rest of llvm makes sense, I would certainly appreciate
> an option to build the in-tree libcxx as a first step and use it in when
> building llvm, lld, lldb, clang, ...
>
> Since llvm already builds many other DSOs it needs at runtime, adding
> libcxx is reasonable. More so if we consider that not all systems package
> libcxx at the same version as clang and llvm. For instance, Arch Linux
> has libcxx 3.8.0 but llvm and clang 3.9.0.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On Tue, Dec 27, 2016 at 3:38 PM, Asiri Rathnayake
<asiri.rathnayake at gmail.com> wrote:
>
>
> On Tue, Dec 27, 2016 at 1:29 PM, Carsten Mattner via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> When I tried to build with -DLLVM_ENABLE_LIBCXX, I found out that
>> it doesn't try to use the in-tree libcxx but looks for one built
>> and installed in the system.
>
>
> IIRC, -DLLVM_ENABLE_LIBCXX reduces to passing --stdlib=libc++ (see
> [1]) to the compiler.
>
> What you can do is a two-stage build. On the first stage, build just
> libc++ (ninja cxx cxxabi). On the second stage, re-configure with
> -DLLVM_ENABLE_LIBCXX and build the rest of the tools. We have a
> downstream builder that works this way to avoid a libstdc++ defect
> on the host platform. I can't remember the exact details, can dig
> them up if it helps.
Yes please, that would be helpful as an interim workaround.