[llvm-dev] Bootstrapping with in-tree libcxx

[Asiri Rathnayake via llvm-dev]

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.
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