[cfe-dev] about the "Attempt to fix stdint/cstdint modules try 2" commit

[Eric Fiselier via cfe-dev]

On Thu, May 25, 2017 at 1:41 AM, René J.V. Bertin <rjvbertin at gmail.com>
wrote:

> Eric Fiselier wrote on 20170524::21:58:56 re: "Re: [cfe-dev] about the
> "Attempt to fix stdint/cstdint modules try 2" commit"
>
> >Just to be clear, You're attempting to build GCC 6.3 using Clang, and
> >you've hacked up the GCC build so that it always uses libc++ instead of
> >libstdc++?
>
> - I use clang for the initial bootstrap build (which is perfectly possible
> and nothing new), afterwards GCC builds itself. Multiple times.
> - yes, I have a hack that causes the resulting compiler to use the c++
> headers from clang, and libc++
> - the hack is supposed to evolve into support for a `-stdlib` feature like
> clang has
>
> >Why are you forcing GCC to build against libc++ in the first place? What's
> >the benefit? Doesn't the build default to bootstrapping and using a
> >bootstrapped libstdc++?
>
> GCC itself is built against its usual static copy of libstdc++ and family
> (in the end that works out more reliably).
> The benefit of my approach is simple and sufficiently obvious that the GCC
> team will consider the change once implemented properly. It's the only way
> G++ can be used on systems that use libc++ as the system C++ runtime
> without taking extreme precautions. It's not impossible to run binaries
> that use the libstdc++ runtime on Mac, but in practice they should not use
> any system SDKs that are written in C++, to avoid passing objects between
> libc++ and libstdc++.
>
> >AFAIK the GCC build doesn't use Boost, so IDK how Boost is getting into
> the
> >mix.
>
> No, it doesn't. I ran into an issue building software using boost, and
> boost itself, when using the "libc++ enabled g++".
>

Are you sure you were using g++ and not clang++ (via c++ or some other
weird symlink)?
GCC doesn't support Clang Modules (e.g. module maps), so you can't have
been running into a modules if you were using GCC 6.3.

/Eric



> I've had the time to look into this further since asking here, and
> discovered that Boost has a number of places where it assumes that libc++
> is used only together with clang. When I patched those the issues went
> away, at least on OS X 10.9 .
>
> >I would assume the issue *would* be present in the OS X's system libc++
> >installation, (assuming the system installation hasn't been updated to
> >include the fix, which it likely hasn't)
>
> No, I haven't updated the system libc++. I have a more recent libc++
> installed to the side (from the MacPorts package) which I insert into
> applications I run from a shell, but that doesn't help with anything that
> sneaks in at link time (or is run via the Finder).
>
> But if I understand correctly the issue is relatively recent, and should
> thus not yet be present in installations that are now several years old,
> correct?
>
> R.
>
>
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