Re: [boost] Libc++ failures on linux

Subject: Re: [boost] Libc++ failures on linux
From: Deniz Bahadir (dbahadir_at_[hidden])
Date: 2017-03-11 00:32:20

Am 11.03.2017 um 00:22 schrieb Andrey Semashev via Boost:
> On Sat, Mar 11, 2017 at 1:33 AM, Tom Kent via Boost
> <boost_at_[hidden]> wrote:
>> So I tried to add my first linux regression runner using libc++ with clang,
>> and I'm seeing the following error saying it can't find <cstddef>:
>> http://www.boost.org/development/tests/develop/developer/output/teeks99-02-dc3-9-1z-lc-Docker-64on64-boost-bin-v2-libs-accumulators-test-count-test-clang-linux-3-9~c++1z~lc-debug-link-static.html
>
> That page currently shows a different error:
>
> /usr/include/c++/v1/string:1938:44: error: 'basic_string<_CharT,
> _Traits, _Allocator>' is missing exception specification 'noexcept'
> basic_string<_CharT, _Traits, _Allocator>::basic_string(const
> allocator_type& __a)
>                                            ^
> /usr/include/c++/v1/string:1326:40: note: previous declaration is here
>     _LIBCPP_INLINE_VISIBILITY explicit basic_string(const allocator_type& __a)
>
> This happens after boost/config.hpp is included, which means that
> cstddef is found. Indeed, cstddef is in /usr/include/c++/v1 on my
> system, so the compiler clearly looks there.
>
> The error itself looks like a bug in libc++.

This is a known error on Ubuntu/Debian:
https://bugs.launchpad.net/ubuntu/+source/libc++/+bug/1610168

And the fix is simple, presuming one can modify header-files of the 
libc++ installation:
http://stackoverflow.com/a/38385967

>
> /usr/include/c++/v1/cxxabi.h:21:10: fatal error: '__cxxabi_config.h'
> file not found
> #include <__cxxabi_config.h>
>
> This error is more interesting. I can see this #include in my local
> libc++ as well, yet I can't find this file on my system.
>

On my Ubuntu machine I was able to fix this error by adding the 
following path to the include-search-path: /usr/include/libcxxabi

If you do not have this path on your Ubuntu/Debian machine, you need to 
install libc++abi, too. (DEB-Package: libc++abi-dev)

> Both errors indicate that libc++ is broken on Ubuntu (or Linux in
> general) - either in upstream or in packaging. If that's the case, we
> can probably stop this testing effort right here and report the bugs
> to libc++ devs.

It is at least broken on Ubuntu/Debian regarding the problem with the 
string header.
Regarding the second error, I think the user is expected to have 
libc++abi installed (and possibly explicit link to it, too):
http://libcxx.llvm.org/docs/UsingLibcxx.html#using-libc-on-linux

> PS: If you're still having problems with cstddef, you can try seeing
> if the compiler looks in /usr/include/c++/v1 as described here:
>
> http://stackoverflow.com/questions/11946294/dump-include-paths-from-g
>
> If it doesn't, try adding it as an include path. Although, that path
> obviously should be used by default when libc++ is enabled.
>

Hope that helps,
Deniz