Re: [PATCH for-4.15] automation/alpine: add g++ to the list of build depends

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: <xen-devel@lists.xenproject.org>,
	Doug Goldstein <cardoe@cardoe.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Ian Jackson <iwj@xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH for-4.15] automation/alpine: add g++ to the list of build depends
Date: Tue, 2 Mar 2021 10:36:51 +0100	[thread overview]
Message-ID: <YD4HM9+IEZKIq/SQ@Air-de-Roger> (raw)
In-Reply-To: <b3912fde-165c-b404-bf1c-46189d0ce766@suse.com>

On Tue, Mar 02, 2021 at 09:53:41AM +0100, Jan Beulich wrote:
> On 02.03.2021 09:14, Roger Pau Monné wrote:
> > On Mon, Mar 01, 2021 at 06:01:36PM +0000, Andrew Cooper wrote:
> >> On 01/03/2021 17:59, Andrew Cooper wrote:
> >>> On 01/03/2021 09:58, Roger Pau Monne wrote:
> >>>> clang++ relies on the C++ headers installed by g++, or else a clang
> >>>> build will hit the following error:
> >>>>
> >>>> <built-in>:3:10: fatal error: 'cstring' file not found
> >>>> #include "cstring"
> >>>>          ^~~~~~~~~
> >>>> 1 error generated.
> >>>> make[10]: *** [Makefile:120: headers++.chk] Error 1
> >>>>
> >>>> Reported-by: Stefano Stabellini <sstabellini@kernel.org>
> >>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> >>>> ---
> >>>> Cc: Ian Jackson <iwj@xenproject.org>
> >>>> No real risk here from a release PoV, it's just pulling a package
> >>>> required for the Alpine clang build. Worse that cold happen is that
> >>>> the Alpine clang build broke, but it's already broken.
> >>> Shouldn't this be fixed upstream in Alpine?  Its clearly a packaging bug.
> >>
> >> Or (thinking about it), we've got a build system bug using g++ when it
> >> should be using clang++.
> > 
> > No, the check is using clang++, the issue is that clang++ doesn't
> > install the standard c++ headers, and thus trying to use them (cstring
> > in this case) fails. Installing the g++ package solves the issue
> > because it installs the headers.
> 
> I have to admit that I consider this odd. The g++ package should
> neither provide nor depend on the headers. It may recommend their
> installation. On my distro (SLES) the headers come from the
> libstdc++-devel package, as I would have expected. There
> additionally is a dependency of libclang5 (no -devel suffix!) on
> libstdc++-devel (I suppose this is an indication that things
> aren't quite right here either; I haven't checked an up-to-date
> version of the distro yet, though).

Yes, that was indeed my first attempt as I've tried to install
libstdc++, but there's no -devel counterpart for the package, and it
only installs the libraries but not the headers.

Then if I list the contents of the g++ package, I do see:

...
usr/include/c++/10.2.1/cstring
...

And clang++'s include path is:

#include <...> search starts here:
 /usr/bin/../lib/gcc/x86_64-alpine-linux-musl/10.2.1/../../../../include/c++/10.2.1
 /usr/bin/../lib/gcc/x86_64-alpine-linux-musl/10.2.1/../../../../include/c++/10.2.1/x86_64-alpine-linux-musl
 /usr/bin/../lib/gcc/x86_64-alpine-linux-musl/10.2.1/../../../../include/c++/10.2.1/backward
 /usr/include
 /usr/lib/clang/10.0.1/include

So it does seem clang depends on the gcc c++ headers, I assume this is
done in order to avoid having a duplicate set of c++ headers for clang
and gcc? I really have no idea, but I do think clang package should
depend on g++.

Thanks, Roger.