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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 02.03.2021 10:36, Roger Pau Monné wrote:
> 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@xxxxxxxxxx>
>>>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>>>> ---
>>>>>> Cc: Ian Jackson <iwj@xxxxxxxxxxxxxx>
>>>>>> 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++.

As long as the g++ package is what provides the headers (i.e. if that's
their concept), I agree.

Jan