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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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.

> How does this check work (without g++) on a non-clang build?

It works because on a non-clang Alpine build g++ wasn't installed, so
the check wasd just skipped. The headers++.chk target in
xen/include/Makefile has a explicit check for a functional CXX.

I do think this is some kind of error in the Alpine clang package, as
I assume installing clang++ without the standard c++ headers is an
error. Regardless of that, I also think installing g++ on the Alpine
container is fine, as we would then also perform the C++ header checks
with g++ on the normal build.

Thanks, Roger.