[Buildroot] [PATCHv2] core: alternate solution to disable C++

Peter Seiderer ps.report at gmx.net
Thu Mar 29 16:25:17 UTC 2018


On Thu, 29 Mar 2018 00:08:08 +0200, Arnout Vandecappelle <arnout at mind.be> wrote:

> On 27-03-18 21:40, Peter Seiderer wrote:
> > Hello Yann,
> > 
> > On Tue, 27 Mar 2018 13:00:22 +0200, "Yann E. MORIN" <yann.morin.1998 at free.fr> wrote:
> >   
> >> Some packages that use libtool really need some love to be able to
> >> disable C++ support.
> >>
> >> This is because libtool will want to call AC_PROG_CXXCPP as soon as CXX
> >> is set non-empty to something different from 'no'. Then, AC_PROG_CXXCPP
> >> will want a C++ preprocessor that works on valid input *and* fail on
> >> invalid input.
> >>
> >> So, providing 'false' as the C++ compiler will then require that we do
> >> have a working C++ preprocessor. Which is totally counter-productive
> >> since we do not have a C++ compiler to start with...
> >>
> >> bd39d11d2e (core/infra: fix build on toolchain without C++) was a
> >> previous attempt at fixing this, by using the host's C++ preprocessor.
> >>
> >> However, that is very incorrect (that's my code, I can say so!) because
> >> the set of defines will most probably be different for the host and the
> >> target, thus causign all sorts of trouble. For example, on ARM we'd have
> >> to include different headers for soft-float vs hard-float, which is
> >> decided based on a macro, which is not defined for x86, and thus may
> >> redirect to the wrong (and missing) header.
> >>
> >> Instead, we notice that libtool uses the magic value 'no' to decide that
> >> a C++ compiler is not available, in which case it skeips the call to
> >> AC_PROG_CXXCPP.
> >>
> >> Given that 'no' is not provided by any package in Debian and
> >> derivatives, as well as in Fedora, we can assume that no system will
> >> have an executable called 'no'. Hence, we use that as a magic value to
> >> disable C++ detection altogether.
> >>
> >> Fixes: #10846 (again)  
> > 
> > Fixes the gnutls configure failure described in Bug-10846...
> > 
> > Tested-by: Peter Seiderer <ps.report at gmx.net>  
> 
>  Does that also imply that your earlier patch [1] can be marked as Superseded?

Yes...

Regards,
Peter

> 
>  Regards,
>  Arnout
> 
> [1] http://patchwork.ozlabs.org/patch/889057/
> 
> > 
> > Regards,
> > Peter  
> [snip]
> 




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