From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Korsgaard Date: Fri, 30 Mar 2018 14:25:04 +0200 Subject: [Buildroot] [PATCHv2] core: alternate solution to disable C++ In-Reply-To: <20180327110022.19980-1-yann.morin.1998@free.fr> (Yann E. MORIN's message of "Tue, 27 Mar 2018 13:00:22 +0200") References: <20180327110022.19980-1-yann.morin.1998@free.fr> Message-ID: <87tvsx699b.fsf@dell.be.48ers.dk> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net >>>>> "Yann" == Yann E MORIN writes: > 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) > Reported-by: Damien Riegel > Signed-off-by: "Yann E. MORIN" > Cc: Damien Riegel > Cc: Peter Seiderer > Cc: Vivien Didelot > Cc: Peter Korsgaard > Cc: Thomas Petazzoni > --- > Changes v1 -> v2: > - add big fat comment... Committed, thanks. -- Bye, Peter Korsgaard