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authorGravatar Yann E. MORIN <yann.morin.1998@free.fr>2018-03-27 13:00:22 +0200
committerGravatar Peter Korsgaard <peter@korsgaard.com>2018-04-06 20:06:02 +0200
commitae854d015e4005592c9de05182285a2847d8b546 (patch)
parent48d789970e20bd16583d4f455d0efd4b60ad31d8 (diff)
core: alternate solution to disable C++
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 causing 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 skips 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 <damien.riegel@savoirfairelinux.com> Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Cc: Damien Riegel <damien.riegel@savoirfairelinux.com> Cc: Peter Seiderer <ps.report@gmx.net> Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com> Cc: Peter Korsgaard <peter@korsgaard.com> Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com> Tested-by: Peter Seiderer <ps.report@gmx.net> Signed-off-by: Peter Korsgaard <peter@korsgaard.com> (cherry picked from commit 4cd1ab15886a408b897104709ff87f15cc88ba16) Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
1 files changed, 9 insertions, 1 deletions
diff --git a/package/Makefile.in b/package/Makefile.in
index e387ce67fe..57fb47ea2e 100644
--- a/package/Makefile.in
+++ b/package/Makefile.in
@@ -409,8 +409,16 @@ else
NLS_OPTS = --disable-nls
+# We need anything that is invalid. Traditionally, we'd have used 'false' (and
+# we did so in the past). However, that breaks libtool for packages that have
+# optional C++ support (e.g. gnutls), because libtool will *require* a *valid*
+# C++ preprocessor as long as CXX is not 'no'.
+# Now, whether we use 'no' or 'false' for CXX as the same side effect: it is an
+# invalid C++ compiler, and thus will cause detection of C++ to fail (which is
+# expected and what we want), while at the same time taming libtool into
+# silence.
ifeq ($(BR2_STATIC_LIBS),y)