| Message ID | 20180103173952.10834-1-yann.morin.1998@free.fr |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [RFC] core/infra: fix build on toolchain without C++ | expand |
Hello, On Wed, 3 Jan 2018 18:39:52 +0100, Yann E. MORIN wrote: > Autotools-based packages that do not need C++ but check for it, and use > libtool, will fail to configure on distros that lack /lib/cpp. > > This is the case for example on Arch Linux, where expat fails to build > with: > > configure: error: in `/home/dkc/src/buildroot/build/build/expat-2.2.4': > configure: error: C++ preprocessor "/lib/cpp" fails sanity check > > This is because libtool uses AC_PROC_CXXCPP, which can not be avoided, > and does require a cpp that passes some "sanity" checks (does not choke > on valid input, but does choke on invalid input). So we can use neither > /bin/false nor /bin/true... > > We instead need something that can digest some basic C++ preprocessor > input. We can't use the target preprocessor: that does not work, because > it obviously has no C++ cupport: > > arm-linux-cpp.br_real: error: conftest.cpp: C++ compiler not > installed on this system > > We can however consider that the host machine does have a C++ compiler, > so we use the host' cpp, which is gcc's compiler wrapper that ends up > calling the host's C++ preprocessor. > > That would give us a valid C++ preprocessor when we don't have one, in > fact. But autotools will then correctly fail anyway, because there is > indeed no C++ compiler at all, as we can see in this excerpt of a > configure log from expat: > > checking whether we are using the GNU C++ compiler... no > checking whether false accepts -g... no > checking dependency style of false... none > checking how to run the C++ preprocessor... cpp > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > libtool.m4: error: problem compiling CXX test program > checking for false option to produce PIC... -DPIC > checking if false PIC flag -DPIC works... no > checking if false static flag works... no > checking if false supports -c -o file.o... no > checking if false supports -c -o file.o... (cached) no > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > > So, using the host's C++ preprocessor (by way of gcc's wrapper) leads to > a working situation, where the end result is as expected. > > 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: Vivien Didelot <vivien.didelot@savoirfairelinux.com> > Cc: Peter Korsgaard <peter@korsgaard.com> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> > --- > package/Makefile.in | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Applied to master, thanks. Thomas
>>>>> "Yann" == Yann E MORIN <yann.morin.1998@free.fr> writes: > Autotools-based packages that do not need C++ but check for it, and use > libtool, will fail to configure on distros that lack /lib/cpp. > This is the case for example on Arch Linux, where expat fails to build > with: > configure: error: in `/home/dkc/src/buildroot/build/build/expat-2.2.4': > configure: error: C++ preprocessor "/lib/cpp" fails sanity check > This is because libtool uses AC_PROC_CXXCPP, which can not be avoided, > and does require a cpp that passes some "sanity" checks (does not choke > on valid input, but does choke on invalid input). So we can use neither > /bin/false nor /bin/true... > We instead need something that can digest some basic C++ preprocessor > input. We can't use the target preprocessor: that does not work, because > it obviously has no C++ cupport: > arm-linux-cpp.br_real: error: conftest.cpp: C++ compiler not > installed on this system > We can however consider that the host machine does have a C++ compiler, > so we use the host' cpp, which is gcc's compiler wrapper that ends up > calling the host's C++ preprocessor. > That would give us a valid C++ preprocessor when we don't have one, in > fact. But autotools will then correctly fail anyway, because there is > indeed no C++ compiler at all, as we can see in this excerpt of a > configure log from expat: > checking whether we are using the GNU C++ compiler... no > checking whether false accepts -g... no > checking dependency style of false... none > checking how to run the C++ preprocessor... cpp > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > libtool.m4: error: problem compiling CXX test program > checking for false option to produce PIC... -DPIC > checking if false PIC flag -DPIC works... no > checking if false static flag works... no > checking if false supports -c -o file.o... no > checking if false supports -c -o file.o... (cached) no > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > So, using the host's C++ preprocessor (by way of gcc's wrapper) leads to > a working situation, where the end result is as expected. > 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: Vivien Didelot <vivien.didelot@savoirfairelinux.com> > Cc: Peter Korsgaard <peter@korsgaard.com> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Committed to 2017.11.x, thanks.
>>>>> "Yann" == Yann E MORIN <yann.morin.1998@free.fr> writes: > Autotools-based packages that do not need C++ but check for it, and use > libtool, will fail to configure on distros that lack /lib/cpp. > This is the case for example on Arch Linux, where expat fails to build > with: > configure: error: in `/home/dkc/src/buildroot/build/build/expat-2.2.4': > configure: error: C++ preprocessor "/lib/cpp" fails sanity check > This is because libtool uses AC_PROC_CXXCPP, which can not be avoided, > and does require a cpp that passes some "sanity" checks (does not choke > on valid input, but does choke on invalid input). So we can use neither > /bin/false nor /bin/true... > We instead need something that can digest some basic C++ preprocessor > input. We can't use the target preprocessor: that does not work, because > it obviously has no C++ cupport: > arm-linux-cpp.br_real: error: conftest.cpp: C++ compiler not > installed on this system > We can however consider that the host machine does have a C++ compiler, > so we use the host' cpp, which is gcc's compiler wrapper that ends up > calling the host's C++ preprocessor. > That would give us a valid C++ preprocessor when we don't have one, in > fact. But autotools will then correctly fail anyway, because there is > indeed no C++ compiler at all, as we can see in this excerpt of a > configure log from expat: > checking whether we are using the GNU C++ compiler... no > checking whether false accepts -g... no > checking dependency style of false... none > checking how to run the C++ preprocessor... cpp > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > libtool.m4: error: problem compiling CXX test program > checking for false option to produce PIC... -DPIC > checking if false PIC flag -DPIC works... no > checking if false static flag works... no > checking if false supports -c -o file.o... no > checking if false supports -c -o file.o... (cached) no > checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes > So, using the host's C++ preprocessor (by way of gcc's wrapper) leads to > a working situation, where the end result is as expected. > 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: Vivien Didelot <vivien.didelot@savoirfairelinux.com> > Cc: Peter Korsgaard <peter@korsgaard.com> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Committed to 2017.02.x, thanks.
diff --git a/package/Makefile.in b/package/Makefile.in index a1a5316051..61f0a8f9d0 100644 --- a/package/Makefile.in +++ b/package/Makefile.in @@ -398,7 +398,7 @@ NLS_OPTS = --disable-nls endif ifneq ($(BR2_INSTALL_LIBSTDCPP),y) -TARGET_CONFIGURE_OPTS += CXX=false +TARGET_CONFIGURE_OPTS += CXX=false CXXCPP=cpp endif ifeq ($(BR2_STATIC_LIBS),y)
Autotools-based packages that do not need C++ but check for it, and use libtool, will fail to configure on distros that lack /lib/cpp. This is the case for example on Arch Linux, where expat fails to build with: configure: error: in `/home/dkc/src/buildroot/build/build/expat-2.2.4': configure: error: C++ preprocessor "/lib/cpp" fails sanity check This is because libtool uses AC_PROC_CXXCPP, which can not be avoided, and does require a cpp that passes some "sanity" checks (does not choke on valid input, but does choke on invalid input). So we can use neither /bin/false nor /bin/true... We instead need something that can digest some basic C++ preprocessor input. We can't use the target preprocessor: that does not work, because it obviously has no C++ cupport: arm-linux-cpp.br_real: error: conftest.cpp: C++ compiler not installed on this system We can however consider that the host machine does have a C++ compiler, so we use the host' cpp, which is gcc's compiler wrapper that ends up calling the host's C++ preprocessor. That would give us a valid C++ preprocessor when we don't have one, in fact. But autotools will then correctly fail anyway, because there is indeed no C++ compiler at all, as we can see in this excerpt of a configure log from expat: checking whether we are using the GNU C++ compiler... no checking whether false accepts -g... no checking dependency style of false... none checking how to run the C++ preprocessor... cpp checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes libtool.m4: error: problem compiling CXX test program checking for false option to produce PIC... -DPIC checking if false PIC flag -DPIC works... no checking if false static flag works... no checking if false supports -c -o file.o... no checking if false supports -c -o file.o... (cached) no checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes So, using the host's C++ preprocessor (by way of gcc's wrapper) leads to a working situation, where the end result is as expected. 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: Vivien Didelot <vivien.didelot@savoirfairelinux.com> Cc: Peter Korsgaard <peter@korsgaard.com> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> --- package/Makefile.in | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)