linux-kernel - Re: [PATCH v7 1/6] Shared library support

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Date:	Thu, 5 May 2016 20:40:08 +0200
From:	Emese Revfy <re.emese@...il.com>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	kernel-hardening@...ts.openwall.com,
	Michal Marek <mmarek@...e.com>,
	Kees Cook <keescook@...omium.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Brown <david.brown@...aro.org>
Subject: Re: [PATCH v7 1/6] Shared library support

On Wed, 4 May 2016 13:09:05 +0900
Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> Hi Emese,
> 
> 
> 2016-05-04 6:29 GMT+09:00 Emese Revfy <re.emese@...il.com>:
> > On Tue, 3 May 2016 11:00:56 +0900
> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
> >
> > Hi,
> >
> >> # Compile .c file, create position independent .o file
> >> # host-cxxshobjs -> .o
> >> quiet_cmd_host-cxxshobjs = HOSTCXX -fPIC $@
> >>       cmd_host-cxxshobjs = $(HOSTCXX) $(hostcxx_flags) -fPIC -c -o $@ $<
> >>                            $(host-cxxshobjs): $(obj)/%.o: $(src)/%.c FORCE
> >>                            $(call if_changed_dep,host-cxxshobjs)
> >>
> >>
> >>
> >>
> >> We generally use HOSTCC to compile *.c files,
> >> and HOSTCXX to compile *.cc files.
> >>
> >>
> >> But, here, you mention to use HOSTCXX to compile .c files
> >> such as cyc_complexity_plugin.c, sancov_plugin.c, etc.
> >>
> >> This is not straight-forward.  It is worthwhile to comment the reason.
> >
> > I wrote a comment about it here:
> > https://github.com/ephox-gcc-plugins/gcc-plugins_linux-next/commit/74f6343a7f13c071e00c417332051e25f15009ea
> >
> 
> 
> 
> +# Note that plugin capable gcc versions can be either C or C++ based
> +# therefore plugin source files have to be compilable in both C and C++ mode.
> +# This is why a C++ compiler is invoked on a .c file.
> 
> Thanks.
> 
> Please let me confirm if I understood correctly.
> 
> 
> We generally have to do something with the name-space conflict
> (with 'extern "C"') in the mixture of C/C++.
> 
> Depending on the GCC version,
> GCC-plugin-related libraries could be built for C or C++.
> 
> So, we need to check the GCC version and choose correct one
> from C or C++.

The plugin source files have to be compilable by both versions
because gcc versions 4.5 and 4.6 are compiled by a C compiler,
gcc-4.7 can be compiled by a C or a C++ compiler,
and versions 4.8+ can only be compiled by a C++ compiler.

-- 
Emese