linux-kernel - Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

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Date:   Fri, 18 Dec 2020 18:43:12 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        linux-hardening@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

On Fri, Dec 18, 2020 at 4:58 PM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> Hi,
>
> On 03.12.2020 13:57, Masahiro Yamada wrote:
> > Linus pointed out a third of the time in the Kconfig parse stage comes
> > from the single invocation of cc1plus in scripts/gcc-plugin.sh [1],
> > and directly testing plugin-version.h for existence cuts down the
> > overhead a lot. [2]
> >
> > This commit takes one step further to kill the build test entirely.
> >
> > The small piece of code was probably intended to test the C++ designated
> > initializer, which was not supported until C++20.
> >
> > In fact, with -pedantic option given, both GCC and Clang emit a warning.
> >
> > $ echo 'class test { public: int test; } test = { .test = 1 };' | g++ -x c++ -pedantic - -fsyntax-only
> > <stdin>:1:43: warning: C++ designated initializers only available with '-std=c++2a' or '-std=gnu++2a' [-Wpedantic]
> > $ echo 'class test { public: int test; } test = { .test = 1 };' | clang++ -x c++ -pedantic - -fsyntax-only
> > <stdin>:1:43: warning: designated initializers are a C++20 extension [-Wc++20-designator]
> > class test { public: int test; } test = { .test = 1 };
> >                                            ^
> > 1 warning generated.
> >
> > Otherwise, modern C++ compilers should be able to build the code, and
> > hopefully skipping this test should not make any practical problem.
> >
> > Checking the existence of plugin-version.h is still needed to ensure
> > the plugin-dev package is installed. The test code is now small enough
> > to be embedded in scripts/gcc-plugins/Kconfig.
> >
> > [1] https://lore.kernel.org/lkml/CAHk-=wjU4DCuwQ4pXshRbwDCUQB31ScaeuDo1tjoZ0_PjhLHzQ@mail.gmail.com/
> > [2] https://lore.kernel.org/lkml/CAHk-=whK0aQxs6Q5ijJmYF1n2ch8cVFSUzU5yUM_HOjig=+vnw@mail.gmail.com/
> >
> > Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>
> This patch landed in linux next-20201217 as commit 1e860048c53e
> ("gcc-plugins: simplify GCC plugin-dev capability test").
>
> It causes a build break with my tests setup, but I'm not sure weather it
> is really an issue of this commit or a toolchain I use. However I've
> checked various versions of the gcc cross-compilers released by Linaro
> at https://releases.linaro.org/components/toolchain/binaries/ and all
> fails with the same error:
>
> $ make ARCH=arm
> CROSS_COMPILE=../../cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/arm-none-eabi-
> zImage
>    HOSTCXX scripts/gcc-plugins/arm_ssp_per_task_plugin.so
> In file included from
> /home/mszyprow/dev/cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.2.1/plugin/include/gcc-plugin.h:28:0,
>                   from scripts/gcc-plugins/gcc-common.h:7,
>                   from scripts/gcc-plugins/arm_ssp_per_task_plugin.c:3:
> /home/mszyprow/dev/cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.2.1/plugin/include/system.h:687:10:
> fatal error: gmp.h: No such file or directory
>   #include <gmp.h>
>            ^~~~~~~
> compilation terminated.
> scripts/gcc-plugins/Makefile:47: recipe for target
> 'scripts/gcc-plugins/arm_ssp_per_task_plugin.so' failed
> make[2]: *** [scripts/gcc-plugins/arm_ssp_per_task_plugin.so] Error 1
> scripts/Makefile.build:496: recipe for target 'scripts/gcc-plugins' failed
> make[1]: *** [scripts/gcc-plugins] Error 2
> Makefile:1190: recipe for target 'scripts' failed
> make: *** [scripts] Error 2
>
> Compilation works if I use the cross-gcc provided by
> gcc-7-arm-linux-gnueabi/gcc-arm-linux-gnueabi Ubuntu packages, which is:
>
> $ arm-linux-gnueabi-gcc --version
> arm-linux-gnueabi-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0
>
> Best regards
>
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>


I can compile gcc-plugins with Linaro toolchians.

The version of mine is this:

masahiro@...ar:~/ref/linux-next$
~/tools/arm-linaro-7.5/bin/arm-linux-gnueabihf-gcc --version
arm-linux-gnueabihf-gcc (Linaro GCC 7.5-2019.12) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.




Maybe, it depends on the host environment?


Please try this:

$ sudo apt install libgmp-dev



-- 
Best Regards
Masahiro Yamada