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Subject: Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Emese Revfy <re.emese@gmail.com>,
        linux-hardening@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <9f959875-1a30-b1a1-b626-3805e24a6df3@samsung.com>
Date:   Fri, 18 Dec 2020 11:05:21 +0100
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On 18.12.2020 10:43, Masahiro Yamada wrote:
> On Fri, Dec 18, 2020 at 4:58 PM Marek Szyprowski
> <m.szyprowski@samsung.com> wrote:
>> 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://protect2.fireeye.com/v1/url?k=03db90e1-5c40a828-03da1bae-0cc47a336fae-4cc36f5830aeb78d&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Flore.kernel.org%2Flkml%2FCAHk-%3DwjU4DCuwQ4pXshRbwDCUQB31ScaeuDo1tjoZ0_PjhLHzQ%40mail.gmail.com%2F
>>> [2] https://protect2.fireeye.com/v1/url?k=965b670a-c9c05fc3-965aec45-0cc47a336fae-e34339513ff747c0&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Flore.kernel.org%2Flkml%2FCAHk-%3DwhK0aQxs6Q5ijJmYF1n2ch8cVFSUzU5yUM_HOjig%3D%2Bvnw%40mail.gmail.com%2F
>>>
>>> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
>>> Signed-off-by: Masahiro Yamada <masahiroy@kernel.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://protect2.fireeye.com/v1/url?k=053727b6-5aac1f7f-0536acf9-0cc47a336fae-5bd799e7ce6b1b9b&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Freleases.linaro.org%2Fcomponents%2Ftoolchain%2Fbinaries%2F 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
>>
>
> I can compile gcc-plugins with Linaro toolchians.
>
> The version of mine is this:
>
> masahiro@oscar:~/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

Indeed, it was missing on my setup. Sorry for the noise.

Best regards

-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland