Date:   Fri, 18 Dec 2020 15:33:36 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Masahiro Yamada <masahiroy@...nel.org>
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>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test


On 18/12/2020 15:12, Jon Hunter wrote:
> 
> On 18/12/2020 15:09, Marek Szyprowski wrote:
>>
>> On 18.12.2020 16:03, Jon Hunter wrote:
>>> On 18/12/2020 10:05, Marek Szyprowski wrote:
>>>> On 18.12.2020 10:43, Masahiro Yamada wrote:
>>>>> On Fri, Dec 18, 2020 at 4:58 PM Marek Szyprowski
>>>>> <m.szyprowski@...sung.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@...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://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@...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
>>>> Indeed, it was missing on my setup. Sorry for the noise.
>>>
>>> So this change also breaks the build on our farm build machines and
>>> while we can request that packages are installed on these machines, it
>>> takes time. Is there anyway to avoid this?
>>
>> You can temporarily revert 1e860048c53e (this patch).
> 
> 
> Again that works locally, but these automated builders just pull the
> latest -next branch and build.


However, if you are saying that this is a problem/bug with our builders,
then of course we will have to get this fixed.

Jon

-- 
nvpublic

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