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

[Marek Szyprowski]

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@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx>
>>>>> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
>>>> 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.
>
> 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).

Best regards

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