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

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Message-ID: <b9b17126-9af5-2f73-526e-91bb9fd27f71@samsung.com>
Date:   Fri, 18 Dec 2020 08:57:56 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        linux-hardening@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

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