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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Thu, 12 Apr 2018 00:55:05 +0900
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Subject: Re: [PATCH v2 19/21] gcc-plugins: test GCC plugin support in Kconfig
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kbuild <linux-kbuild@vger.kernel.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Luis R . Rodriguez" <mcgrof@kernel.org>,
        Nicolas Pitre <nico@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Emese Revfy <re.emese@gmail.com>
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2018-03-28 20:44 GMT+09:00 Kees Cook <keescook@chromium.org>:
> On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> Run scripts/gcc-plugin.sh from Kconfig.  Users can enable GCC_PLUGINS
>> only when it is supported.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> ---
>>
>> Changes in v2: None
>>
>>  arch/Kconfig                 |  4 +++
>>  scripts/Makefile.gcc-plugins | 82 ++++++++++++++++----------------------------
>>  scripts/gcc-plugin.sh        |  1 -
>>  3 files changed, 33 insertions(+), 54 deletions(-)
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index b42378d..88cc925 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -407,9 +407,13 @@ config HAVE_GCC_PLUGINS
>>           An arch should select this symbol if it supports building with
>>           GCC plugins.
>>
>> +config CC_HAS_GCC_PLUGINS
>> +       bool
>> +
>
> This doesn't seem used anywhere?
>
>>  menuconfig GCC_PLUGINS
>>         bool "GCC plugins"
>>         depends on HAVE_GCC_PLUGINS
>> +       depends on $(success $srctree/scripts/gcc-plugin.sh $HOSTCXX $CC)
>>         depends on !COMPILE_TEST
>>         help
>>           GCC plugins are loadable modules that provide extra features to the
>> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
>> index 25da4c0..19d0d5b 100644
>> --- a/scripts/Makefile.gcc-plugins
>> +++ b/scripts/Makefile.gcc-plugins
>> [...]
>> -# If plugins aren't supported, abort the build before hard-to-read compiler
>> -# errors start getting spewed by the main build.
>> -PHONY += gcc-plugins-check
>> -gcc-plugins-check: FORCE
>> -ifdef CONFIG_GCC_PLUGINS
>> -  ifeq ($(PLUGINCC),)
>> -    ifneq ($(GCC_PLUGINS_CFLAGS),)
>> -      $(Q)$(srctree)/scripts/gcc-plugin.sh --show-error $(HOSTCXX) $(CC) || true
>> -      @echo "Cannot use CONFIG_GCC_PLUGINS: your gcc installation does not support plugins, perhaps the necessary headers are missing?" >&2 && exit 1
>
> As mentioned in the other email, we lose the error reporting. Now the
> lack of plugins is just a silent =n in menuconfig.

This is the right thing to do.
Features unsupported by the compiler should be silently disable.


> Keeping
> --show-error in the Kconfig call and retaining stderr would be nice.

No.
There is no problem to use a compiler without plugin support.

If a user does not want to use plugin in the first place,
why does he/she need to be bothered by such information in stderr?


> I need to do some further testing with SANCOV, but otherwise this all
> looks correct, and my testing shows it behaving correctly.
>
> -Kees
>
> --
> Kees Cook
> Pixel Security
> --
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-- 
Best Regards
Masahiro Yamada