linux-kernel - Re: [PATCH] gcc-plugins: make it possible to disable CONFIG_GCC

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Message-ID: <CAKv+Gu8yaz8uekq3taUaxWOs95yVB_tRaoKM0N2EBKSzWOhExw@mail.gmail.com>
Date:   Wed, 11 Dec 2019 14:59:23 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Emese Revfy <re.emese@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] gcc-plugins: make it possible to disable
 CONFIG_GCC_PLUGINS again

On Wed, 11 Dec 2019 at 14:40, Arnd Bergmann <arnd@...db.de> wrote:
>
> I noticed that randconfig builds with gcc no longer produce a lot of
> ccache hits, unlike with clang, and traced this back to plugins
> now being enabled unconditionally if they are supported.
>
> I am now working around this by adding
>
>    export CCACHE_COMPILERCHECK=/usr/bin/size -A %compiler%
>
> to my top-level Makefile. This changes the heuristic that ccache uses
> to determine whether the plugins are the same after a 'make clean'.
>
> However, it also seems that being able to just turn off the plugins is
> generally useful, at least for build testing it adds noticeable overhead
> but does not find a lot of bugs additional bugs, and may be easier for
> ccache users than my workaround.
>
> Fixes: 9f671e58159a ("security: Create "kernel hardening" config area")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Ard Biesheuvel <ardb@...nel.org>

> ---
>  scripts/gcc-plugins/Kconfig | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
> index d33de0b9f4f5..e3569543bdac 100644
> --- a/scripts/gcc-plugins/Kconfig
> +++ b/scripts/gcc-plugins/Kconfig
> @@ -14,8 +14,8 @@ config HAVE_GCC_PLUGINS
>           An arch should select this symbol if it supports building with
>           GCC plugins.
>
> -config GCC_PLUGINS
> -       bool
> +menuconfig GCC_PLUGINS
> +       bool "GCC plugins"
>         depends on HAVE_GCC_PLUGINS
>         depends on PLUGIN_HOSTCC != ""
>         default y
> @@ -25,8 +25,7 @@ config GCC_PLUGINS
>
>           See Documentation/core-api/gcc-plugins.rst for details.
>
> -menu "GCC plugins"
> -       depends on GCC_PLUGINS
> +if GCC_PLUGINS
>
>  config GCC_PLUGIN_CYC_COMPLEXITY
>         bool "Compute the cyclomatic complexity of a function" if EXPERT
> @@ -113,4 +112,4 @@ config GCC_PLUGIN_ARM_SSP_PER_TASK
>         bool
>         depends on GCC_PLUGINS && ARM
>
> -endmenu
> +endif
> --
> 2.20.0
>