linux-hardening - Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC

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Message-ID: <YDOeI5+1H3T1ocmQ@osiris>
Date:   Mon, 22 Feb 2021 13:05:55 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC_COMPLEXITY for s390

On Sun, Feb 21, 2021 at 02:56:50PM -0800, Guenter Roeck wrote:
> Commit 334ef6ed06fa ("init/Kconfig: make COMPILE_TEST depend on !S390") disabled
> COMPILE_TEST for s390. At the same time, "make allmodconfig/allyesconfig" for
> s390 is still supported. However, it generates thousands of compiler
> messages such as the following, making it highly impractical to run.
> 
> Cyclomatic Complexity 1 scripts/mod/devicetable-offsets.c:main
> Cyclomatic Complexity 1 scripts/mod/devicetable-offsets.c:_GLOBAL__sub_I_00100_0_main
> 
> Since GCC_PLUGIN_CYC_COMPLEXITY is primarily used for testing, disable it
> when building s390 images.
> 
> Cc: Arnd Bergmann <arnd@...nel.org>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Fixes: 334ef6ed06fa ("init/Kconfig: make COMPILE_TEST depend on !S390")
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>  scripts/gcc-plugins/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
> index ab9eb4cbe33a..5e9bb500f443 100644
> --- a/scripts/gcc-plugins/Kconfig
> +++ b/scripts/gcc-plugins/Kconfig
> @@ -21,7 +21,7 @@ if GCC_PLUGINS
>  
>  config GCC_PLUGIN_CYC_COMPLEXITY
>  	bool "Compute the cyclomatic complexity of a function" if EXPERT
> -	depends on !COMPILE_TEST	# too noisy
> +	depends on !COMPILE_TEST && !S390	# too noisy

I don't see a reason to disable this in general for s390. COMPILE_TEST
was only disabled for s390 because a lot of irrelevant configs didn't
compile and it would cause a lot of unnecessary work to fix that.

However the !COMPILE_TEST dependency here looks more like it was
misused in lack of a possibility to detect if the config was generated
with allyesconfig/allmodconfig. Maybe that could be added somehow to
Kconfig?