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

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Date:   Tue, 23 Feb 2021 12:54:10 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC_COMPLEXITY for s390

On Mon, Feb 22, 2021 at 08:03:31AM -0800, Guenter Roeck wrote:
> > Maybe, we can add something like CONFIG_SUPPRESS_NOISY_TESTS,
> > which is set to y by all{yes,mod}config.
> > 
> > This is self-documenting, so we do not need the '# too noisy' comment.
> > 
> > 
> > 
> > config SUPPRESS_NOISY_TESTS
> >        bool "suppress noisy test"
> > 
> > 
> > config GCC_PLUGIN_CYC_COMPLEXITY
> >         bool "Compute the cyclomatic complexity of a function" if EXPERT
> >         depends on !SUPPRESS_NOISY_TESTS
> > 
> 
> Good idea. Downside would be that it won't solve the real problem
> for s390 (which is lack of allmodconfig/allyesconfig compile test
> coverage because COMPILE_TEST isn't set anymore), but that is a
> different problem anyway, and my original patch doesn't solve
> that either.

I tried to explain why we don't want to set COMPILE_TEST for s390
anymore. It overrides architecture dependencies in Kconfig, and lots
of drivers do not set dependencies for HAS_IOMEM, HAS_DMA, and friends
correctly.
This generates constantly fallout which is irrelevant for s390 and
also for other architectures. It generates just work with close to
zero benefit. For drivers which matter for s390 we still see those
errors.

> On the other side, if that flag would be set explicitly by
> all{yes,mod}config, it would really beg for being misused. We
> might then as well add a new flag that is explicitly associated
> with all{yes,mod}config, but not with randconfig.

I think that makes most sense, probably also have a flag that is set
for randconfig.