linux-kernel - Re: [PATCH v3 1/3] gcc-plugins: Force full rebuild when plugins change

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Message-ID: <20250507-overjoyed-coucal-from-betelgeuse-4eaa7b@l-nschier-aarch64>
Date: Wed, 7 May 2025 14:10:55 +0200
From: Nicolas Schier <nicolas.schier@...ux.dev>
To: Kees Cook <kees@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	linux-hardening@...r.kernel.org, linux-kbuild@...r.kernel.org,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Justin Stitt <justinstitt@...gle.com>,
	Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>, linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com, llvm@...ts.linux.dev
Subject: Re: [PATCH v3 1/3] gcc-plugins: Force full rebuild when plugins
 change

On Wed, 07 May 2025, Nicolas Schier wrote:

> On Sat, 03 May 2025, Kees Cook wrote:
> 
> > There was no dependency between the plugins changing and the rest of the
> > kernel being built. This could cause strange behaviors as instrumentation
> > could vary between targets depending on when they were built.
> > 
> > Generate a new header file, gcc-plugins.h, any time the GCC plugins
> > change. Include the header file in compiler-version.h when its associated
> > feature name, GCC_PLUGINS, is defined. This will be picked up by fixdep
> > and force rebuilds where needed.
> > 
> > Add a generic "touch" kbuild command, which will be used again in
> > a following patch. Add a "normalize_path" string helper to make the
> > "TOUCH" output less ugly.
> > 
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Cc: Nicolas Schier <nicolas.schier@...ux.dev>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Cc: <linux-hardening@...r.kernel.org>
> > Cc: <linux-kbuild@...r.kernel.org>
> > ---
> >  include/linux/compiler-version.h |  4 ++++
> >  scripts/Makefile.gcc-plugins     |  2 +-
> >  scripts/Makefile.lib             | 18 ++++++++++++++++++
> >  scripts/gcc-plugins/Makefile     |  4 ++++
> >  4 files changed, 27 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/compiler-version.h b/include/linux/compiler-version.h
> > index 573fa85b6c0c..74ea11563ce3 100644
> > --- a/include/linux/compiler-version.h
> > +++ b/include/linux/compiler-version.h
> > @@ -12,3 +12,7 @@
> >   * and add dependency on include/config/CC_VERSION_TEXT, which is touched
> >   * by Kconfig when the version string from the compiler changes.
> >   */
> > +
> > +#ifdef GCC_PLUGINS
> 
> Out of curiousity:  Why can't we use CONFIG_GCC_PLUGINS here?

... because compiler-version.h is included before kconfig.h (which 
includes autoconf.h).  Sorry for the noise.