linux-kernel - Re: [PATCH v2 1/3] gcc-plugins: Force full rebuild when plugins change

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Message-ID: <202505031023.BC44DC842@keescook>
Date: Sat, 3 May 2025 10:25:57 -0700
From: Kees Cook <kees@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	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>,
	Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
	linux-um@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] gcc-plugins: Force full rebuild when plugins
 change

On Sat, May 03, 2025 at 03:12:23PM +0900, Masahiro Yamada wrote:
> On Sat, May 3, 2025 at 7:54 AM Kees Cook <kees@...nel.org> wrote:
> > +quiet_cmd_gcc_plugins_updated = UPDATE  $@
> > +      cmd_gcc_plugins_updated = echo '/* $^ */' > $(obj)/gcc-plugins-deps.h
> 
> I think 'touch' should be enough.
> 
> If some plugins are disabled, it is detected by the normal if_changed rule.

I kind of likely having the active plugins show up in there, but yes,
"touch" is enough (it's what I started with originally).

> > +$(obj)/gcc-plugins-deps.h: $(plugin-single) $(plugin-multi) FORCE
> > +       $(call if_changed,gcc_plugins_updated)
> > +
> > +always-y += gcc-plugins-deps.h
> > --
> > 2.34.1
> >
> 
> 
> I think it is simpler to place the header
> in include/generated/.

I couldn't figure out how to do this, but thankfully you did! :)

> I attached my suggestion below:
> [...]
> -quiet_cmd_gcc_plugins_updated = UPDATE  $@
> -      cmd_gcc_plugins_updated = echo '/* $^ */' > $(obj)/gcc-plugins-deps.h
> +quiet_cmd_gcc_plugins_updated = TOUCH   $@
> +      cmd_gcc_plugins_updated = touch $@
> 
> -$(obj)/gcc-plugins-deps.h: $(plugin-single) $(plugin-multi) FORCE
> +$(obj)/../../include/generated/gcc-plugins-deps.h: $(plugin-single)
> $(plugin-multi) FORCE
>         $(call if_changed,gcc_plugins_updated)
> 
> -always-y += gcc-plugins-deps.h
> +always-y += ../../include/generated/gcc-plugins-deps.h

Aaagh, thank you! I didn't even consider trying ".." for targets!

Yes, this is SO much better! I will read your other replies and work on
v3...

-- 
Kees Cook