linux-kernel - Re: [PATCH v3 0/3] Detect changed compiler dependencies for full rebuild

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Message-ID: <202505080855.DF4FB68A@keescook>
Date: Thu, 8 May 2025 08:56:07 -0700
From: Kees Cook <kees@...nel.org>
To: Nicolas Schier <nicolas.schier@...ux.dev>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.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,
	linux-hardening@...r.kernel.org, linux-kbuild@...r.kernel.org,
	kasan-dev@...glegroups.com, llvm@...ts.linux.dev
Subject: Re: [PATCH v3 0/3] Detect changed compiler dependencies for full
 rebuild

On Wed, May 07, 2025 at 02:02:42PM +0200, Nicolas Schier wrote:
> On Sat, 03 May 2025, Kees Cook wrote:
> 
> >  v3: move to include/generated, add touch helper
> >  v2: https://lore.kernel.org/lkml/20250502224512.it.706-kees@kernel.org/
> >  v1: https://lore.kernel.org/lkml/20250501193839.work.525-kees@kernel.org/
> > 
> > Hi,
> > 
> > This is my attempt to introduce dependencies that track the various
> > compiler behaviors that may globally change the build that aren't
> > represented by either compiler flags nor the compiler version
> > (CC_VERSION_TEXT). Namely, this is to detect when the contents of a
> > file the compiler uses changes. We have 3 such situations currently in
> > the tree:
> > 
> > - If any of the GCC plugins change, we need to rebuild everything that
> >   was built with them, as they may have changed their behavior and those
> >   behaviors may need to be synchronized across all translation units.
> >   (The most obvious of these is the randstruct GCC plugin, but is true
> >   for most of them.)
> > 
> > - If the randstruct seed itself changes (whether for GCC plugins or
> >   Clang), the entire tree needs to be rebuilt since the randomization of
> >   structures may change between compilation units if not.
> > 
> > - If the integer-wrap-ignore.scl file for Clang's integer wrapping
> >   sanitizer changes, a full rebuild is needed as the coverage for wrapping
> >   types may have changed, once again cause behavior differences between
> >   compilation units.
> 
> I am unsure if it is too much detail, but I'd like to see some of these 
> infos in include/linux/compiler-version.h, too.

Yeah, that's a good idea. No reason to make people dig for the commit
logs, etc -- it should be immediately discoverable. I've updated the
patches to include the (slight rephrased) text above.

Thanks!

-- 
Kees Cook