linux-kernel - RE: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules

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Date:   Mon, 8 Mar 2021 09:39:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Josh Poimboeuf' <jpoimboe@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        "Linux Kbuild mailing list" <linux-kbuild@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Justin Forbes <jforbes@...hat.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Frank Eigler <fche@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT
 modules

> - "External modules must be built with the same GCC version"
> 
>   As has been stated repeatedly, by Linus and others, there's no
>   technical reason behind this claim.  It ignores the realities of how
>   distros release the kernel and compiler independently, with separate
>   cadences.  Minor variances in compiler version are ABI compatible.

Aren't major versions ABI compatible?
Otherwise it is a different architecture.

>   Also, for features which are dependent on compiler version, many of
>   those are now enabled by kbuild.  As I suggested to you previously,
>   kbuild should warn when such features get disabled (which can happen
>   due to a compiler/toolchain change or due to a .config copied from
>   another system).

Anything that is just an optimisation (or pessimisation) really
doesn't matter.
AFAICT most of these options are in the latter category.

One think people might do is download a kernel from kernel.org
and then build an extra module for it.
The compiler they have will be completely different.

	David

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