linux-kernel - Re: [PATCH v8 2/3] modpost: Produce extended MODVERSIONS information

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Message-ID: <CAGSQo03+1WjUVj-iQ6zdOST6z=p+=OqS2Xk_c4ZUdHOsxa7g2w@mail.gmail.com>
Date: Wed, 6 Nov 2024 14:19:38 -0800
From: Matthew Maurer <mmaurer@...gle.com>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Lucas De Marchi <lucas.demarchi@...el.com>, Lucas De Marchi <lucas.de.marchi@...il.com>, 
	Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Petr Pavlu <petr.pavlu@...e.com>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez <da.gomez@...sung.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, linuxppc-dev@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v8 2/3] modpost: Produce extended MODVERSIONS information

>
> > If booted against an old kernel, it will
> > behave as though there is no modversions information.
>
> Huh? This I don't get. If you have the new libkmod and boot
> an old kernel, that should just not break becauase well, long
> symbols were not ever supported properly anyway, so no regression.

Specifically, if you set NO_BASIC_MODVERSIONS, build a module, and
then load said module with a kernel *before* EXTENDED_MODVERSIONS
existed, it will see no modversion info on the module to check. This
will be true regardless of symbol length.

>
> I'm not quite sure I understood your last comment here though,
> can you clarify what you meant?
>
> Anyway, so now that this is all cleared up, the next question I have
> is, let's compare a NO_BASIC_MODVERSIONS world now, given that the
> userspace requirements aren't large at all, what actual benefits does
> using this new extended mod versions have? Why wouldn't a distro end
> up preferring this for say a future release for all modules?

I think a distro will end up preferring using this for all modules,
but was intending to put both in for a transitional period until the
new format was more accepted.

>
>   Luis