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

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Message-ID: <hs5fxluchiconuonhziu3qh2ol5bsdxva3cuny2mit4i3equzt@ieueiius5x4w>
Date: Thu, 7 Nov 2024 00:27:07 -0600
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Matthew Maurer <mmaurer@...gle.com>
CC: Luis Chamberlain <mcgrof@...nel.org>, 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

On Wed, Nov 06, 2024 at 02:19:38PM -0800, Matthew Maurer wrote:
>>
>> > 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

how are you setting NO_BASIC_MODVERSIONS and loading it in a kernel
that still doesn't have that, i.e. before EXTENDED_MODVERSIONS?

Please Cc me on the format change and if possible submit the libkmod
support.

thanks
Lucas De Marchi

>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