linux-kernel - Re: [PATCH 00/15] Implement MODVERSIONS for Rust

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Message-ID: <CABCJKuc5FRn2STrmg1zR_xXrvuTnFp+m6GudRN1O4bMr8YWKeQ@mail.gmail.com>
Date: Thu, 18 Jul 2024 10:04:02 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Petr Pavlu <petr.pavlu@...e.com>, Masahiro Yamada <masahiroy@...nel.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 00/15] Implement MODVERSIONS for Rust

On Tue, Jul 16, 2024 at 12:12 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> > After replacement:
> >
> >     union {
> >             u64 new_member;
> >             struct {
> >                     u8 __kabi_reserved_1[8];
> >             };
> >     }
>
> Note, such a thing would only be for the distros that want it, you can
> add support for this to the tool, but there is no need for any
> __kabi_reserved fields in mainline.

Sure. I assume modversions are primarily useful for distros, so I just
want to make sure this scheme can handle all the common issues as
well.

> > Greg, I know you've been dealing with this for a long time, any thoughts?
>
> It's a good start, yes.  Also watch out for when structures go from
> "anonymous" to "fully described" when new #include lines get added to
> files.  The current tooling has issues with that, so we need to use
> __GENKSYMS__ #ifdef lines in some places to keep crc generation stable.
> Don't know if dwarf output would be susceptible to the same issues with
> that or not, but you should check.

That's a great point. DWARF output has the exact same problem if a
structure declaration later becomes a definition, but I think we can
come up with a solution for this issue too in v2.

Sami