linux-kernel - Re: [PATCH v2 16/19] gendwarfksyms: Add support for reserved structure fields

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Message-ID: <CABCJKucCWfeC0yL6Q2ZcBfef0tMd9L_gmHRJt-cUYkg_4PDtnA@mail.gmail.com>
Date: Sat, 31 Aug 2024 00:05:40 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Miroslav Benes <mbenes@...e.cz>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, Petr Pavlu <petr.pavlu@...e.com>, 
	Neal Gompa <neal@...pa.dev>, Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>, 
	Asahi Linux <asahi@...ts.linux.dev>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 16/19] gendwarfksyms: Add support for reserved
 structure fields

Hi Miroslav,

On Fri, Aug 30, 2024 at 9:34 AM Miroslav Benes <mbenes@...e.cz> wrote:
>
> yes, this is one of the approaches we use in SLES. We add kabi paddings
> to some structures in advance (see [1] as a random example) and then use
> it later if needed.
>
> It is not the only approach. Much more often we do not have a padding and
> use alignment holes ([5]), addition of a new member to the end of a
> structure ([2] or [3]) and such "tricks" ([4] for a newly fully defined
> structure).

Thanks for bringing this up! Sounds like we're also going to need a
way to completely exclude specific fields from the output then. I
think we can use a similar union approach, but instead of instructing
the tool to use another type, we can just indicate that the field
should be skipped. I'll come up with a solution for v3.

Sami