linux-kernel - Re: [PATCH v2 00/19] Implement DWARF modversions

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Message-ID: <CABCJKud=YO=fxF_tmX1N2ec66Rzqh8RsaQu0qrbC5WB529wgWg@mail.gmail.com>
Date: Thu, 22 Aug 2024 10:57:21 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Jonathan Corbet <corbet@....net>
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 00/19] Implement DWARF modversions

Hi Jon,

On Thu, Aug 22, 2024 at 9:43 AM Jonathan Corbet <corbet@....net> wrote:
>
> Sami Tolvanen <samitolvanen@...gle.com> writes:
>
> > The first 16 patches of this series add a small tool for computing
> > symbol versions from DWARF, called gendwarfksyms. When passed a
> > list of exported symbols and an object file, the tool generates
> > an expanded type string for each symbol, and computes symbol CRCs
> > similarly to genksyms.
>
> Potentially silly question but: how similarly?  Specifically, do the two
> tools generate the same CRCs for the same symbols?  It seems that might
> be important for users transitioning to the new DWARF world order.

Reconstructing the source-based type strings genksyms uses from DWARF
wouldn't really be feasible, so the CRCs will be different. The
similar part is just that we build a human-readable string from the
debugging information and compute a CRC from it. If anyone is
interested in switching to gendwarfksyms, they'll have to rebuild all
their modules too.

Sami