From: Luis Chamberlain <mcgrof@kernel.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Nick Alcock <nick.alcock@oracle.com>,
masahiroy@kernel.org, linux-modules@vger.kernel.org,
linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org,
arnd@arndb.de, akpm@linux-foundation.org, eugene.loh@oracle.com,
kris.van.hees@oracle.com, live-patching@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH modules-next v10 00/13] kallsyms: reliable symbol->address lookup with /proc/kallmodsyms
Date: Mon, 24 Apr 2023 12:47:39 -0700 [thread overview]
Message-ID: <ZEbc20oRFR0f8Qj6@bombadil.infradead.org> (raw)
In-Reply-To: <20230407232118.o2x5lakfgyzy56gz@treble>
On Fri, Apr 07, 2023 at 04:21:18PM -0700, Josh Poimboeuf wrote:
> Anyway, I was nodding along with the above cover letter until I got to
> the third paragraph.
>
> A "built-in kernel module" is not actually a module, as it's built in to
> vmlinux. I suspect the point is that if you rebuild with a different
> config, it might become a module. But many other changes could also
> occur with a changed config, including changed inlining decisions and
> GCC IPA optimization function renaming, in which case the symbol might
> no longer exist with the new config.
Yes it does not matter, for his tooling effort it was just to be able
to map a possible module to a symbol so tooling can display this to
disambiguate.
> Also I'm confused what it means for a symbol to be "used by multiple
> modules". If the same TU or inline symbol is linked into two modules,
> it will be loaded twice at two different addresses, and the
> implementations could even differ.
He just wants to be able to map if a symbol with the same name but
different addresses is due to a built-in or a module declaration of
the same symbol so it can use it.
> It sounds like there are two problems being conflated:
>
> 1) how to uniquely identify symbols in the current kernel
>
> For this, all we really need is file+sym.
>
> Or, enable -zunique-symbols in the linker.
>
> 2) how to uniquely identify symbols across multiple kernels/configs
>
> This seems much trickier, as much can change across kernels and
> configs, including compiler inlining and naming decisions, not to
> mention actual code changes.
>
> The problems are related, but distinct.
>
> #2 seems significantly harder to implement properly.
>
> Would solving #1 give you most of what you need?
I'm not nick but my reading of his goals is that if you peg a
"possible_module" prefix or postfix or whatever, then yes.
For 2) I think it would be good to see if one could just force Kconfig
tristate to add -DPOSSIBLE_MODULE, that would be an easier approach
than the possible-obj-m thing [0] I had suggested last
[0] https://lore.kernel.org/all/Y/kXDqW+7d71C4wz@bombadil.infradead.org/
Luis
next prev parent reply other threads:[~2023-04-24 19:47 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-05 16:31 [PATCH modules-next v10 00/13] kallsyms: reliable symbol->address lookup with /proc/kallmodsyms Nick Alcock
2022-12-05 16:31 ` [PATCH v10 01/13] kbuild: add modules.builtin.objs Nick Alcock
2022-12-05 16:31 ` [PATCH v10 02/13] kbuild: bring back tristate.conf Nick Alcock
2023-03-05 8:10 ` Masahiro Yamada
2022-12-05 16:31 ` [PATCH v10 03/13] kbuild: add tristate checker Nick Alcock
2023-03-05 15:10 ` Masahiro Yamada
2022-12-05 16:31 ` [PATCH v10 04/13] kbuild: fix up substitutions in makefiles to allow for " Nick Alcock
2023-03-05 15:11 ` Masahiro Yamada
2022-12-05 16:31 ` [PATCH v10 05/13] kbuild: remove MODULE_LICENSE/AUTHOR/DESCRIPTION in non-modules Nick Alcock
2022-12-06 9:11 ` Geert Uytterhoeven
2022-12-06 20:03 ` Nick Alcock
2022-12-06 21:02 ` Arnd Bergmann
2022-12-07 5:03 ` Luis Chamberlain
2022-12-07 5:10 ` Luis Chamberlain
2022-12-07 8:21 ` Christoph Hellwig
2023-03-05 8:09 ` Masahiro Yamada
2022-12-05 16:31 ` [PATCH v10 06/13] build: add a simple iterator over modules.builtin.objs Nick Alcock
2022-12-05 16:31 ` [PATCH v10 07/13] kbuild: generate an address ranges map at vmlinux link time Nick Alcock
2022-12-05 16:31 ` [PATCH v10 08/13] kbuild: make address ranges map work with IBT Nick Alcock
2022-12-05 16:31 ` [PATCH v10 09/13] kallsyms: introduce sections needed to map symbols to built-in modules Nick Alcock
2022-12-05 16:31 ` [PATCH v10 10/13] kallsyms: optimize .kallsyms_modules* Nick Alcock
2022-12-05 16:31 ` [PATCH v10 11/13] kallsyms: distinguish text symbols fully using object file names Nick Alcock
2022-12-05 16:31 ` [PATCH v10 12/13] kallsyms: add /proc/kallmodsyms for text symbol disambiguation Nick Alcock
2022-12-05 16:31 ` [PATCH v10 13/13] perf: proof-of-concept kallmodsyms support Nick Alcock
2022-12-16 15:21 ` [PING] [PATCH modules-next v10 00/13] kallsyms: reliable symbol->address lookup with /proc/kallmodsyms Nick Alcock
2023-01-17 19:51 ` Luis Chamberlain
2023-02-09 16:54 ` Nick Alcock
2023-02-09 23:53 ` Nick Alcock
2023-02-21 21:48 ` Luis Chamberlain
2023-02-22 12:08 ` Nick Alcock
2023-02-22 22:25 ` Luis Chamberlain
2023-04-07 23:21 ` Josh Poimboeuf
2023-04-10 13:08 ` Joe Lawrence
2023-04-24 19:47 ` Luis Chamberlain [this message]
2023-04-25 8:27 ` Petr Mladek
2023-05-08 22:06 ` Steven Rostedt
2023-05-19 15:50 ` Alexander Lobakin
2023-05-22 23:21 ` Luis Chamberlain
2023-05-24 15:02 ` Nick Alcock
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