linux-kernel - Re: [PATCH] kallsyms, livepatch: Fix livepatch with CONFIG_LTO

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Message-ID: <ZoZlGnVDzVONxUDs@pathway.suse.cz>
Date: Thu, 4 Jul 2024 11:02:18 +0200
From: Petr Mladek <pmladek@...e.com>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
	Sami Tolvanen <samitolvanen@...gle.com>, Song Liu <song@...nel.org>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	jikos@...nel.org, joe.lawrence@...hat.com, nathan@...nel.org,
	morbo@...gle.com, justinstitt@...gle.com,
	thunder.leizhen@...wei.com, kees@...nel.org, kernel-team@...a.com
Subject: Re: [PATCH] kallsyms, livepatch: Fix livepatch with CONFIG_LTO_CLANG

On Wed 2024-07-03 08:30:33, Luis Chamberlain wrote:
> On Tue, Jul 02, 2024 at 10:56:41PM -0700, Josh Poimboeuf wrote:
> > On Mon, Jul 01, 2024 at 03:13:23PM +0200, Petr Mladek wrote:
> > > So, you suggest to search the symbols by a hash. Do I get it correctly?
> 
> I meant, that in the Rust world the symbols go over the allowed limit,
> and so an alternative for them is to just use a hash. What I'm
> suggesting is for a new kconfig option where that world is the
> new one, so that they have to also do the proper userspace tooling
> for it. Without that, I don't see it as properly tested or scalable.
> And if we're gonna have that option for Rust for modules, then it begs
> the question if this can be used by other users.

I am still not sure at which level the symbol names would get hashed ;-)

The symbols names are used in many situations, e.g. backtraces,
crashdump, objdump, nm, gdb, tracing, livepatching, kprobes, ...

Would kallsyms provide some translation table between the usual
"long" symbol name and a hash?

Would it allows to search the symbols both ways?


I am a bit scared because using hashed symbol names in backtraces, gdb,
... would be a nightmare. Hashes are not human readable and
they would complicate the life a lot. And using different names
in different interfaces would complicate the life either.

Best Regards,
Petr