linux-kernel - Re: [PATCH 14/14] scripts/sorttable: ftrace: Do not add weak functions to available_filter

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Message-ID: <20250102202404.GD7274@noisy.programming.kicks-ass.net>
Date: Thu, 2 Jan 2025 21:24:04 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, bpf <bpf@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Zheng Yejian <zhengyejian1@...wei.com>,
	Martin Kelly <martin.kelly@...wdstrike.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 14/14] scripts/sorttable: ftrace: Do not add weak
 functions to available_filter_functions

On Thu, Jan 02, 2025 at 02:55:01PM -0500, Steven Rostedt wrote:
> On Thu, 2 Jan 2025 20:48:14 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > *sigh*.. can we please just either add the 'hole' symbols in symtab, or
> > fix symtab to have entry size?
> > 
> > You're just fixing your one problem and leaving everybody else that has
> > extra data inside the dead weak things up a creek :/
> > 
> > Eg. if might make sense to also ignore alternative / static_branch /
> > static_call patching for such 'dead' code. Yes, that's not an immediate
> > problem atm, but just fixing __mcount_loc seems very short sighted.
> 
> Read my reply to the email that I forgot to add to the cover letter (but
> mention in the last patch). Fixing kallsyms does not remove the place
> holders in the available_filter_functions. This has nothing to do with
> kallsyms. I need to remove the fentry/mcount references in the mcount_loc
> section.
> 
> The kallsyms is a completely different issue.

It is not. If kallsyms is fixed, you can use that to tell which
fentry/mcount sites are 'invalid'.

Better yet, other people can then also tell if their things are inside
dead weak code or not.