linux-kernel - Re: [PATCH 00/14] scripts/sorttable: ftrace: Remove place holders for weak functions in available_filter

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Message-ID: <20250102164454.2ffa33b1@gandalf.local.home>
Date: Thu, 2 Jan 2025 16:44:54 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.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>, Peter Zijlstra <peterz@...radead.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 00/14] scripts/sorttable: ftrace: Remove place holders
 for weak functions in available_filter_functions

On Thu, 2 Jan 2025 11:30:12 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Please just do this by sorting non-existent functions at the end,
> instead of just zeroing them out.
> 
> That makes the mcount_loc table dense in valid entries. We could then
> just rewrite the size of the table (or just add a variable containing
> the size, if you don't want to change ELF metadata - but you're
> already sorting the table, so why not?)

Well, I tried to move the __start_mcount_loc, but it appears that changing
the symbol value *after* the linking phase does nothing :-p  The references
to it have already been resolved. The Elf_Rel* will do the updates from
then on, and to read those, becomes architecture dependent.

I guess the next thing I could do is to create a "skip" variable that can
be modified, and we can skip X entries in the start_mcount_loc. As the
start_mcount_loc and stop_mcount_loc (which determines the size of the
table) cannot be modified in an architecture independent way.

-- Steve