linux-kernel - Re: [PATCH] scripts/recordmcount.pl: Support build with -ffunction-sections.

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Date:	Tue, 30 Oct 2012 15:35:38 +0000
From:	Will Newton <will.newton@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scripts/recordmcount.pl: Support build with -ffunction-sections.

On Tue, Oct 30, 2012 at 3:05 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 2012-10-30 at 14:51 +0000, Will Newton wrote:
>> Scan any text section whose name begins with ".text." so
>> we will find all the functions in a kernel built with
>> -ffunction-sections.
>
> A couple of things.
>
> First, I'm very paranoid about a blanket "ok" on sections. We must
> guarantee that all sections that starts with ".text" never is freed. And
> if it is freed, that it must inform ftrace that it's about to free it
> before it does. If we can not guarantee this, then we can't do it.

I share that concern, however it looks like it should be safe. The two
architectures in tree that enable -ffunction-sections by default are
parisc and score and they both use a .text.* wildcard in their linker
script. If the support for building with --gc-sections is ever
completed then that would require -ffunction-sections and a similar
wildcard to be applied to section names.

> Second, most archs today do not use recordmcount.pl. They use the new
> recordmcount.c file.

Ok, thanks for letting me know. Is the plan to switch over to
recordmcount.c exclusively at some point?

The following architectures have some support in recordmcount.c but do
not enable it:

sh, powerpc, ia64

And the following have no support in recordmcount.c as yet:

blackfin, microblaze
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