linux-kernel - Re: [RFC] [PATCH] x86: Use ELF section to list CPU vendor specific code (Linux Tiny)

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Message-ID: <20080225185358.19fff688@crazy>
Date:	Mon, 25 Feb 2008 18:53:58 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Linux-tiny@...enic.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	michael@...e-electrons.com
Subject: Re: [RFC] [PATCH] x86: Use ELF section to list CPU vendor specific
 code (Linux Tiny)

Le Mon, 25 Feb 2008 09:03:12 -0800,
Matt Mackall <mpm@...enic.com> a écrit :

> > > This is not quite what Peter and I were thinking of, I think.
> > > It's not at all generic. How about a section that simply contains
> > > a set of function pointers, a macro to add things to that
> > > section, and a function that calls all the pointers in that
> > > section. Eg:
> > > 
> > > CALLBACK_SECTION(init_cpu_amd, "cpuvendor.init");
> > > invoke_callback_section("cpuvendor.init");
> > > 
> > > ..which would give us a generic facility we could use in various
> > > places.
> > 
> > I see. Probably doable. How would it work in the LD script file ?
> > Your mechanism allows to specify any section name, but AFAIK, the
> > sections must be explicitly listed in the kernel LD script in order
> > to be included in the final kernel image. Am I missing something ?
> 
> I can't see any way to avoid it, but we can leave it to future
> generations to come up with something more clever.

After a quick look at the LD documentation, it seems that wildcards are
supported in the input section names of the linker script. So that the
CALLBACK_SECTION() macro could add the function pointer to a section
named:

   gcm. ## name

(gcm standing for "generic callback mechanism") and then, in the linker
script, do:

   *(gcm.*)

I'm going to try that.

Sincerly,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Free Embedded Linux Training Materials
on http://free-electrons.com/training
(More than 1500 pages!)

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