Date: Mon, 25 Feb 2008 18:53:58 +0100
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
To: Matt Mackall <mpm@selenic.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Linux-tiny@selenic.com,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       michael@free-electrons.com
Subject: Re: [RFC] [PATCH] x86: Use ELF section to list CPU vendor specific
 code (Linux Tiny)
Message-ID: <20080225185358.19fff688@crazy>
In-Reply-To: <1203958992.7461.46.camel@cinder.waste.org>
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Le Mon, 25 Feb 2008 09:03:12 -0800,
Matt Mackall <mpm@selenic.com> a =C3=A9crit :

> > > 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:
> > >=20
> > > CALLBACK_SECTION(init_cpu_amd, "cpuvendor.init");
> > > invoke_callback_section("cpuvendor.init");
> > >=20
> > > ..which would give us a generic facility we could use in various
> > > places.
> >=20
> > 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 ?
>=20
> 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
--=20
Thomas Petazzoni, Free Electrons
Free Embedded Linux Training Materials
on http://free-electrons.com/training
(More than 1500 pages!)

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