Re: [PATCH 1/6] Add infrastructure for conditional code and data sections

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

On Wed, 22 Dec 2010 10:28:41 -0800
Tony Lindgren <tony@atomide.com> wrote:

> > Nice to see that the idea is welcome. Did you had a look at the
> > implementation in patch 1/6 ?
> 
> No not yet, will take a look after we're done with this upcoming
> merge window..

Great, thanks.

> Ideally the new sections would be arch/arm generic sections and not
> omap specific. I could see ARMv6 and ARMv7 sections being one way
> to group them, but that does not help to drop omap3 specific data
> on omap4.

The mechanism is architecture independent, not OMAP-specific or even
ARM-specific (the only architecture-dependent part is the modification
of the kernel linker script, but it's trivial to adapt to other arches).
You can put as many sections as you want, you just need to declare some
macros:

#define __something_data cond_data_section(something)
#define __something_text cond_text_section(something)

and then mark whatever you want with __something_data or
__something_text. It will then be part of separate sections, that are
page-aligned so that they can independently be freed.

For the moment, the API allows to tell which sections you want to
*free*, but I think I should turn it into an API that allows to tell
which sections you want to *keep*. This way, if you have sections for
100 machines and you boot on a given machine, you only need to say "I'm
using this section". At the end of the kernel boot process, all
sections that have not been marked as useful would be removed.

Regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com