[U-Boot] [U-Boot, v2] env: don't generate callback list entries for SPL

[Albert ARIBAUD]

Hi Scott,

On Tue, 12 Mar 2013 12:06:53 -0500, Scott Wood
<scottwood at freescale.com> wrote:

> On 03/12/2013 12:02:56 PM, Tom Rini wrote:
> > On Tue, Mar 12, 2013 at 11:55:22AM -0500, Scott Wood wrote:
> > > On 03/12/2013 10:30:40 AM, Tom Rini wrote:
> > > >On Fri, Mar 08, 2013 at 06:35:04PM -0600, Scott Wood wrote:
> > > >> Why would eliminating all individual callbacks cause start/end  
> > to go
> > > >> away?  If that's the way the list mechanism works, the mechanism
> > > >> needs fixing.
> > > >
> > > >Yes, that's how the mechanism works.  Rather than having to
> > > >declare that
> > > >you expect to have a linker list of name $foo, we dynamically
> > > >determine
> > > >what linker lists we have and setup the linker section entry.
> > >
> > > So it would break just as hard if we happened to turn off all of the
> > > things that register callbacks.
> > >
> > > >I'm not sure it's broken exactly, I think maybe we just need to
> > > >say no env
> > > >callback support in SPL since it's not really user editable.
> > >
> > > That's fine, but it's still a bad mechanism.
> > 
> > Yes, the mechanism has a breaking condition on trying to reference an
> > empty list (which is what SPL ends up with, in this case).  Poking
> > Albert and Marek in case they have any ideas, but this seems like a
> > feature not a bug.
> 
> How is it a feature?  One of the main benefit of linker lists is for  
> things to just work when things are configured in/out without needing  
> ifdefs and such.  Why should "everything configured out" be a special  
> case requiring an ifdef?
> 
> If we want to save some code by ifdeffing the listwalking code for SPL,  
> that's a separate matter.

Normally my reworked linker_list code should work fine with some code
going through an empty list, precisely because list start and end
symbols, like list entries, are generated by the compiler irrespective
of one another and then whatever was generated is sorted by the linker.
So an empty list ends up as two symbols at the same address (and
indeed, env callbacks, in many boards, showed this pattern in the map
file).

> -Scott

Amicalement,
-- 
Albert.