[U-Boot] RFC: Aligning arch initialisation sequences

[Reinhard Meyer]

On 13.11.2010 07:31, Reinhard Meyer wrote:
> Dear Graeme Russ, Dear All,
>> On 10/11/10 10:35, Mike Frysinger wrote:
>>> On Sunday, November 07, 2010 05:06:26 Graeme Russ wrote:
>>>> Should all architectures strive to look as much like one another as
>>>> possible? Should we accept that maybe this particular issue be thrown in
>>>> the too hard basket?
>>>
>>> imo, we should strive to have these things in one common place and not just
>>> have the different files look the sam
>>
>> I was afraid someone would say that. I've been having a look and a think
>> about the situation for x86, and I cannot come up with a sane way to
>> emulate the way the global data pointer is handled by the other arches.
>>
>> I essence, the gd pointer is a unique global variable available prior to
>> relocation. On all other arches, this is achieved by using a reserved
>> register which I do not have the luxury of on x86 :(
>>
>> Unless I can resolve this, I cannot move x86 in line with the other arches
>> (i.e. init functions can only be done after relocation).
>
> <Ducks><Flame shield>
> I *personally* prefer code without tool-chain specific, out of "C"
> constructs. So I would be fine with passing gd as a parameter to all
> pre-relocation functions. The way they are called with a function array
> that would probably only marginally increase code size. And instead of
> all the funky stack calculations to get the space for gd, it could be
> achieved in a much simpler way:
>
> in asm: set stack to end (or begin) of SRAM (or whatever)
>
> in c:
> board_early_init(void)
> {
> 	gd_t	auto_gd;
> 	...
> 	call all pre-relocation functions with&auto_gd as parameter
> 	...
> 	relocate and fixup (preferably in C) - would probably
> 	have arch-specific parts in the ELF fix-up
> 	...
> 	memcpy (&static_gd,&auto_gd, sizeof auto_gd);
> 	...
> 	setup final stack and jump to relocated code...
> 	that should be a *small* assembly helper function
> }
>
> You get the idea ;)
>
> </Flame Shield></Ducks>

Ok, ok, I forgot the hitch that some functions called from
the pre-relocation functions also would need the auto_gd passed on,
*if* they need to use gd. That might become ugly, but x86 has solved
that somehow?

Best Regards,
Reinhard