On 13/11/10 17:38, Reinhard Meyer wrote:
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?
Yes, by declaring gd as a global (static) variable and only referencing it after relocation (well actually, it is passed as a parameter to board_init_f (in lieu of boot_params) where the relocation is performed
Regards,
Graeme