On 13/11/10 19:20, Albert ARIBAUD wrote:
Le 13/11/2010 05:16, Graeme Russ a écrit :
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 :(
Dusting off ooooold knowledge of x86 and without even a glance at x86 u-boot... Since GD is the only global used pre-reloc, can you not ensure it always ends up first in the data segment, and then manage two values for the DS segment reg, one pre-reloc where only gd can be used, and one post-reloc where gd and all the other globals can be accessed?
I had though of something similar to that by using GS (which is not generally used by u-boot) but it is very messy
All segments are currently setup to be full 4GB with the initial descriptor table hard-coded in flash and then reloaded after relocation (it needs to be reloaded so it does not get clobbered when erasing flash or relocating from RAM). I did have a dynamic GTD calculated in asm using self modifying code but changed that out to use the same 'C' methodology as Linux. I would prefer not to go back there...
So yes, it is possible, but quite frankly, I would rather leave the init functions post relocation than mess around with the GTS pre-relocation
Regards,
Graeme