[coreboot-gerrit] Change in coreboot[master]: [WIP] arch/x86: Refactor CAR_GLOBAL quirk for FSP1.0

[Kyösti Mälkki (Code Review)]

Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/35140 )

Change subject: [WIP] arch/x86: Refactor CAR_GLOBAL quirk for FSP1.0
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Patch Set 2:

(1 comment)

https://review.coreboot.org/c/coreboot/+/35140/2/src/cpu/x86/car.c 
File src/cpu/x86/car.c:

https://review.coreboot.org/c/coreboot/+/35140/2/src/cpu/x86/car.c@97 
PS2, Line 97: 	uintptr_t *mig_var = car_get_var_ptr(var);
> Could you add some comments here?

Yes, if patchset #2 actually works with FSP1.0...
> We're getting the migrated pointer and subtracting the value at this new slot?

My logic here is that since FSP1.0 migrates the entire _car_region (implicitly), absolute pointers to CAR region become stale, but pointers to CAR that are relative to a CAR_GLOBAL remain valid.
> So this code:
> mig_var = car_get_var_ptr(&bar.baz) /* A' */
> if (*mig_var) /* *mig_var = B */ 
>   return A' - B;

But value in *mig_var = (A - B) == -sizeof(struct foo).