Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

Jeremy Fitzhardinge
2007-03-18T15:58:23Z

Andi Kleen wrote:
>> The idea is _NOT_ that you go look for references to the paravirt_ops
>> members structure, that would be stupid and you wouldn't be able to
>> use the most efficient addressing mode on a given cpu, you'd be
>> patching up indirect calls and crap like that. Just say no...
>>
>
> That wouldn't handle inlines though. At least some of the current
> paravirtops like cli/sti are critical enough to require inlining.
>

You could special-case it in the thing handling the relocs; if you're
relocating to point to a function which you have an inline substitution,
then inline.

The bigger problem is that you don't know what registers you can
clobber. For the pv_ops in hand-written asm, that a big pain. The code
either has to assume the worst, or the "relocator" has to do something
more sophisticated (like look for push/pop pairs surrounding the call,
perhaps?).

J