[PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor
Richard.Earnshaw at arm.com
Fri Mar 9 17:38:38 UTC 2012
On 09/03/12 16:20, Nicolas Pitre wrote:
> On Fri, 9 Mar 2012, Dave Martin wrote:
>> Register variables feel like a red herring though. We're only using
>> those because we can't do the needful thing and actually desscribe
>> these constraints in the asm constraints (which would seem to be the
>> right place). We specifically don't care where those values are
>> except at the boundaries of the asm block itself.
>> Is there a reason why ARM gcc doesn't provide the ability to specify
>> such exact-register constraints, or is this more for historical
>> reasons? It is possible?
> I don't know how much things have changed since I last looked at the gcc
> code, but implementing this seemed to be pretty trivial at the time.
> The problem would be to determine a good letter scheme to map to actual
While it is technically possible, it is likely to end up hurting overall
compiler performance as we'll then have to define the machine as having
small register classes.
Richard Earnshaw Email: Richard.Earnshaw at arm.com
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