Messages in this thread | | | Date | Fri, 9 Mar 2012 11:20:20 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor |
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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.
Absolutely.
> 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 registers.
Nicolas
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