Messages in this thread | | | Date | Mon, 27 Feb 2012 21:05:08 +0000 | Subject | Re: [PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor | From | Peter Maydell <> |
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On 27 February 2012 16:27, Ian Campbell <Ian.Campbell@citrix.com> wrote: > R12 is not accessible from the 16 bit "T1" Thumb encoding of mov > immediate (which can only target r0..r7). > > Since we support only ARMv7+ there are "T2" and "T3" encodings available > which do allow direct mov of an immediate into R12, but are 32 bit Thumb > instructions. > > Should we use r7 instead to maximise instruction density for Thumb code?
r7 is (used by gcc as) the Thumb frame pointer; I don't know if this makes it worth avoiding in this context.
-- PMM
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