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    SubjectRe: [PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor
    On 27 February 2012 16:27, Ian Campbell <> 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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