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Re: [Xen-devel] [PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor
- To: Dave Martin <dave.martin@xxxxxxxxxx>, Peter Maydell <peter.maydell@xxxxxxxxxx>
- From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
- Date: Wed, 29 Feb 2012 09:56:02 +0000
- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "linaro-dev@xxxxxxxxxxxxxxxx" <linaro-dev@xxxxxxxxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx" <kvm@xxxxxxxxxxxxxxx>, "arnd@xxxxxxxx" <arnd@xxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "catalin.marinas@xxxxxxx" <catalin.marinas@xxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 29 Feb 2012 09:56:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Wed, 2012-02-29 at 09:34 +0000, Dave Martin wrote:
> On Tue, Feb 28, 2012 at 12:28:29PM +0000, Stefano Stabellini wrote:
> > I don't have a very strong opinion on which register we should use, but
> > I would like to avoid r7 if it is already actively used by gcc.
>
> But there is no framepointer for Thumb-2 code (?)
Peter Maydell suggested there was:
> r7 is (used by gcc as) the Thumb frame pointer; I don't know if this
> makes it worth avoiding in this context.
Sounds like it might be a gcc-ism, possibly a non-default option?
Anyway, I think r12 will be fine for our purposes so the point is rather
moot.
Ian.
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