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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>
- From: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
- Date: Fri, 9 Mar 2012 11:20:20 -0500 (EST)
- Cc: Richard Earnshaw <Richard.Earnshaw@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "linaro-dev@xxxxxxxxxxxxxxxx" <linaro-dev@xxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, "arnd@xxxxxxxx" <arnd@xxxxxxxx>, Catalin Marinas <Catalin.Marinas@xxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx" <kvm@xxxxxxxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 09 Mar 2012 16:20:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
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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