Re: [Xen-devel] [Android-virt] [Embeddedxen-devel] [ANNOUNCE] Xen port to Cortex-A15 / ARMv7 with virt extensions

[Arnd Bergmann <arnd@xxxxxxxx>]

On Thursday 01 December 2011, Catalin Marinas wrote:
> Given the way register banking is done on AArch64, issuing an HVC on a
> 32-bit guest OS doesn't require translation on a 64-bit hypervisor. We
> have a similar implementation at the SVC level (for 32-bit user apps on
> a 64-bit kernel), the only modification was where a 32-bit SVC takes a
> 64-bit parameter in two separate 32-bit registers, so packing needs to
> be done in a syscall wrapper.

How do you deal with signed integer arguments passed into SVC or HVC from
a caller? If I understand the architecture correctly, the upper
halves of the argument register end up zero-padded, while the callee
expects sign-extension.

        Arnd

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