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

Catalin Marinas
2011-12-01T16:57:18Z

On Thu, Dec 01, 2011 at 04:44:40PM +0000, Arnd Bergmann wrote:
> On Thursday 01 December 2011, Catalin Marinas wrote:
> > On Thu, Dec 01, 2011 at 03:42:19PM +0000, Arnd Bergmann wrote:
> > > On Thursday 01 December 2011, Catalin Marinas wrote:
> > > 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.
> >
> > If you treat it as an "int" (32-bit) and function prototype defined
> > accordingly, then the generated code only accesses it as a W (rather
> > than X) register and the top 32-bit part is ignored (no need for
> > sign-extension). If it is defined as a "long" in the 32-bit world, then
> > it indeed needs explicit conversion given the different sizes for long
> > (for example sys_lseek, the second argument is a 'long' and we do
> > explicit sign extension in the wrapper).
...
> What about unsigned long and pointer? Can we always rely on the upper
> half of the register to be zero-filled when we get an exception from 32
> bit into 64 bit state, or do we also have to zero-extend those?

They are also fine, no need for zero-extension.

--
Catalin