Re: [Xen-devel] [PATCH 0/5] ARM hypercall ABI: 64 bit ready

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 6 Aug 2012, Stefano Stabellini wrote:
> On Mon, 6 Aug 2012, David Vrabel wrote:
> > On 06/08/12 15:11, Stefano Stabellini wrote:
> > > Hi all,
> > > this patch series makes the necessary changes to make sure that the
> > > current ARM hypercall ABI can be used as-is on 64 bit ARM platforms:
> > > 
> > > - it defines xen_ulong_t as uint64_t on ARM;
> > > - it introduces a new macro to handle guest pointers, called
> > > XEN_GUEST_HANDLE_PARAM (that has size 4 bytes on aarch and is going to
> > > have size 8 bytes on aarch64);
> > > - it replaces all the occurrences of XEN_GUEST_HANDLE in hypercall
> > > parameters with XEN_GUEST_HANDLE_PARAM.
> > 
> > This is a subtle (and undocumented!) distinction. I can see people
> > adding/modifying hypercall etc. getting this wrong and no one noticing
> > for a while (since it doesn't affect x86).
> 
> Where should I document this? I wrote it into the commit message but
> maybe a doc under docs is better.
> 
> 
> > The xen_ulong_t parameters (when used for pointers) from an aarch guest
> > point of view are a uint32_t guest pointer and uint32_t of padding.  So
> > the guest handles will be the same size in hypercall parameters and
> > structure members.
> 
> I changed xen_ulong_t to be 64 bit on ARM
> 

Sorry, pressed "send" too soon.

I don't think there are any xen_ulong_t used for pointers in hypercall
parameters, at least there are none in the hypercalls we are using so
far.

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