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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 06/08/12 15:44, 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.

A comment next to the #define of the two macros?

>> 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.

Ignore this.  Dunno what I was thinking.

David

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