Re: [Xen-devel] [PATCH 5/5] xen: Add V4V implementation - padding question

[Tim Deegan <tim@xxxxxxx>]

At 13:10 -0400 on 11 Jun (1370956242), Ross Philipson wrote:
> >
> >>>...
> >>>+struct v4v_info
> >>>+{
> >>>+    uint64_t ring_magic;
> >>>+    uint64_t data_magic;
> >>>+    evtchn_port_t evtchn;
> >>
> >>Missing padding at the end?
> >>
> >
> >ack.
> >
> 
> At one point during the review of an earlier version of the V4V patch 
> set, Jan requested that this pad be added to the v4v_info struct. I 
> understand the padding in all the other structs but I don't understand 
> this one. This struct is not included in any other structs and is not 
> followed by any data.

64-bit Xen would see this as a 24-byte struct, even without explicit
padding.  That would surprise a 32-bit guest that allocated what it saw
as a 20-byte struct for Xen to copy into.

Tim.

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