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

On 06/11/2013 01:25 PM, Tim Deegan wrote:
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?


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.

Ah yes, of course. Thanks for the quick response.



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