On Wed, 1 Aug 2012, Konrad Rzeszutek Wilk wrote:

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+struct pvclock_wall_clock {
+	u32   version;
+	u32   sec;
+	u32   nsec;
+} __attribute__((__packed__));

That is weird. It is 4+4+4 = 12 bytes? Don't you want it to be 16 bytes?

I agree that 16 bytes would be a better choice, but it needs to match
the struct in Xen that is defined as follow:

    uint32_t wc_version;      /* Version counter: see vcpu_time_info_t. */
    uint32_t wc_sec;          /* Secs  00:00:00 UTC, Jan 1, 1970.  */
    uint32_t wc_nsec;         /* Nsecs 00:00:00 UTC, Jan 1, 1970.  */

Would it make sense to add some paddigin then at least? In both
cases? Or is it too late for this?

I can see why adding some padding would be useful if the structs were
not packed and we wanted to enforce 32/64 bit compatibility on x86.
However on ARM the field alignments on 32 and 64 bits are the same for
integer values so the padding wouldn't make a difference.
In any case both structs are packed, so the alignment is forced to be the
same by the compiler.