tree 693f75789abbef0339db3cf7a114b963cadae5a0
parent 7dec5603b6b8dc4c3e1c65d318bd2a5a8c62a424
author Nadav Amit <namit@cs.technion.ac.il> 1402837978 +0300
committer Paolo Bonzini <pbonzini@redhat.com> 1403175129 +0200

KVM: x86: Wrong emulation on 'xadd X, X'

The emulator does not emulate the xadd instruction correctly if the two
operands are the same.  In this (unlikely) situation the result should be the
sum of X and X (2X) when it is currently X.  The solution is to first perform
writeback to the source, before writing to the destination.  The only
instruction which should be affected is xadd, as the other instructions that
perform writeback to the source use the extended accumlator (e.g., RAX:RDX).

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>