x86_emulate: fix EFLAGS setting of CMPXCHG emulation

CMPXCHG sets CF, PF, AF, SF, and OF flags according to the results of the
comparison the rAX with the operand of the instruction.
rAX must be the first argument of the comparison (a minuend), the operand
must be the second one (a subtrahend).

Due to improper order of comparison arguments, CF, PF, AF, SF and OF flags were
set incorrectly in the case of inequality. Need to swap them.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>

test_x86_emulate: extend EFLAGS check of CMPXCHG test

CMPXCHG: in the case of inequality of the rAX and the operand,
need to check CF, PF, AF, SF and OF flags as well.

This adjustment covers the fix of incorrect comparison during
CMPXCHG emulation.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>

master commit: 2232628ecb
master date: 2015-05-04 11:55:41 +0200
master commit: 20fd4b70a7
master date: 2015-05-04 12:03:19 +0200

tools/tests/x86_emulator/test_x86_emulator.c

@@ -286,7 +286,7 @@ int main(int argc, char **argv)
     rc = x86_emulate(&ctxt, &emulops);
     if ( (rc != X86EMUL_OKAY) || 
          (*res != 0x923456AA) || 
-         ((regs.eflags&0x240) != 0x200) ||
+         ((regs.eflags&0xad5) != 0xa91) ||
          (regs.eax != 0xAABBCCAA) ||
          (regs.ecx != 0xFF) ||
          (regs.eip != (unsigned long)&instr[4]) )

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -4257,7 +4257,8 @@ x86_emulate(
         /* Save real source value, then compare EAX against destination. */
         src.orig_val = src.val;
         src.val = _regs.eax;
-        emulate_2op_SrcV("cmp", src, dst, _regs.eflags);
+        /* cmp: %%eax - dst ==> dst and src swapped for macro invocation */
+        emulate_2op_SrcV("cmp", dst, src, _regs.eflags);
         if ( _regs.eflags & EFLG_ZF )
         {
             /* Success: write back to memory. */