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KVM: x86 emulator: Disable writeback for CMP emulation

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This stops "CMP r/m, reg" to write back the data into memory.
Pointed out by Avi.

The writeback suppression now covers CMP, CMPS, SCAS.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Takuya Yoshikawa 2011-04-13 00:24:55 +09:00 committed by Avi Kivity
parent be6d05cfdf
commit 575e7c1417
1 changed files with 1 additions and 1 deletions
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arch/x86/kvm/emulate.c
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@ -3671,6 +3671,7 @@ special_insn:
break;
case 0x38 ... 0x3d:
cmp: /* cmp */
c->dst.type = OP_NONE; /* Disable writeback. */
emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
break;
case 0x40 ... 0x47: /* inc r16/r32 */
@ -3797,7 +3798,6 @@ special_insn:
rc = emulate_popf(ctxt, ops, &c->dst.val, c->op_bytes);
break;
case 0xa6 ... 0xa7: /* cmps */
c->dst.type = OP_NONE; /* Disable writeback. */
goto cmp;
case 0xa8 ... 0xa9: /* test ax, imm */
goto test;