KVM: x86 emulator: cmps instruction

Add emulation for the cmps instruction.  This lets OpenBSD boot on kvm.

Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@ext.bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 56 insertions, 2 deletions

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 22fdf0ac6615..84e536603f5a 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1535,10 +1535,31 @@ special_insn:
                 break;
         }
         if (c->rep_prefix) {
+                /* All REP prefixes have the same first termination condition */
                 if (c->regs[VCPU_REGS_RCX] == 0) {
                         ctxt->vcpu->rip = c->eip;
                         goto done;
                 }
+                /* The second termination condition only applies for REPE
+                 * and REPNE. Test if the repeat string operation prefix is
+                 * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
+                 * corresponding termination condition according to:
+                 *      - if REPE/REPZ and ZF = 0 then done
+                 *      - if REPNE/REPNZ and ZF = 1 then done
+                 */
+                if ((c->b == 0xa6) || (c->b == 0xa7) ||
+                                (c->b == 0xae) || (c->b == 0xaf)) {
+                        if ((c->rep_prefix == REPE_PREFIX) &&
+                                ((ctxt->eflags & EFLG_ZF) == 0)) {
+                                        ctxt->vcpu->rip = c->eip;
+                                        goto done;
+                        }
+                        if ((c->rep_prefix == REPNE_PREFIX) &&
+                                ((ctxt->eflags & EFLG_ZF) == EFLG_ZF)) {
+                                ctxt->vcpu->rip = c->eip;
+                                goto done;
+                        }
+                }
                 c->regs[VCPU_REGS_RCX]--;
                 c->eip = ctxt->vcpu->rip;
         }
@@ -1564,8 +1585,41 @@ special_insn:
                                                            : c->dst.bytes);
                 break;
         case 0xa6 ... 0xa7:     /* cmps */
-                DPRINTF("Urk! I don't handle CMPS.\n");
-                goto cannot_emulate;
+                c->src.type = OP_NONE; /* Disable writeback. */
+                c->src.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
+                c->src.ptr = (unsigned long *)register_address(
+                                c->override_base ? *c->override_base :
+                                                   ctxt->ds_base,
+                                                   c->regs[VCPU_REGS_RSI]);
+                if ((rc = ops->read_emulated((unsigned long)c->src.ptr,
+                                                &c->src.val,
+                                                c->src.bytes,
+                                                ctxt->vcpu)) != 0)
+                        goto done;
+
+                c->dst.type = OP_NONE; /* Disable writeback. */
+                c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
+                c->dst.ptr = (unsigned long *)register_address(
+                                                   ctxt->es_base,
+                                                   c->regs[VCPU_REGS_RDI]);
+                if ((rc = ops->read_emulated((unsigned long)c->dst.ptr,
+                                                &c->dst.val,
+                                                c->dst.bytes,
+                                                ctxt->vcpu)) != 0)
+                        goto done;
+
+                DPRINTF("cmps: mem1=0x%p mem2=0x%p\n", c->src.ptr, c->dst.ptr);
+
+                emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
+
+                register_address_increment(c->regs[VCPU_REGS_RSI],
+                                       (ctxt->eflags & EFLG_DF) ? -c->src.bytes
+                                                                  : c->src.bytes);
+                register_address_increment(c->regs[VCPU_REGS_RDI],
+                                       (ctxt->eflags & EFLG_DF) ? -c->dst.bytes
+                                                                  : c->dst.bytes);
+
+                break;
         case 0xaa ... 0xab:     /* stos */
                 c->dst.type = OP_MEM;
                 c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;