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>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 22fdf0ac66151c8296fd8ef1682704733e31027b..84e536603f5ae109621c488950a87b6149a93e65 100644 (file)
--- 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;