KVM: emulator: check rex prefix inside decode_register()

All decode_register() callers check if instruction has rex prefix
to properly decode one byte operand. It make sense to move the check
inside.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 282d28c..0bd372f 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -785,9 +785,10 @@ static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
  * @highbyte_regs specifies whether to decode AH,CH,DH,BH.
  */
 static void *decode_register(struct x86_emulate_ctxt *ctxt, u8 modrm_reg,
-                            int highbyte_regs)
+                            int byteop)
 {
        void *p;
+       int highbyte_regs = (ctxt->rex_prefix == 0) && byteop;
 
        if (highbyte_regs && modrm_reg >= 4 && modrm_reg < 8)
                p = (unsigned char *)reg_rmw(ctxt, modrm_reg & 3) + 1;
@@ -1024,7 +1025,6 @@ static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
                                    struct operand *op)
 {
        unsigned reg = ctxt->modrm_reg;
-       int highbyte_regs = ctxt->rex_prefix == 0;
 
        if (!(ctxt->d & ModRM))
                reg = (ctxt->b & 7) | ((ctxt->rex_prefix & 1) << 3);
@@ -1046,10 +1046,10 @@ static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
 
        op->type = OP_REG;
        if (ctxt->d & ByteOp) {
-               op->addr.reg = decode_register(ctxt, reg, highbyte_regs);
+               op->addr.reg = decode_register(ctxt, reg, true);
                op->bytes = 1;
        } else {
-               op->addr.reg = decode_register(ctxt, reg, 0);
+               op->addr.reg = decode_register(ctxt, reg, false);
                op->bytes = ctxt->op_bytes;
        }
        fetch_register_operand(op);
@@ -1082,12 +1082,10 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
        ctxt->modrm_seg = VCPU_SREG_DS;
 
        if (ctxt->modrm_mod == 3) {
-               int highbyte_regs = ctxt->rex_prefix == 0;
-
                op->type = OP_REG;
                op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
                op->addr.reg = decode_register(ctxt, ctxt->modrm_rm,
-                                              highbyte_regs && (ctxt->d & ByteOp));
+                               ctxt->d & ByteOp);
                if (ctxt->d & Sse) {
                        op->type = OP_XMM;
                        op->bytes = 16;
@@ -4117,10 +4115,8 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
        case OpMem8:
                ctxt->memop.bytes = 1;
                if (ctxt->memop.type == OP_REG) {
-                       int highbyte_regs = ctxt->rex_prefix == 0;
-
-                       ctxt->memop.addr.reg = decode_register(ctxt, ctxt->modrm_rm,
-                                              highbyte_regs);
+                       ctxt->memop.addr.reg = decode_register(ctxt,
+                                       ctxt->modrm_rm, true);
                        fetch_register_operand(&ctxt->memop);
                }
                goto mem_common;