[PATCH 05/10] KVM: emulate: share common register decoding code

Paolo Bonzini
2025-11-14T00:36:43Z

Remove all duplicate handling of register operands, including picking
the right register class and fetching it, by extracting a new function
that can be used for both REG and MODRM operands.

Centralize setting op->orig_val = op->val in fetch_register_operand()
as well.

No functional change intended.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/emulate.c | 49 +++++++++++++++---------------------------
1 file changed, 17 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 7ef791407dbc..6c8d3f786e74 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1026,6 +1026,7 @@ static void fetch_register_operand(struct operand *op)
op->val = *(u64 *)op->addr.reg;
break;
}
+ op->orig_val = op->val;
}

static int em_fninit(struct x86_emulate_ctxt *ctxt)
@@ -1071,16 +1072,9 @@ static int em_fnstsw(struct x86_emulate_ctxt *ctxt)
return X86EMUL_CONTINUE;
}

-static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
- struct operand *op)
+static void __decode_register_operand(struct x86_emulate_ctxt *ctxt,
+ struct operand *op, int reg)
{
- unsigned int reg;
-
- if (ctxt->d & ModRM)
- reg = ctxt->modrm_reg;
- else
- reg = (ctxt->b & 7) | ((ctxt->rex_prefix & 1) << 3);
-
if (ctxt->d & Sse) {
op->type = OP_XMM;
op->bytes = 16;
@@ -1099,9 +1093,20 @@ static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
op->type = OP_REG;
op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
op->addr.reg = decode_register(ctxt, reg, ctxt->d & ByteOp);
-
fetch_register_operand(op);
- op->orig_val = op->val;
+}
+
+static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
+ struct operand *op)
+{
+ unsigned int reg;
+
+ if (ctxt->d & ModRM)
+ reg = ctxt->modrm_reg;
+ else
+ reg = (ctxt->b & 7) | ((ctxt->rex_prefix & 1) << 3);
+
+ __decode_register_operand(ctxt, op, reg);
}

static void adjust_modrm_seg(struct x86_emulate_ctxt *ctxt, int base_reg)
@@ -1128,24 +1133,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
ctxt->modrm_seg = VCPU_SREG_DS;

if (ctxt->modrm_mod == 3 || (ctxt->d & NoMod)) {
- op->type = OP_REG;
- op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
- op->addr.reg = decode_register(ctxt, ctxt->modrm_rm,
- ctxt->d & ByteOp);
- if (ctxt->d & Sse) {
- op->type = OP_XMM;
- op->bytes = 16;
- op->addr.xmm = ctxt->modrm_rm;
- kvm_read_sse_reg(ctxt->modrm_rm, &op->vec_val);
- return rc;
- }
- if (ctxt->d & Mmx) {
- op->type = OP_MM;
- op->bytes = 8;
- op->addr.mm = ctxt->modrm_rm & 7;
- return rc;
- }
- fetch_register_operand(op);
+ __decode_register_operand(ctxt, op, ctxt->modrm_rm);
return rc;
}

@@ -4619,14 +4607,12 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
op->addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX);
fetch_register_operand(op);
- op->orig_val = op->val;
break;
case OpAccLo:
op->type = OP_REG;
op->bytes = (ctxt->d & ByteOp) ? 2 : ctxt->op_bytes;
op->addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX);
fetch_register_operand(op);
- op->orig_val = op->val;
break;
case OpAccHi:
if (ctxt->d & ByteOp) {
@@ -4637,7 +4623,6 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
op->bytes = ctxt->op_bytes;
op->addr.reg = reg_rmw(ctxt, VCPU_REGS_RDX);
fetch_register_operand(op);
- op->orig_val = op->val;
break;
case OpDI:
op->type = OP_MEM;
--
2.43.5