[PATCH 3/5] extract prefix decoding part from x86_emulate_memop() to x86_decode_prefix()

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

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Extract prefix decoding part from x86_emulate_memop() to x86_decode_prefix().

Signed-off-by: Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>
-- 
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  --------------
          "Software is hard" - Donald Knuth

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Index: kvm/drivers/kvm/x86_emulate.c
===================================================================
--- kvm.orig/drivers/kvm/x86_emulate.c	2007-07-31 17:44:35.000000000 +0200
+++ kvm/drivers/kvm/x86_emulate.c	2007-07-31 18:23:39.000000000 +0200
@@ -480,43 +480,24 @@
 }
 
 int
-x86_emulate_memop(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
+x86_decode_prefix(int mode, u8 *inst, struct x86_prefix *prefix)
 {
-	unsigned d;
-	u8 b, sib, twobyte = 0;
-	u8 modrm, modrm_mod = 0;
-	unsigned int i;
-	int rc = 0;
-	struct operand src, dst;
-	unsigned long cr2 = ctxt->cr2;
-	int mode = ctxt->mode;
-	unsigned long modrm_ea;
-	int use_modrm_ea, scale, rip_relative = 0;
-	int no_wb = 0;
-	u64 msr_data;
-	struct x86_prefix prefix;
-
-	/* Shadow copy of register state. Committed on successful emulation. */
-	unsigned long _regs[NR_VCPU_REGS];
-	unsigned long _eip = ctxt->vcpu->rip, _eflags = ctxt->eflags;
-	unsigned long modrm_val = 0;
-
-	memcpy(_regs, ctxt->vcpu->regs, sizeof _regs);
-	memset(&prefix, 0, sizeof(prefix));
-	prefix.override_base = -1;
+	unsigned int op_bytes, ad_bytes;
+	int i;
+	u8 b;
 
 	switch (mode) {
 	case X86EMUL_MODE_REAL:
 	case X86EMUL_MODE_PROT16:
-		prefix.op_bytes = prefix.ad_bytes = 2;
+		op_bytes = ad_bytes = 2;
 		break;
 	case X86EMUL_MODE_PROT32:
-		prefix.op_bytes = prefix.ad_bytes = 4;
+		op_bytes = ad_bytes = 4;
 		break;
 #ifdef CONFIG_X86_64
 	case X86EMUL_MODE_PROT64:
-		prefix.op_bytes = 4;
-		prefix.ad_bytes = 8;
+		op_bytes = 4;
+		ad_bytes = 8;
 		break;
 #endif
 	default:
@@ -525,39 +506,39 @@
 
 	/* Legacy prefixes. */
 	for (i = 0; i < 8; i++) {
-		switch (b = insn_fetch(u8, 1, _eip)) {
+		switch (b = inst[i]) {
 		case 0x66:	/* operand-size override */
-			prefix.op_bytes ^= 6;	/* switch between 2/4 bytes */
+			op_bytes ^= 6;	/* switch between 2/4 bytes */
 			break;
 		case 0x67:	/* address-size override */
 			if (mode == X86EMUL_MODE_PROT64)
-				prefix.ad_bytes ^= 12;	/* switch between 4/8 bytes */
+				ad_bytes ^= 12;	/* switch between 4/8 bytes */
 			else
-				prefix.ad_bytes ^= 6;	/* switch between 2/4 bytes */
+				ad_bytes ^= 6;	/* switch between 2/4 bytes */
 			break;
 		case 0x2e:	/* CS override */
-			prefix.override_base = X86EMUL_BASE_CS;
+			prefix->override_base = X86EMUL_BASE_CS;
 			break;
 		case 0x3e:	/* DS override */
-			prefix.override_base = X86EMUL_BASE_DS;
+			prefix->override_base = X86EMUL_BASE_DS;
 			break;
 		case 0x26:	/* ES override */
-			prefix.override_base = X86EMUL_BASE_ES;
+			prefix->override_base = X86EMUL_BASE_ES;
 			break;
 		case 0x64:	/* FS override */
-			prefix.override_base = X86EMUL_BASE_FS;
+			prefix->override_base = X86EMUL_BASE_FS;
 			break;
 		case 0x65:	/* GS override */
-			prefix.override_base = X86EMUL_BASE_GS;
+			prefix->override_base = X86EMUL_BASE_GS;
 			break;
 		case 0x36:	/* SS override */
-			prefix.override_base = X86EMUL_BASE_SS;
+			prefix->override_base = X86EMUL_BASE_SS;
 			break;
 		case 0xf0:	/* LOCK */
-			prefix.lock = 1;
+			prefix->lock = 1;
 			break;
 		case 0xf3:	/* REP/REPE/REPZ */
-			prefix.rep = 1;
+			prefix->rep = 1;
 			break;
 		case 0xf2:	/* REPNE/REPNZ */
 			break;
@@ -570,15 +551,62 @@
 
 	/* REX prefix. */
 	if ((mode == X86EMUL_MODE_PROT64) && ((b & 0xf0) == 0x40)) {
-		prefix.rex = b;
+		prefix->rex = b;
 		if (b & 8)
-			prefix.op_bytes = 8;	/* REX.W */
-		prefix.modrm_reg = (b & 4) << 1;	/* REX.R */
-		prefix.index_reg = (b & 2) << 2; /* REX.X */
-		prefix.modrm_rm = prefix.base_reg = (b & 1) << 3; /* REG.B */
-		b = insn_fetch(u8, 1, _eip);
+			op_bytes = 8;	/* REX.W */
+		prefix->modrm_reg = (b & 4) << 1;	/* REX.R */
+		prefix->index_reg = (b & 2) << 2; /* REX.X */
+		prefix->modrm_rm = prefix->base_reg = (b & 1) << 3; /* REG.B */
+		i++;
 	}
 
+	prefix->op_bytes = op_bytes;
+	prefix->ad_bytes = ad_bytes;
+
+	return i;
+}
+EXPORT_SYMBOL_GPL(x86_decode_prefix);
+
+int
+x86_emulate_memop(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
+{
+	unsigned d;
+	u8 b, sib, twobyte = 0;
+	u8 modrm, modrm_mod = 0;
+	int rc = 0;
+	struct operand src, dst;
+	unsigned long cr2 = ctxt->cr2;
+	int mode = ctxt->mode;
+	unsigned long modrm_ea;
+	int use_modrm_ea, scale, rip_relative = 0;
+	int no_wb = 0;
+	u64 msr_data, inst;
+	struct x86_prefix prefix;
+	int count;
+
+	/* Shadow copy of register state. Committed on successful emulation. */
+	unsigned long _regs[NR_VCPU_REGS];
+	unsigned long _eip = ctxt->vcpu->rip, _eflags = ctxt->eflags;
+	unsigned long modrm_val = 0;
+
+	memcpy(_regs, ctxt->vcpu->regs, sizeof _regs);
+
+	/* decode prefixes */
+
+	rc = ops->read_std(_eip + ctxt->base[X86EMUL_BASE_CS],
+			   &inst, sizeof(inst), ctxt->vcpu);
+	if ( rc != 0 )
+		goto done;
+
+	memset(&prefix, 0, sizeof(prefix));
+	prefix.override_base = -1;
+
+	count = x86_decode_prefix(mode, (u8*)&inst, &prefix);
+	if (count == -1)
+		return -1;
+	_eip += count;
+	b = insn_fetch(u8, 1, _eip);
+
 	/* Opcode byte(s). */
 	d = opcode_table[b];
 	if (d == 0) {
Index: kvm/drivers/kvm/x86_emulate.h
===================================================================
--- kvm.orig/drivers/kvm/x86_emulate.h	2007-07-31 18:00:51.000000000 +0200
+++ kvm/drivers/kvm/x86_emulate.h	2007-07-31 18:01:53.000000000 +0200
@@ -164,6 +164,13 @@
 #endif
 
 /*
+ * x86_decode_prefix: Decode instruction prefixes
+ * Returns -1 on failure, 0 on success.
+ */
+int
+x86_decode_prefix(int mode, u8 *inst, struct x86_prefix *prefix);
+
+/*
  * x86_emulate_memop: Emulate an instruction that faulted attempting to
  *                    read/write a 'special' memory area.
  * Returns -1 on failure, 0 on success.

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