powerpc: Change analyse_instr so it doesn't modify *regs

The analyse_instr function currently doesn't just work out what an
instruction does, it also executes those instructions whose effect
is only to update CPU registers that are stored in struct pt_regs.
This is undesirable because optprobes uses analyse_instr to work out
if an instruction could be successfully emulated in future.

This changes analyse_instr so it doesn't modify *regs; instead it
stores information in the instruction_op structure to indicate what
registers (GPRs, CR, XER, LR) would be set and what value they would
be set to.  A companion function called emulate_update_regs() can
then use that information to update a pt_regs struct appropriately.

As a minor cleanup, this replaces inline asm using the cntlzw and
cntlzd instructions with calls to __builtin_clz() and __builtin_clzl().

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/sstep.h

@@ -23,9 +23,6 @@ struct pt_regs;
 #define IS_RFID(instr)		(((instr) & 0xfc0007fe) == 0x4c000024)
 #define IS_RFI(instr)		(((instr) & 0xfc0007fe) == 0x4c000064)
 
-/* Emulate instructions that cause a transfer of control. */
-extern int emulate_step(struct pt_regs *regs, unsigned int instr);
-
 enum instruction_type {
 	COMPUTE,		/* arith/logical/CR op, etc. */
 	LOAD,
@@ -55,11 +52,29 @@ enum instruction_type {
 
 #define INSTR_TYPE_MASK	0x1f
 
+/* Compute flags, ORed in with type */
+#define SETREG		0x20
+#define SETCC		0x40
+#define SETXER		0x80
+
+/* Branch flags, ORed in with type */
+#define SETLK		0x20
+#define BRTAKEN		0x40
+#define DECCTR		0x80
+
 /* Load/store flags, ORed in with type */
 #define SIGNEXT		0x20
 #define UPDATE		0x40	/* matches bit in opcode 31 instructions */
 #define BYTEREV		0x80
 
+/* Barrier type field, ORed in with type */
+#define BARRIER_MASK	0xe0
+#define BARRIER_SYNC	0x00
+#define BARRIER_ISYNC	0x20
+#define BARRIER_EIEIO	0x40
+#define BARRIER_LWSYNC	0x60
+#define BARRIER_PTESYNC	0x80
+
 /* Cacheop values, ORed in with type */
 #define CACHEOP_MASK	0x700
 #define DCBST		0
@@ -83,7 +98,36 @@ struct instruction_op {
 	int update_reg;
 	/* For MFSPR */
 	int spr;
+	u32 ccval;
+	u32 xerval;
 };
 
-extern int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
+/*
+ * Decode an instruction, and return information about it in *op
+ * without changing *regs.
+ *
+ * Return value is 1 if the instruction can be emulated just by
+ * updating *regs with the information in *op, -1 if we need the
+ * GPRs but *regs doesn't contain the full register set, or 0
+ * otherwise.
+ */
+extern int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 			 unsigned int instr);
+
+/*
+ * Emulate an instruction that can be executed just by updating
+ * fields in *regs.
+ */
+void emulate_update_regs(struct pt_regs *reg, struct instruction_op *op);
+
+/*
+ * Emulate instructions that cause a transfer of control,
+ * arithmetic/logical instructions, loads and stores,
+ * cache operations and barriers.
+ *
+ * Returns 1 if the instruction was emulated successfully,
+ * 0 if it could not be emulated, or -1 for an instruction that
+ * should not be emulated (rfid, mtmsrd clearing MSR_RI, etc.).
+ */
+extern int emulate_step(struct pt_regs *regs, unsigned int instr);
+

arch/powerpc/lib/sstep.c

@@ -62,15 +62,17 @@ static nokprobe_inline unsigned long truncate_if_32bit(unsigned long msr,
 /*
  * Determine whether a conditional branch instruction would branch.
  */
-static nokprobe_inline int branch_taken(unsigned int instr, struct pt_regs *regs)
+static nokprobe_inline int branch_taken(unsigned int instr,
+					const struct pt_regs *regs,
+					struct instruction_op *op)
 {
 	unsigned int bo = (instr >> 21) & 0x1f;
 	unsigned int bi;
 
 	if ((bo & 4) == 0) {
 		/* decrement counter */
-		--regs->ctr;
-		if (((bo >> 1) & 1) ^ (regs->ctr == 0))
+		op->type |= DECCTR;
+		if (((bo >> 1) & 1) ^ (regs->ctr == 1))
 			return 0;
 	}
 	if ((bo & 0x10) == 0) {
@@ -92,7 +94,8 @@ static nokprobe_inline long address_ok(struct pt_regs *regs, unsigned long ea, i
 /*
  * Calculate effective address for a D-form instruction
  */
-static nokprobe_inline unsigned long dform_ea(unsigned int instr, struct pt_regs *regs)
+static nokprobe_inline unsigned long dform_ea(unsigned int instr,
+					      const struct pt_regs *regs)
 {
 	int ra;
 	unsigned long ea;
@@ -109,7 +112,8 @@ static nokprobe_inline unsigned long dform_ea(unsigned int instr, struct pt_regs
 /*
  * Calculate effective address for a DS-form instruction
  */
-static nokprobe_inline unsigned long dsform_ea(unsigned int instr, struct pt_regs *regs)
+static nokprobe_inline unsigned long dsform_ea(unsigned int instr,
+					       const struct pt_regs *regs)
 {
 	int ra;
 	unsigned long ea;
@@ -127,7 +131,7 @@ static nokprobe_inline unsigned long dsform_ea(unsigned int instr, struct pt_reg
  * Calculate effective address for an X-form instruction
  */
 static nokprobe_inline unsigned long xform_ea(unsigned int instr,
-						struct pt_regs *regs)
+					      const struct pt_regs *regs)
 {
 	int ra, rb;
 	unsigned long ea;
@@ -526,24 +530,27 @@ static nokprobe_inline int do_vsx_store(int rn, int (*func)(int, unsigned long),
 		: "=r" (err)				\
 		: "r" (addr), "i" (-EFAULT), "0" (err))
 
-static nokprobe_inline void set_cr0(struct pt_regs *regs, int rd)
+static nokprobe_inline void set_cr0(const struct pt_regs *regs,
+				    struct instruction_op *op, int rd)
 {
 	long val = regs->gpr[rd];
 
-	regs->ccr = (regs->ccr & 0x0fffffff) | ((regs->xer >> 3) & 0x10000000);
+	op->type |= SETCC;
+	op->ccval = (regs->ccr & 0x0fffffff) | ((regs->xer >> 3) & 0x10000000);
 #ifdef __powerpc64__
 	if (!(regs->msr & MSR_64BIT))
 		val = (int) val;
 #endif
 	if (val < 0)
-		regs->ccr |= 0x80000000;
+		op->ccval |= 0x80000000;
 	else if (val > 0)
-		regs->ccr |= 0x40000000;
+		op->ccval |= 0x40000000;
 	else
-		regs->ccr |= 0x20000000;
+		op->ccval |= 0x20000000;
 }
 
-static nokprobe_inline void add_with_carry(struct pt_regs *regs, int rd,
+static nokprobe_inline void add_with_carry(const struct pt_regs *regs,
+				     struct instruction_op *op, int rd,
 				     unsigned long val1, unsigned long val2,
 				     unsigned long carry_in)
 {
@@ -551,24 +558,29 @@ static nokprobe_inline void add_with_carry(struct pt_regs *regs, int rd,
 
 	if (carry_in)
 		++val;
-	regs->gpr[rd] = val;
+	op->type = COMPUTE + SETREG + SETXER;
+	op->reg = rd;
+	op->val = val;
 #ifdef __powerpc64__
 	if (!(regs->msr & MSR_64BIT)) {
 		val = (unsigned int) val;
 		val1 = (unsigned int) val1;
 	}
 #endif
+	op->xerval = regs->xer;
 	if (val < val1 || (carry_in && val == val1))
-		regs->xer |= XER_CA;
+		op->xerval |= XER_CA;
 	else
-		regs->xer &= ~XER_CA;
+		op->xerval &= ~XER_CA;
 }
 
-static nokprobe_inline void do_cmp_signed(struct pt_regs *regs, long v1, long v2,
-				    int crfld)
+static nokprobe_inline void do_cmp_signed(const struct pt_regs *regs,
+					  struct instruction_op *op,
+					  long v1, long v2, int crfld)
 {
 	unsigned int crval, shift;
 
+	op->type = COMPUTE + SETCC;
 	crval = (regs->xer >> 31) & 1;		/* get SO bit */
 	if (v1 < v2)
 		crval |= 8;
@@ -577,14 +589,17 @@ static nokprobe_inline void do_cmp_signed(struct pt_regs *regs, long v1, long v2
 	else
 		crval |= 2;
 	shift = (7 - crfld) * 4;
-	regs->ccr = (regs->ccr & ~(0xf << shift)) | (crval << shift);
+	op->ccval = (regs->ccr & ~(0xf << shift)) | (crval << shift);
 }
 
-static nokprobe_inline void do_cmp_unsigned(struct pt_regs *regs, unsigned long v1,
-				      unsigned long v2, int crfld)
+static nokprobe_inline void do_cmp_unsigned(const struct pt_regs *regs,
+					    struct instruction_op *op,
+					    unsigned long v1,
+					    unsigned long v2, int crfld)
 {
 	unsigned int crval, shift;
 
+	op->type = COMPUTE + SETCC;
 	crval = (regs->xer >> 31) & 1;		/* get SO bit */
 	if (v1 < v2)
 		crval |= 8;
@@ -593,11 +608,12 @@ static nokprobe_inline void do_cmp_unsigned(struct pt_regs *regs, unsigned long
 	else
 		crval |= 2;
 	shift = (7 - crfld) * 4;
-	regs->ccr = (regs->ccr & ~(0xf << shift)) | (crval << shift);
+	op->ccval = (regs->ccr & ~(0xf << shift)) | (crval << shift);
 }
 
-static nokprobe_inline void do_cmpb(struct pt_regs *regs, unsigned long v1,
-				unsigned long v2, int rd)
+static nokprobe_inline void do_cmpb(const struct pt_regs *regs,
+				    struct instruction_op *op,
+				    unsigned long v1, unsigned long v2)
 {
 	unsigned long long out_val, mask;
 	int i;
@@ -608,16 +624,16 @@ static nokprobe_inline void do_cmpb(struct pt_regs *regs, unsigned long v1,
 		if ((v1 & mask) == (v2 & mask))
 			out_val |= mask;
 	}
-
-	regs->gpr[rd] = out_val;
+	op->val = out_val;
 }
 
 /*
  * The size parameter is used to adjust the equivalent popcnt instruction.
  * popcntb = 8, popcntw = 32, popcntd = 64
  */
-static nokprobe_inline void do_popcnt(struct pt_regs *regs, unsigned long v1,
-				int size, int ra)
+static nokprobe_inline void do_popcnt(const struct pt_regs *regs,
+				      struct instruction_op *op,
+				      unsigned long v1, int size)
 {
 	unsigned long long out = v1;
 
@@ -626,23 +642,24 @@ static nokprobe_inline void do_popcnt(struct pt_regs *regs, unsigned long v1,
 	out = (out + (out >> 4)) & 0x0f0f0f0f0f0f0f0f;
 
 	if (size == 8) {	/* popcntb */
-		regs->gpr[ra] = out;
+		op->val = out;
 		return;
 	}
 	out += out >> 8;
 	out += out >> 16;
 	if (size == 32) {	/* popcntw */
-		regs->gpr[ra] = out & 0x0000003f0000003f;
+		op->val = out & 0x0000003f0000003f;
 		return;
 	}
 
 	out = (out + (out >> 32)) & 0x7f;
-	regs->gpr[ra] = out;	/* popcntd */
+	op->val = out;	/* popcntd */
 }
 
 #ifdef CONFIG_PPC64
-static nokprobe_inline void do_bpermd(struct pt_regs *regs, unsigned long v1,
-				unsigned long v2, int ra)
+static nokprobe_inline void do_bpermd(const struct pt_regs *regs,
+				      struct instruction_op *op,
+				      unsigned long v1, unsigned long v2)
 {
 	unsigned char perm, idx;
 	unsigned int i;
@@ -654,26 +671,27 @@ static nokprobe_inline void do_bpermd(struct pt_regs *regs, unsigned long v1,
 			if (v2 & PPC_BIT(idx))
 				perm |= 1 << i;
 	}
-	regs->gpr[ra] = perm;
+	op->val = perm;
 }
 #endif /* CONFIG_PPC64 */
 /*
  * The size parameter adjusts the equivalent prty instruction.
  * prtyw = 32, prtyd = 64
  */
-static nokprobe_inline void do_prty(struct pt_regs *regs, unsigned long v,
-				int size, int ra)
+static nokprobe_inline void do_prty(const struct pt_regs *regs,
+				    struct instruction_op *op,
+				    unsigned long v, int size)
 {
 	unsigned long long res = v ^ (v >> 8);
 
 	res ^= res >> 16;
 	if (size == 32) {		/* prtyw */
-		regs->gpr[ra] = res & 0x0000000100000001;
+		op->val = res & 0x0000000100000001;
 		return;
 	}
 
 	res ^= res >> 32;
-	regs->gpr[ra] = res & 1;	/*prtyd */
+	op->val = res & 1;	/*prtyd */
 }
 
 static nokprobe_inline int trap_compare(long v1, long v2)
@@ -709,14 +727,18 @@ static nokprobe_inline int trap_compare(long v1, long v2)
 #define ROTATE(x, n)	((n) ? (((x) << (n)) | ((x) >> (8 * sizeof(long) - (n)))) : (x))
 
 /*
- * Decode an instruction, and execute it if that can be done just by
- * modifying *regs (i.e. integer arithmetic and logical instructions,
- * branches, and barrier instructions).
- * Returns 1 if the instruction has been executed, or 0 if not.
- * Sets *op to indicate what the instruction does.
+ * Decode an instruction, and return information about it in *op
+ * without changing *regs.
+ * Integer arithmetic and logical instructions, branches, and barrier
+ * instructions can be emulated just using the information in *op.
+ *
+ * Return value is 1 if the instruction can be emulated just by
+ * updating *regs with the information in *op, -1 if we need the
+ * GPRs but *regs doesn't contain the full register set, or 0
+ * otherwise.
  */
-int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
-			    unsigned int instr)
+int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
+		  unsigned int instr)
 {
 	unsigned int opcode, ra, rb, rd, spr, u;
 	unsigned long int imm;
@@ -733,12 +755,11 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		imm = (signed short)(instr & 0xfffc);
 		if ((instr & 2) == 0)
 			imm += regs->nip;
-		regs->nip += 4;
-		regs->nip = truncate_if_32bit(regs->msr, regs->nip);
+		op->val = truncate_if_32bit(regs->msr, imm);
 		if (instr & 1)
-			regs->link = regs->nip;
-		if (branch_taken(instr, regs))
-			regs->nip = truncate_if_32bit(regs->msr, imm);
+			op->type |= SETLK;
+		if (branch_taken(instr, regs, op))
+			op->type |= BRTAKEN;
 		return 1;
 #ifdef CONFIG_PPC64
 	case 17:	/* sc */
@@ -749,38 +770,37 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		return 0;
 #endif
 	case 18:	/* b */
-		op->type = BRANCH;
+		op->type = BRANCH | BRTAKEN;
 		imm = instr & 0x03fffffc;
 		if (imm & 0x02000000)
 			imm -= 0x04000000;
 		if ((instr & 2) == 0)
 			imm += regs->nip;
+		op->val = truncate_if_32bit(regs->msr, imm);
 		if (instr & 1)
-			regs->link = truncate_if_32bit(regs->msr, regs->nip + 4);
-		imm = truncate_if_32bit(regs->msr, imm);
-		regs->nip = imm;
+			op->type |= SETLK;
 		return 1;
 	case 19:
 		switch ((instr >> 1) & 0x3ff) {
 		case 0:		/* mcrf */
+			op->type = COMPUTE + SETCC;
 			rd = 7 - ((instr >> 23) & 0x7);
 			ra = 7 - ((instr >> 18) & 0x7);
 			rd *= 4;
 			ra *= 4;
 			val = (regs->ccr >> ra) & 0xf;
-			regs->ccr = (regs->ccr & ~(0xfUL << rd)) | (val << rd);
-			goto instr_done;
+			op->ccval = (regs->ccr & ~(0xfUL << rd)) | (val << rd);
+			return 1;
 
 		case 16:	/* bclr */
 		case 528:	/* bcctr */
 			op->type = BRANCH;
 			imm = (instr & 0x400)? regs->ctr: regs->link;
-			regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
-			imm = truncate_if_32bit(regs->msr, imm);
+			op->val = truncate_if_32bit(regs->msr, imm);
 			if (instr & 1)
-				regs->link = regs->nip;
-			if (branch_taken(instr, regs))
-				regs->nip = imm;
+				op->type |= SETLK;
+			if (branch_taken(instr, regs, op))
+				op->type |= BRTAKEN;
 			return 1;
 
 		case 18:	/* rfid, scary */
@@ -790,9 +810,8 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 			return 0;
 
 		case 150:	/* isync */
-			op->type = BARRIER;
-			isync();
-			goto instr_done;
+			op->type = BARRIER | BARRIER_ISYNC;
+			return 1;
 
 		case 33:	/* crnor */
 		case 129:	/* crandc */
@@ -802,45 +821,47 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		case 289:	/* creqv */
 		case 417:	/* crorc */
 		case 449:	/* cror */
+			op->type = COMPUTE + SETCC;
 			ra = (instr >> 16) & 0x1f;
 			rb = (instr >> 11) & 0x1f;
 			rd = (instr >> 21) & 0x1f;
 			ra = (regs->ccr >> (31 - ra)) & 1;
 			rb = (regs->ccr >> (31 - rb)) & 1;
 			val = (instr >> (6 + ra * 2 + rb)) & 1;
-			regs->ccr = (regs->ccr & ~(1UL << (31 - rd))) |
+			op->ccval = (regs->ccr & ~(1UL << (31 - rd))) |
 				(val << (31 - rd));
-			goto instr_done;
+			return 1;
+		default:
+			op->type = UNKNOWN;
+			return 0;
 		}
 		break;
 	case 31:
 		switch ((instr >> 1) & 0x3ff) {
 		case 598:	/* sync */
-			op->type = BARRIER;
+			op->type = BARRIER + BARRIER_SYNC;
 #ifdef __powerpc64__
 			switch ((instr >> 21) & 3) {
 			case 1:		/* lwsync */
-				asm volatile("lwsync" : : : "memory");
-				goto instr_done;
+				op->type = BARRIER + BARRIER_LWSYNC;
+				break;
 			case 2:		/* ptesync */
-				asm volatile("ptesync" : : : "memory");
-				goto instr_done;
+				op->type = BARRIER + BARRIER_PTESYNC;
+				break;
 			}
 #endif
-			mb();
-			goto instr_done;
+			return 1;
 
 		case 854:	/* eieio */
-			op->type = BARRIER;
-			eieio();
-			goto instr_done;
+			op->type = BARRIER + BARRIER_EIEIO;
+			return 1;
 		}
 		break;
 	}
 
 	/* Following cases refer to regs->gpr[], so we need all regs */
 	if (!FULL_REGS(regs))
-		return 0;
+		return -1;
 
 	rd = (instr >> 21) & 0x1f;
 	ra = (instr >> 16) & 0x1f;
@@ -851,21 +872,21 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 	case 2:		/* tdi */
 		if (rd & trap_compare(regs->gpr[ra], (short) instr))
 			goto trap;
-		goto instr_done;
+		return 1;
 #endif
 	case 3:		/* twi */
 		if (rd & trap_compare((int)regs->gpr[ra], (short) instr))
 			goto trap;
-		goto instr_done;
+		return 1;
 
 	case 7:		/* mulli */
-		regs->gpr[rd] = regs->gpr[ra] * (short) instr;
-		goto instr_done;
+		op->val = regs->gpr[ra] * (short) instr;
+		goto compute_done;
 
 	case 8:		/* subfic */
 		imm = (short) instr;
-		add_with_carry(regs, rd, ~regs->gpr[ra], imm, 1);
-		goto instr_done;
+		add_with_carry(regs, op, rd, ~regs->gpr[ra], imm, 1);
+		return 1;
 
 	case 10:	/* cmpli */
 		imm = (unsigned short) instr;
@@ -874,8 +895,8 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		if ((rd & 1) == 0)
 			val = (unsigned int) val;
 #endif
-		do_cmp_unsigned(regs, val, imm, rd >> 2);
-		goto instr_done;
+		do_cmp_unsigned(regs, op, val, imm, rd >> 2);
+		return 1;
 
 	case 11:	/* cmpi */
 		imm = (short) instr;
@@ -884,47 +905,47 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		if ((rd & 1) == 0)
 			val = (int) val;
 #endif
-		do_cmp_signed(regs, val, imm, rd >> 2);
-		goto instr_done;
+		do_cmp_signed(regs, op, val, imm, rd >> 2);
+		return 1;
 
 	case 12:	/* addic */
 		imm = (short) instr;
-		add_with_carry(regs, rd, regs->gpr[ra], imm, 0);
-		goto instr_done;
+		add_with_carry(regs, op, rd, regs->gpr[ra], imm, 0);
+		return 1;
 
 	case 13:	/* addic. */
 		imm = (short) instr;
-		add_with_carry(regs, rd, regs->gpr[ra], imm, 0);
-		set_cr0(regs, rd);
-		goto instr_done;
+		add_with_carry(regs, op, rd, regs->gpr[ra], imm, 0);
+		set_cr0(regs, op, rd);
+		return 1;
 
 	case 14:	/* addi */
 		imm = (short) instr;
 		if (ra)
 			imm += regs->gpr[ra];
-		regs->gpr[rd] = imm;
-		goto instr_done;
+		op->val = imm;
+		goto compute_done;
 
 	case 15:	/* addis */
 		imm = ((short) instr) << 16;
 		if (ra)
 			imm += regs->gpr[ra];
-		regs->gpr[rd] = imm;
-		goto instr_done;
+		op->val = imm;
+		goto compute_done;
 
 	case 20:	/* rlwimi */
 		mb = (instr >> 6) & 0x1f;
 		me = (instr >> 1) & 0x1f;
 		val = DATA32(regs->gpr[rd]);
 		imm = MASK32(mb, me);
-		regs->gpr[ra] = (regs->gpr[ra] & ~imm) | (ROTATE(val, rb) & imm);
+		op->val = (regs->gpr[ra] & ~imm) | (ROTATE(val, rb) & imm);
 		goto logical_done;
 
 	case 21:	/* rlwinm */
 		mb = (instr >> 6) & 0x1f;
 		me = (instr >> 1) & 0x1f;
 		val = DATA32(regs->gpr[rd]);
-		regs->gpr[ra] = ROTATE(val, rb) & MASK32(mb, me);
+		op->val = ROTATE(val, rb) & MASK32(mb, me);
 		goto logical_done;
 
 	case 23:	/* rlwnm */
@@ -932,40 +953,37 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		me = (instr >> 1) & 0x1f;
 		rb = regs->gpr[rb] & 0x1f;
 		val = DATA32(regs->gpr[rd]);
-		regs->gpr[ra] = ROTATE(val, rb) & MASK32(mb, me);
+		op->val = ROTATE(val, rb) & MASK32(mb, me);
 		goto logical_done;
 
 	case 24:	/* ori */
-		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] | imm;
-		goto instr_done;
+		op->val = regs->gpr[rd] | (unsigned short) instr;
+		goto logical_done_nocc;
 
 	case 25:	/* oris */
 		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] | (imm << 16);
-		goto instr_done;
+		op->val = regs->gpr[rd] | (imm << 16);
+		goto logical_done_nocc;
 
 	case 26:	/* xori */
-		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] ^ imm;
-		goto instr_done;
+		op->val = regs->gpr[rd] ^ (unsigned short) instr;
+		goto logical_done_nocc;
 
 	case 27:	/* xoris */
 		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] ^ (imm << 16);
-		goto instr_done;
+		op->val = regs->gpr[rd] ^ (imm << 16);
+		goto logical_done_nocc;
 
 	case 28:	/* andi. */
-		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] & imm;
-		set_cr0(regs, ra);
-		goto instr_done;
+		op->val = regs->gpr[rd] & (unsigned short) instr;
+		set_cr0(regs, op, ra);
+		goto logical_done_nocc;
 
 	case 29:	/* andis. */
 		imm = (unsigned short) instr;
-		regs->gpr[ra] = regs->gpr[rd] & (imm << 16);
-		set_cr0(regs, ra);
-		goto instr_done;
+		op->val = regs->gpr[rd] & (imm << 16);
+		set_cr0(regs, op, ra);
+		goto logical_done_nocc;
 
 #ifdef __powerpc64__
 	case 30:	/* rld* */
@@ -976,34 +994,36 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 			val = ROTATE(val, sh);
 			switch ((instr >> 2) & 3) {
 			case 0:		/* rldicl */
-				regs->gpr[ra] = val & MASK64_L(mb);
-				goto logical_done;
+				val &= MASK64_L(mb);
+				break;
 			case 1:		/* rldicr */
-				regs->gpr[ra] = val & MASK64_R(mb);
-				goto logical_done;
+				val &= MASK64_R(mb);
+				break;
 			case 2:		/* rldic */
-				regs->gpr[ra] = val & MASK64(mb, 63 - sh);
-				goto logical_done;
+				val &= MASK64(mb, 63 - sh);
+				break;
 			case 3:		/* rldimi */
 				imm = MASK64(mb, 63 - sh);
-				regs->gpr[ra] = (regs->gpr[ra] & ~imm) |
+				val = (regs->gpr[ra] & ~imm) |
 					(val & imm);
-				goto logical_done;
 			}
+			op->val = val;
+			goto logical_done;
 		} else {
 			sh = regs->gpr[rb] & 0x3f;
 			val = ROTATE(val, sh);
 			switch ((instr >> 1) & 7) {
 			case 0:		/* rldcl */
-				regs->gpr[ra] = val & MASK64_L(mb);
+				op->val = val & MASK64_L(mb);
 				goto logical_done;
 			case 1:		/* rldcr */
-				regs->gpr[ra] = val & MASK64_R(mb);
+				op->val = val & MASK64_R(mb);
 				goto logical_done;
 			}
 		}
 #endif
-	break; /* illegal instruction */
+		op->type = UNKNOWN;	/* illegal instruction */
+		return 0;
 
 	case 31:
 		switch ((instr >> 1) & 0x3ff) {
@@ -1012,12 +1032,12 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 			    (rd & trap_compare((int)regs->gpr[ra],
 					       (int)regs->gpr[rb])))
 				goto trap;
-			goto instr_done;
+			return 1;
 #ifdef __powerpc64__
 		case 68:	/* td */
 			if (rd & trap_compare(regs->gpr[ra], regs->gpr[rb]))
 				goto trap;
-			goto instr_done;
+			return 1;
 #endif
 		case 83:	/* mfmsr */
 			if (regs->msr & MSR_PR)
@@ -1046,74 +1066,50 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 #endif
 
 		case 19:	/* mfcr */
+			imm = 0xffffffffUL;
 			if ((instr >> 20) & 1) {
 				imm = 0xf0000000UL;
 				for (sh = 0; sh < 8; ++sh) {
-					if (instr & (0x80000 >> sh)) {
-						regs->gpr[rd] = regs->ccr & imm;
+					if (instr & (0x80000 >> sh))
 						break;
-					}
 					imm >>= 4;
 				}
-
-				goto instr_done;
 			}
-
-			regs->gpr[rd] = regs->ccr;
-			regs->gpr[rd] &= 0xffffffffUL;
-			goto instr_done;
+			op->val = regs->ccr & imm;
+			goto compute_done;
 
 		case 144:	/* mtcrf */
+			op->type = COMPUTE + SETCC;
 			imm = 0xf0000000UL;
 			val = regs->gpr[rd];
+			op->val = regs->ccr;
 			for (sh = 0; sh < 8; ++sh) {
 				if (instr & (0x80000 >> sh))
-					regs->ccr = (regs->ccr & ~imm) |
+					op->val = (op->val & ~imm) |
 						(val & imm);
 				imm >>= 4;
 			}
-			goto instr_done;
+			return 1;
 
 		case 339:	/* mfspr */
 			spr = ((instr >> 16) & 0x1f) | ((instr >> 6) & 0x3e0);
-			switch (spr) {
-			case SPRN_XER:	/* mfxer */
-				regs->gpr[rd] = regs->xer;
-				regs->gpr[rd] &= 0xffffffffUL;
-				goto instr_done;
-			case SPRN_LR:	/* mflr */
-				regs->gpr[rd] = regs->link;
-				goto instr_done;
-			case SPRN_CTR:	/* mfctr */
-				regs->gpr[rd] = regs->ctr;
-				goto instr_done;
-			default:
-				op->type = MFSPR;
-				op->reg = rd;
-				op->spr = spr;
-				return 0;
-			}
-			break;
+			op->type = MFSPR;
+			op->reg = rd;
+			op->spr = spr;
+			if (spr == SPRN_XER || spr == SPRN_LR ||
+			    spr == SPRN_CTR)
+				return 1;
+			return 0;
 
 		case 467:	/* mtspr */
 			spr = ((instr >> 16) & 0x1f) | ((instr >> 6) & 0x3e0);
-			switch (spr) {
-			case SPRN_XER:	/* mtxer */
-				regs->xer = (regs->gpr[rd] & 0xffffffffUL);
-				goto instr_done;
-			case SPRN_LR:	/* mtlr */
-				regs->link = regs->gpr[rd];
-				goto instr_done;
-			case SPRN_CTR:	/* mtctr */
-				regs->ctr = regs->gpr[rd];
-				goto instr_done;
-			default:
-				op->type = MTSPR;
-				op->val = regs->gpr[rd];
-				op->spr = spr;
-				return 0;
-			}
-			break;
+			op->type = MTSPR;
+			op->val = regs->gpr[rd];
+			op->spr = spr;
+			if (spr == SPRN_XER || spr == SPRN_LR ||
+			    spr == SPRN_CTR)
+				return 1;
+			return 0;
 
 /*
  * Compare instructions
@@ -1128,8 +1124,8 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 				val2 = (int) val2;
 			}
 #endif
-			do_cmp_signed(regs, val, val2, rd >> 2);
-			goto instr_done;
+			do_cmp_signed(regs, op, val, val2, rd >> 2);
+			return 1;
 
 		case 32:	/* cmpl */
 			val = regs->gpr[ra];
@@ -1141,113 +1137,113 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 				val2 = (unsigned int) val2;
 			}
 #endif
-			do_cmp_unsigned(regs, val, val2, rd >> 2);
-			goto instr_done;
+			do_cmp_unsigned(regs, op, val, val2, rd >> 2);
+			return 1;
 
 		case 508: /* cmpb */
-			do_cmpb(regs, regs->gpr[rd], regs->gpr[rb], ra);
-			goto instr_done;
+			do_cmpb(regs, op, regs->gpr[rd], regs->gpr[rb]);
+			goto logical_done_nocc;
 
 /*
  * Arithmetic instructions
  */
 		case 8:	/* subfc */
-			add_with_carry(regs, rd, ~regs->gpr[ra],
+			add_with_carry(regs, op, rd, ~regs->gpr[ra],
 				       regs->gpr[rb], 1);
 			goto arith_done;
 #ifdef __powerpc64__
 		case 9:	/* mulhdu */
-			asm("mulhdu %0,%1,%2" : "=r" (regs->gpr[rd]) :
+			asm("mulhdu %0,%1,%2" : "=r" (op->val) :
 			    "r" (regs->gpr[ra]), "r" (regs->gpr[rb]));
 			goto arith_done;
 #endif
 		case 10:	/* addc */
-			add_with_carry(regs, rd, regs->gpr[ra],
+			add_with_carry(regs, op, rd, regs->gpr[ra],
 				       regs->gpr[rb], 0);
 			goto arith_done;
 
 		case 11:	/* mulhwu */
-			asm("mulhwu %0,%1,%2" : "=r" (regs->gpr[rd]) :
+			asm("mulhwu %0,%1,%2" : "=r" (op->val) :
 			    "r" (regs->gpr[ra]), "r" (regs->gpr[rb]));
 			goto arith_done;
 
 		case 40:	/* subf */
-			regs->gpr[rd] = regs->gpr[rb] - regs->gpr[ra];
+			op->val = regs->gpr[rb] - regs->gpr[ra];
 			goto arith_done;
 #ifdef __powerpc64__
 		case 73:	/* mulhd */
-			asm("mulhd %0,%1,%2" : "=r" (regs->gpr[rd]) :
+			asm("mulhd %0,%1,%2" : "=r" (op->val) :
 			    "r" (regs->gpr[ra]), "r" (regs->gpr[rb]));
 			goto arith_done;
 #endif
 		case 75:	/* mulhw */
-			asm("mulhw %0,%1,%2" : "=r" (regs->gpr[rd]) :
+			asm("mulhw %0,%1,%2" : "=r" (op->val) :
 			    "r" (regs->gpr[ra]), "r" (regs->gpr[rb]));
 			goto arith_done;
 
 		case 104:	/* neg */
-			regs->gpr[rd] = -regs->gpr[ra];
+			op->val = -regs->gpr[ra];
 			goto arith_done;
 
 		case 136:	/* subfe */
-			add_with_carry(regs, rd, ~regs->gpr[ra], regs->gpr[rb],
-				       regs->xer & XER_CA);
+			add_with_carry(regs, op, rd, ~regs->gpr[ra],
+				       regs->gpr[rb], regs->xer & XER_CA);
 			goto arith_done;
 
 		case 138:	/* adde */
-			add_with_carry(regs, rd, regs->gpr[ra], regs->gpr[rb],
-				       regs->xer & XER_CA);
+			add_with_carry(regs, op, rd, regs->gpr[ra],
+				       regs->gpr[rb], regs->xer & XER_CA);
 			goto arith_done;
 
 		case 200:	/* subfze */
-			add_with_carry(regs, rd, ~regs->gpr[ra], 0L,
+			add_with_carry(regs, op, rd, ~regs->gpr[ra], 0L,
 				       regs->xer & XER_CA);
 			goto arith_done;
 
 		case 202:	/* addze */
-			add_with_carry(regs, rd, regs->gpr[ra], 0L,
+			add_with_carry(regs, op, rd, regs->gpr[ra], 0L,
 				       regs->xer & XER_CA);
 			goto arith_done;
 
 		case 232:	/* subfme */
-			add_with_carry(regs, rd, ~regs->gpr[ra], -1L,
+			add_with_carry(regs, op, rd, ~regs->gpr[ra], -1L,
 				       regs->xer & XER_CA);
 			goto arith_done;
 #ifdef __powerpc64__
 		case 233:	/* mulld */
-			regs->gpr[rd] = regs->gpr[ra] * regs->gpr[rb];
+			op->val = regs->gpr[ra] * regs->gpr[rb];
 			goto arith_done;
 #endif
 		case 234:	/* addme */
-			add_with_carry(regs, rd, regs->gpr[ra], -1L,
+			add_with_carry(regs, op, rd, regs->gpr[ra], -1L,
 				       regs->xer & XER_CA);
 			goto arith_done;
 
 		case 235:	/* mullw */
-			regs->gpr[rd] = (unsigned int) regs->gpr[ra] *
+			op->val = (unsigned int) regs->gpr[ra] *
 				(unsigned int) regs->gpr[rb];
 			goto arith_done;
 
 		case 266:	/* add */
-			regs->gpr[rd] = regs->gpr[ra] + regs->gpr[rb];
+			op->val = regs->gpr[ra] + regs->gpr[rb];
 			goto arith_done;
 #ifdef __powerpc64__
 		case 457:	/* divdu */
-			regs->gpr[rd] = regs->gpr[ra] / regs->gpr[rb];
+			op->val = regs->gpr[ra] / regs->gpr[rb];
 			goto arith_done;
 #endif
 		case 459:	/* divwu */
-			regs->gpr[rd] = (unsigned int) regs->gpr[ra] /
+			op->val = (unsigned int) regs->gpr[ra] /
 				(unsigned int) regs->gpr[rb];
 			goto arith_done;
 #ifdef __powerpc64__
 		case 489:	/* divd */
-			regs->gpr[rd] = (long int) regs->gpr[ra] /
+			op->val = (long int) regs->gpr[ra] /
 				(long int) regs->gpr[rb];
 			goto arith_done;
 #endif
 		case 491:	/* divw */
-			regs->gpr[rd] = (int) regs->gpr[ra] /
+			op->val = (int) regs->gpr[ra] /
 				(int) regs->gpr[rb];
 			goto arith_done;
 
@@ -1260,85 +1256,83 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 			val = (regs->ccr >> (31 - mb)) & 1;
 			val2 = (ra) ? regs->gpr[ra] : 0;
 
-			regs->gpr[rd] = (val) ? val2 : regs->gpr[rb];
-			goto logical_done;
+			op->val = (val) ? val2 : regs->gpr[rb];
+			goto compute_done;
 
 		case 26:	/* cntlzw */
-			asm("cntlzw %0,%1" : "=r" (regs->gpr[ra]) :
-			    "r" (regs->gpr[rd]));
+			op->val = __builtin_clz((unsigned int) regs->gpr[rd]);
 			goto logical_done;
 #ifdef __powerpc64__
 		case 58:	/* cntlzd */
-			asm("cntlzd %0,%1" : "=r" (regs->gpr[ra]) :
-			    "r" (regs->gpr[rd]));
+			op->val = __builtin_clzl(regs->gpr[rd]);
 			goto logical_done;
 #endif
 		case 28:	/* and */
-			regs->gpr[ra] = regs->gpr[rd] & regs->gpr[rb];
+			op->val = regs->gpr[rd] & regs->gpr[rb];
 			goto logical_done;
 
 		case 60:	/* andc */
-			regs->gpr[ra] = regs->gpr[rd] & ~regs->gpr[rb];
+			op->val = regs->gpr[rd] & ~regs->gpr[rb];
 			goto logical_done;
 
 		case 122:	/* popcntb */
-			do_popcnt(regs, regs->gpr[rd], 8, ra);
+			do_popcnt(regs, op, regs->gpr[rd], 8);
 			goto logical_done;
 
 		case 124:	/* nor */
-			regs->gpr[ra] = ~(regs->gpr[rd] | regs->gpr[rb]);
+			op->val = ~(regs->gpr[rd] | regs->gpr[rb]);
 			goto logical_done;
 
 		case 154:	/* prtyw */
-			do_prty(regs, regs->gpr[rd], 32, ra);
+			do_prty(regs, op, regs->gpr[rd], 32);
 			goto logical_done;
 
 		case 186:	/* prtyd */
-			do_prty(regs, regs->gpr[rd], 64, ra);
+			do_prty(regs, op, regs->gpr[rd], 64);
 			goto logical_done;
 #ifdef CONFIG_PPC64
 		case 252:	/* bpermd */
-			do_bpermd(regs, regs->gpr[rd], regs->gpr[rb], ra);
+			do_bpermd(regs, op, regs->gpr[rd], regs->gpr[rb]);
 			goto logical_done;
 #endif
 		case 284:	/* xor */
-			regs->gpr[ra] = ~(regs->gpr[rd] ^ regs->gpr[rb]);
+			op->val = ~(regs->gpr[rd] ^ regs->gpr[rb]);
 			goto logical_done;
 
 		case 316:	/* xor */
-			regs->gpr[ra] = regs->gpr[rd] ^ regs->gpr[rb];
+			op->val = regs->gpr[rd] ^ regs->gpr[rb];
 			goto logical_done;
 
 		case 378:	/* popcntw */
-			do_popcnt(regs, regs->gpr[rd], 32, ra);
+			do_popcnt(regs, op, regs->gpr[rd], 32);
 			goto logical_done;
 
 		case 412:	/* orc */
-			regs->gpr[ra] = regs->gpr[rd] | ~regs->gpr[rb];
+			op->val = regs->gpr[rd] | ~regs->gpr[rb];
 			goto logical_done;
 
 		case 444:	/* or */
-			regs->gpr[ra] = regs->gpr[rd] | regs->gpr[rb];
+			op->val = regs->gpr[rd] | regs->gpr[rb];
 			goto logical_done;
 
 		case 476:	/* nand */
-			regs->gpr[ra] = ~(regs->gpr[rd] & regs->gpr[rb]);
+			op->val = ~(regs->gpr[rd] & regs->gpr[rb]);
 			goto logical_done;
 #ifdef CONFIG_PPC64
 		case 506:	/* popcntd */
-			do_popcnt(regs, regs->gpr[rd], 64, ra);
+			do_popcnt(regs, op, regs->gpr[rd], 64);
 			goto logical_done;
 #endif
 		case 922:	/* extsh */
-			regs->gpr[ra] = (signed short) regs->gpr[rd];
+			op->val = (signed short) regs->gpr[rd];
 			goto logical_done;
 
 		case 954:	/* extsb */
-			regs->gpr[ra] = (signed char) regs->gpr[rd];
+			op->val = (signed char) regs->gpr[rd];
 			goto logical_done;
 #ifdef __powerpc64__
 		case 986:	/* extsw */
-			regs->gpr[ra] = (signed int) regs->gpr[rd];
+			op->val = (signed int) regs->gpr[rd];
 			goto logical_done;
 #endif
 
@@ -1348,75 +1342,83 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 		case 24:	/* slw */
 			sh = regs->gpr[rb] & 0x3f;
 			if (sh < 32)
-				regs->gpr[ra] = (regs->gpr[rd] << sh) & 0xffffffffUL;
+				op->val = (regs->gpr[rd] << sh) & 0xffffffffUL;
 			else
-				regs->gpr[ra] = 0;
+				op->val = 0;
 			goto logical_done;
 
 		case 536:	/* srw */
 			sh = regs->gpr[rb] & 0x3f;
 			if (sh < 32)
-				regs->gpr[ra] = (regs->gpr[rd] & 0xffffffffUL) >> sh;
+				op->val = (regs->gpr[rd] & 0xffffffffUL) >> sh;
 			else
-				regs->gpr[ra] = 0;
+				op->val = 0;
 			goto logical_done;
 
 		case 792:	/* sraw */
+			op->type = COMPUTE + SETREG + SETXER;
 			sh = regs->gpr[rb] & 0x3f;
 			ival = (signed int) regs->gpr[rd];
-			regs->gpr[ra] = ival >> (sh < 32 ? sh : 31);
+			op->val = ival >> (sh < 32 ? sh : 31);
+			op->xerval = regs->xer;
 			if (ival < 0 && (sh >= 32 || (ival & ((1ul << sh) - 1)) != 0))
-				regs->xer |= XER_CA;
+				op->xerval |= XER_CA;
 			else
-				regs->xer &= ~XER_CA;
+				op->xerval &= ~XER_CA;
 			goto logical_done;
 
 		case 824:	/* srawi */
+			op->type = COMPUTE + SETREG + SETXER;
 			sh = rb;
 			ival = (signed int) regs->gpr[rd];
-			regs->gpr[ra] = ival >> sh;
+			op->val = ival >> sh;
+			op->xerval = regs->xer;
 			if (ival < 0 && (ival & ((1ul << sh) - 1)) != 0)
-				regs->xer |= XER_CA;
+				op->xerval |= XER_CA;
 			else
-				regs->xer &= ~XER_CA;
+				op->xerval &= ~XER_CA;
 			goto logical_done;
 
 #ifdef __powerpc64__
 		case 27:	/* sld */
 			sh = regs->gpr[rb] & 0x7f;
 			if (sh < 64)
-				regs->gpr[ra] = regs->gpr[rd] << sh;
+				op->val = regs->gpr[rd] << sh;
 			else
-				regs->gpr[ra] = 0;
+				op->val = 0;
 			goto logical_done;
 
 		case 539:	/* srd */
 			sh = regs->gpr[rb] & 0x7f;
 			if (sh < 64)
-				regs->gpr[ra] = regs->gpr[rd] >> sh;
+				op->val = regs->gpr[rd] >> sh;
 			else
-				regs->gpr[ra] = 0;
+				op->val = 0;
 			goto logical_done;
 
 		case 794:	/* srad */
+			op->type = COMPUTE + SETREG + SETXER;
 			sh = regs->gpr[rb] & 0x7f;
 			ival = (signed long int) regs->gpr[rd];
-			regs->gpr[ra] = ival >> (sh < 64 ? sh : 63);
+			op->val = ival >> (sh < 64 ? sh : 63);
+			op->xerval = regs->xer;
 			if (ival < 0 && (sh >= 64 || (ival & ((1ul << sh) - 1)) != 0))
-				regs->xer |= XER_CA;
+				op->xerval |= XER_CA;
 			else
-				regs->xer &= ~XER_CA;
+				op->xerval &= ~XER_CA;
 			goto logical_done;
 
 		case 826:	/* sradi with sh_5 = 0 */
 		case 827:	/* sradi with sh_5 = 1 */
+			op->type = COMPUTE + SETREG + SETXER;
 			sh = rb | ((instr & 2) << 4);
 			ival = (signed long int) regs->gpr[rd];
-			regs->gpr[ra] = ival >> sh;
+			op->val = ival >> sh;
+			op->xerval = regs->xer;
 			if (ival < 0 && (ival & ((1ul << sh) - 1)) != 0)
-				regs->xer |= XER_CA;
+				op->xerval |= XER_CA;
 			else
-				regs->xer &= ~XER_CA;
+				op->xerval &= ~XER_CA;
 			goto logical_done;
 #endif /* __powerpc64__ */
 
@@ -1787,15 +1789,18 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 
  logical_done:
 	if (instr & 1)
-		set_cr0(regs, ra);
-	goto instr_done;
+		set_cr0(regs, op, ra);
+ logical_done_nocc:
+	op->reg = ra;
+	op->type |= SETREG;
+	return 1;
 
  arith_done:
 	if (instr & 1)
-		set_cr0(regs, rd);
-
- instr_done:
-	regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
+		set_cr0(regs, op, rd);
+ compute_done:
+	op->reg = rd;
+	op->type |= SETREG;
 	return 1;
 
  priv:
@@ -1886,6 +1891,92 @@ static nokprobe_inline void do_byterev(unsigned long *valp, int size)
 	}
 }
 
+/*
+ * Emulate an instruction that can be executed just by updating
+ * fields in *regs.
+ */
+void emulate_update_regs(struct pt_regs *regs, struct instruction_op *op)
+{
+	unsigned long next_pc;
+
+	next_pc = truncate_if_32bit(regs->msr, regs->nip + 4);
+	switch (op->type & INSTR_TYPE_MASK) {
+	case COMPUTE:
+		if (op->type & SETREG)
+			regs->gpr[op->reg] = op->val;
+		if (op->type & SETCC)
+			regs->ccr = op->ccval;
+		if (op->type & SETXER)
+			regs->xer = op->xerval;
+		break;
+
+	case BRANCH:
+		if (op->type & SETLK)
+			regs->link = next_pc;
+		if (op->type & BRTAKEN)
+			next_pc = op->val;
+		if (op->type & DECCTR)
+			--regs->ctr;
+		break;
+
+	case BARRIER:
+		switch (op->type & BARRIER_MASK) {
+		case BARRIER_SYNC:
+			mb();
+			break;
+		case BARRIER_ISYNC:
+			isync();
+			break;
+		case BARRIER_EIEIO:
+			eieio();
+			break;
+		case BARRIER_LWSYNC:
+			asm volatile("lwsync" : : : "memory");
+			break;
+		case BARRIER_PTESYNC:
+			asm volatile("ptesync" : : : "memory");
+			break;
+		}
+		break;
+
+	case MFSPR:
+		switch (op->spr) {
+		case SPRN_XER:
+			regs->gpr[op->reg] = regs->xer & 0xffffffffUL;
+			break;
+		case SPRN_LR:
+			regs->gpr[op->reg] = regs->link;
+			break;
+		case SPRN_CTR:
+			regs->gpr[op->reg] = regs->ctr;
+			break;
+		default:
+			WARN_ON_ONCE(1);
+		}
+		break;
+
+	case MTSPR:
+		switch (op->spr) {
+		case SPRN_XER:
+			regs->xer = op->val & 0xffffffffUL;
+			break;
+		case SPRN_LR:
+			regs->link = op->val;
+			break;
+		case SPRN_CTR:
+			regs->ctr = op->val;
+			break;
+		default:
+			WARN_ON_ONCE(1);
+		}
+		break;
+
+	default:
+		WARN_ON_ONCE(1);
+	}
+	regs->nip = next_pc;
+}
+
 /*
  * Emulate instructions that cause a transfer of control,
  * loads and stores, and a few other instructions.
@@ -1902,8 +1993,12 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 	int i, rd, nb;
 
 	r = analyse_instr(&op, regs, instr);
-	if (r != 0)
+	if (r < 0)
 		return r;
+	if (r > 0) {
+		emulate_update_regs(regs, &op);
+		return 1;
+	}
 
 	err = 0;
 	size = GETSIZE(op.type);