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);
+