powerpc: Add emulation for the addpcis instruction

The addpcis instruction puts the sum of the next instruction address
plus a constant into a register.  Since the result depends on the
address of the instruction, it will give an incorrect result if it
is single-stepped out of line, which is what the *probes subsystem
will currently do if a probe is placed on an addpcis instruction.
This fixes the problem by adding emulation of it to analyse_instr().

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

arch/powerpc/lib/sstep.c

@@ -1021,9 +1021,6 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 			op->ccval = (regs->ccr & ~(1UL << (31 - rd))) |
 				(val << (31 - rd));
 			return 1;
-		default:
-			op->type = UNKNOWN;
-			return 0;
 		}
 		break;
 	case 31:
@@ -1123,6 +1120,17 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 		op->val = imm;
 		goto compute_done;
 
+	case 19:
+		if (((instr >> 1) & 0x1f) == 2) {
+			/* addpcis */
+			imm = (short) (instr & 0xffc1);	/* d0 + d2 fields */
+			imm |= (instr >> 15) & 0x3e;	/* d1 field */
+			op->val = regs->nip + (imm << 16) + 4;
+			goto compute_done;
+		}
+		op->type = UNKNOWN;
+		return 0;
+
 	case 20:	/* rlwimi */
 		mb = (instr >> 6) & 0x1f;
 		me = (instr >> 1) & 0x1f;