powerpc/sstep: Add emulation support for ‘setb’ instruction

This adds emulation support for the following instruction:
   * Set Boolean (setb)
Signed-off-by: Sathvika Vasireddy <sathvika@linux.vnet.ibm.com>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7b735b0c898da0db2af8628a64df2f5114596f22.1620727160.git.sathvika@linux.vnet.ibm.com

arch/powerpc/lib/sstep.c

@@ -1700,6 +1700,28 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 			op->val = regs->ccr & imm;
 			goto compute_done;
 
+		case 128:	/* setb */
+			if (!cpu_has_feature(CPU_FTR_ARCH_300))
+				goto unknown_opcode;
+			/*
+			 * 'ra' encodes the CR field number (bfa) in the top 3 bits.
+			 * Since each CR field is 4 bits,
+			 * we can simply mask off the bottom two bits (bfa * 4)
+			 * to yield the first bit in the CR field.
+			 */
+			ra = ra & ~0x3;
+			/* 'val' stores bits of the CR field (bfa) */
+			val = regs->ccr >> (CR0_SHIFT - ra);
+			/* checks if the LT bit of CR field (bfa) is set */
+			if (val & 8)
+				op->val = -1;
+			/* checks if the GT bit of CR field (bfa) is set */
+			else if (val & 4)
+				op->val = 1;
+			else
+				op->val = 0;
+			goto compute_done;
+
 		case 144:	/* mtcrf */
 			op->type = COMPUTE + SETCC;
 			imm = 0xf0000000UL;