powerpc/sstep: Set NIP in instruction emulation tests

The tests for emulation of compute instructions execute and
emulate an instruction and then compare the results to verify the
emulation. In ISA v3.1 there are instructions that operate relative to
the NIP. Therefore set the NIP in the regs used for the emulated
instruction to the location of the executed instruction so they will
give the same result.

This is a rework of a patch by Balamuruhan S.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200525025923.19843-3-jniethe5@gmail.com

arch/powerpc/lib/test_emulate_step.c

@@ -1011,11 +1011,14 @@ static struct compute_test compute_tests[] = {
 static int __init emulate_compute_instr(struct pt_regs *regs,
 					struct ppc_inst instr)
 {
+	extern s32 patch__exec_instr;
 	struct instruction_op op;
 
 	if (!regs || !ppc_inst_val(instr))
 		return -EINVAL;
 
+	regs->nip = patch_site_addr(&patch__exec_instr);
+
 	if (analyse_instr(&op, regs, instr) != 1 ||
 	    GETTYPE(op.type) != COMPUTE) {
 		pr_info("emulation failed, instruction = 0x%08x\n", ppc_inst_val(instr));