selftests/powerpc/pmu: Add support for branch sampling in get_intr_regs function

Add support for sample type as PERF_SAMPLE_BRANCH_STACK in sampling
tests. This change is a precursor/helper for sampling testcases, that
test branck stack feature in perf interface.
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220610134113.62991-5-atrajeev@linux.vnet.ibm.com

tools/testing/selftests/powerpc/pmu/sampling_tests/misc.c

@@ -259,13 +259,32 @@ u64 *get_intr_regs(struct event *event, void *sample_buff)
 	u64 *intr_regs;
 	size_t size = 0;
 
-	if ((type ^ PERF_SAMPLE_REGS_INTR))
+	if ((type ^ (PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_BRANCH_STACK)) &&
+			(type  ^ PERF_SAMPLE_REGS_INTR))
 		return NULL;
 
 	intr_regs = (u64 *)perf_read_first_sample(sample_buff, &size);
 	if (!intr_regs)
 		return NULL;
 
+	if (type & PERF_SAMPLE_BRANCH_STACK) {
+		/*
+		 * PERF_RECORD_SAMPLE and PERF_SAMPLE_BRANCH_STACK:
+		 * struct {
+		 *     struct perf_event_header hdr;
+		 *     u64 number_of_branches;
+		 *     struct perf_branch_entry[number_of_branches];
+		 *     u64 data[];
+		 * };
+		 * struct perf_branch_entry {
+		 *     u64	from;
+		 *     u64	to;
+		 *     u64	misc;
+		 * };
+		 */
+		intr_regs += ((*intr_regs) * 3) + 1;
+	}
+
 	/*
 	 * First entry in the sample buffer used to specify
 	 * PERF_SAMPLE_REGS_ABI_64, skip perf regs abi to access