[PATCH V8 01/10] powerpc, perf: Drop the branch sample when 'from' cannot be fetched

[Anshuman Khandual]

BHRB is a rolling buffer. Hence we might end up in a situation where
we have read one target address but when we try to read the next entry
indicating the from address of the targe, the buffer just overflows.
In this case, the captured from address will be zero which indicates
the end of the buffer.

This patch drops the entire branch record which would have otherwise
confused the user space tools.

Signed-off-by: Anshuman Khandual <khandual at linux.vnet.ibm.com>
---
 arch/powerpc/perf/core-book3s.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 12b6384..c246e65 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -452,7 +452,6 @@ static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
 			 *    In this case we need to read the instruction from
 			 *    memory to determine the target/to address.
 			 */
-
 			if (val & BHRB_TARGET) {
 				/* Target branches use two entries
 				 * (ie. computed gotos/XL form)
@@ -463,6 +462,8 @@ static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
 
 				/* Get from address in next entry */
 				val = read_bhrb(r_index++);
+				if (!val)
+					break;
 				addr = val & BHRB_EA;
 				if (val & BHRB_TARGET) {
 					/* Shouldn't have two targets in a
-- 
2.1.0