[PATCH 1/5] powerpc/perf: Drop the branch sample when 'from' cannot be fetched

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

BHRB (Branch History Rolling Buffer) 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 target address, 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@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 d90893b..b0c2d53 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -461,7 +461,6 @@ 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)
@@ -472,6 +471,8 @@ 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