[PATCH v2 2/3] perf tools powerpc: Fix crash if callchain is empty

[Sandipan Das <sandipan@linux.vnet.ibm.com>]

For some cases, the callchain provided by the kernel may be
empty. So, the callchain ip filtering code will cause a crash
if we do not check whether the struct ip_callchain pointer is
NULL before accessing any members.

This can be observed on a powerpc64le system running Fedora 27
as shown below.

 # perf record -b -e cycles:u ls
 # perf report --branch-history
 perf: Segmentation fault
 -------- backtrace --------
 perf[0x1027615c]
 linux-vdso64.so.1(__kernel_sigtramp_rt64+0x0)[0x7fff856304d8]
 perf(arch_skip_callchain_idx+0x44)[0x10257c58]
 perf[0x1017f2e4]
 perf(thread__resolve_callchain+0x124)[0x1017ff5c]
 perf(sample__resolve_callchain+0xf0)[0x10172788]
 ...

Reported-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
---
 tools/perf/arch/powerpc/util/skip-callchain-idx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index d3a13f79d3ee..910db8762120 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -262,7 +262,7 @@ int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
 	int rc;
 	u64 skip_slot = -1;
 
-	if (chain->nr < 3)
+	if (!chain || chain->nr < 3)
 		return skip_slot;
 
 	rc = check_return_addr(thread, chain->ips[1]);
-- 
2.14.3