[PATCH 1/2] perf probe: Prevent segfault when reading probe point with absolute address

[Wang Nan <wangnan0@huawei.com>]

'perf probe -l' panic if there is a manually inserted probing point
with absolute address. For example:

 # echo 'p:probe/abs_ffffffff811e6615 0xffffffff811e6615' > /sys/kernel/debug/tracing/kprobe_events
 # perf probe -l
 Segmentation fault (core dumped)

This patch fix this problem by considering the situation that
"tp->symbol == NULL" in find_perf_probe_point_from_dwarf() and
find_perf_probe_point_from_map().

After this patch:

 # perf probe -l
 probe:abs_ffffffff811e6615 (on SyS_write+5@fs/read_write.c)

And when debug info is missing:

 # rm -rf ~/.debug
 # mv /lib/modules/4.2.0-rc1+/build/vmlinux /lib/modules/4.2.0-rc1+/build/vmlinux.bak
 # perf probe -l
 probe:abs_ffffffff811e6615 (on sys_write+5)

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/probe-event.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index f07374b..6c7e538 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -515,7 +515,7 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
 		if (ret < 0)
 			goto error;
 		addr += stext;
-	} else {
+	} else if (tp->symbol) {
 		addr = kernel_get_symbol_address_by_name(tp->symbol, false);
 		if (addr == 0)
 			goto error;
@@ -1815,17 +1815,17 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
 {
 	struct symbol *sym = NULL;
 	struct map *map;
-	u64 addr;
+	u64 addr = tp->address;
 	int ret = -ENOENT;
 
 	if (!is_kprobe) {
 		map = dso__new_map(tp->module);
 		if (!map)
 			goto out;
-		addr = tp->address;
 		sym = map__find_symbol(map, addr, NULL);
 	} else {
-		addr = kernel_get_symbol_address_by_name(tp->symbol, true);
+		if (tp->symbol)
+			addr = kernel_get_symbol_address_by_name(tp->symbol, true);
 		if (addr) {
 			addr += tp->offset;
 			sym = __find_kernel_function(addr, &map);
-- 
1.8.3.4