[PATCH] tools/perf: Fix segfault during perf record --off-cpu when debuginfo is not enabled

Athira Rajeev
2024-12-23T13:58:35Z

When kernel is built without debuginfo, running perf record with
--off-cpu results in segfault as below:

./perf record --off-cpu -e dummy sleep 1
libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
libbpf: failed to find '.BTF' ELF section in /lib/modules/6.13.0-rc3+/build/vmlinux
libbpf: failed to find valid kernel BTF
Segmentation fault (core dumped)

The backtrace pointed to:

#0 0x00000000100fb17c in btf.type_cnt ()
#1 0x00000000100fc1a8 in btf_find_by_name_kind ()
#2 0x00000000100fc38c in btf.find_by_name_kind ()
#3 0x00000000102ee3ac in off_cpu_prepare ()
#4 0x000000001002f78c in cmd_record ()
#5 0x00000000100aee78 in run_builtin ()
#6 0x00000000100af3e4 in handle_internal_command ()
#7 0x000000001001004c in main ()

Code sequence is:
static void check_sched_switch_args(void)
{
struct btf *btf = btf__load_vmlinux_btf();
const struct btf_type *t1, *t2, *t3;
u32 type_id;

type_id = btf__find_by_name_kind(btf, "btf_trace_sched_switch",
BTF_KIND_TYPEDEF);

btf__load_vmlinux_btf fails when CONFIG_DEBUG_INFO_BTF is not enabled.
Here bpf__find_by_name_kind calls btf__type_cnt with NULL btf
value and results in segfault. To fix this, add a check to see if
btf is not NULL before invoking bpf__find_by_name_kind

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
tools/perf/util/bpf_off_cpu.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index a590a8ac1f9d..4269b41d1771 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -100,6 +100,11 @@ static void check_sched_switch_args(void)
const struct btf_type *t1, *t2, *t3;
u32 type_id;

+ if (!btf) {
+ pr_debug("Missing btf, check if CONFIG_DEBUG_INFO_BTF is enabled\n");
+ goto cleanup;
+ }
+
type_id = btf__find_by_name_kind(btf, "btf_trace_sched_switch",
BTF_KIND_TYPEDEF);
if ((s32)type_id < 0)
--
2.43.5