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

[Athira Rajeev]

> On 13 Jan 2025, at 8:59 PM, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> 
> On Mon, Jan 06, 2025 at 01:25:32PM -0800, Namhyung Kim wrote:
>> On Fri, Dec 27, 2024 at 04:18:32PM +0530, Athira Rajeev wrote:
>>> 
>>> 
>>>> On 23 Dec 2024, at 7:28 PM, Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx> wrote:
>>>> 
>>>> 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@xxxxxxxxxxxxxxxxxx>
>> 
>> Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> 
> Thanks, applied to perf-tools-next,
> 
> - Arnaldo

Thanks Namhyung and Arnaldo 

Athira.