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

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Message-ID: <Z4UxQSAKoLskEILD@x1>
Date: Mon, 13 Jan 2025 12:29:05 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, jolsa@...nel.org,
	adrian.hunter@...el.com, irogers@...gle.com, hbathini@...ux.ibm.com,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, maddy@...ux.ibm.com,
	kjain@...ux.ibm.com, disgoel@...ux.vnet.ibm.com
Subject: Re: [PATCH] tools/perf: Fix segfault during perf record --off-cpu
 when debuginfo is not enabled

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@...ux.vnet.ibm.com> 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@...ux.vnet.ibm.com>
> 
> Reviewed-by: Namhyung Kim <namhyung@...nel.org>

Thanks, applied to perf-tools-next,

- Arnaldo