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From:   Jin Yao <yao.jin@linux.intel.com>
To:     acme@kernel.org, jolsa@kernel.org, peterz@infradead.org,
        mingo@redhat.com, alexander.shishkin@linux.intel.com
Cc:     Linux-kernel@vger.kernel.org, ak@linux.intel.com,
        kan.liang@intel.com, yao.jin@intel.com,
        Jin Yao <yao.jin@linux.intel.com>
Subject: [PATCH] perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set
Date:   Wed,  5 Aug 2020 10:29:37 +0800
Message-Id: <20200805022937.29184-1-yao.jin@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

We received an error report that perf-record caused 'Segmentation fault'
on a newly system (e.g. on the new installed ubuntu).

 (gdb) backtrace
 #0  __read_once_size (size=4, res=<synthetic pointer>, p=0x14) at /root/0-jinyao/acme/tools/include/linux/compiler.h:139
 #1  atomic_read (v=0x14) at /root/0-jinyao/acme/tools/include/asm/../../arch/x86/include/asm/atomic.h:28
 #2  refcount_read (r=0x14) at /root/0-jinyao/acme/tools/include/linux/refcount.h:65
 #3  perf_mmap__read_init (map=map@entry=0x0) at mmap.c:177
 #4  0x0000561ce5c0de39 in perf_evlist__poll_thread (arg=0x561ce68584d0) at util/sideband_evlist.c:62
 #5  0x00007fad78491609 in start_thread (arg=<optimized out>) at pthread_create.c:477
 #6  0x00007fad7823c103 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

The root cause is, evlist__add_bpf_sb_event() just returns 0 if
HAVE_LIBBPF_SUPPORT is not defined (inline function path). So it will
not create a valid evsel for side-band event.

But perf-record still creates BPF side band thread to process the
side-band event, then the error happpens.

We can reproduce this issue by removing the libelf-dev. e.g.
1. apt-get remove libelf-dev
2. perf record -a -- sleep 1

root@test:~# ./perf record -a -- sleep 1
perf: Segmentation fault
Obtained 6 stack frames.
./perf(+0x28eee8) [0x5562d6ef6ee8]
/lib/x86_64-linux-gnu/libc.so.6(+0x46210) [0x7fbfdc65f210]
./perf(+0x342e74) [0x5562d6faae74]
./perf(+0x257e39) [0x5562d6ebfe39]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x9609) [0x7fbfdc990609]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x43) [0x7fbfdc73b103]
Segmentation fault (core dumped)

To fix this issue,

1. We either install the missing libraries to let HAVE_LIBBPF_SUPPORT
   be defined.
   e.g. apt-get install libelf-dev and install other related libraries.

2. Use this patch to skip the side-band event setup if HAVE_LIBBPF_SUPPORT
   is not set.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
---
 tools/perf/builtin-record.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index b6bdccd875bc..ae97f98e2753 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1506,6 +1506,7 @@ static int record__synthesize(struct record *rec, bool tail)
 	return err;
 }
 
+#ifdef HAVE_LIBBPF_SUPPORT
 static int record__process_signal_event(union perf_event *event __maybe_unused, void *data)
 {
 	struct record *rec = data;
@@ -1550,6 +1551,12 @@ static int record__setup_sb_evlist(struct record *rec)
 
 	return 0;
 }
+#else
+static int record__setup_sb_evlist(struct record *rec __maybe_unused)
+{
+	return 0;
+}
+#endif
 
 static int __cmd_record(struct record *rec, int argc, const char **argv)
 {
-- 
2.17.1