[PATCH bpf-next] perf/bpf: Use prog to emit ksymbol event for main program

Hou Tao
2024-07-14T06:55:17Z

From: Hou Tao <houtao1@huawei.com>

Since commit 0108a4e9f358 ("bpf: ensure main program has an extable"),
prog->aux->func[0]->kallsyms is left as uninitialized. For bpf program
with subprogs, the symbol for the main program is missed just as shown
in the output of perf script below:

ffffffff81284b69 qp_trie_lookup_elem+0xb9 ([kernel.kallsyms])
ffffffffc0011125 bpf_prog_a4a0eb0651e6af8b_lookup_qp_trie+0x5d (bpf...)
ffffffff8127bc2b bpf_for_each_array_elem+0x7b ([kernel.kallsyms])
ffffffffc00110a1 +0x25 ()
ffffffff8121a89a trace_call_bpf+0xca ([kernel.kallsyms])

Fix it by always using prog instead prog->aux->func[0] to emit ksymbol
event for the main program. After the fix, the output of perf script
will be correct:

ffffffff81284b96 qp_trie_lookup_elem+0xe6 ([kernel.kallsyms])
ffffffffc001382d bpf_prog_a4a0eb0651e6af8b_lookup_qp_trie+0x5d (bpf...)
ffffffff8127bc2b bpf_for_each_array_elem+0x7b ([kernel.kallsyms])
ffffffffc0013779 bpf_prog_245c55ab25cfcf40_qp_trie_lookup+0x25 (bpf...)
ffffffff8121a89a trace_call_bpf+0xca ([kernel.kallsyms])

Fixes: 0108a4e9f358 ("bpf: ensure main program has an extable")
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
Hi,

ksymbol for bpf program had been broken twice, and I think it is better
to add a bpf selftest for it, but I'm not so familiar with the
perf_event_open(), for now I just post the fix patch and will post the
selftest later.

kernel/events/core.c | 28 +++++++++++++---------------
1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f0128c5ff278..e1b7d9e61fa0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9289,21 +9289,19 @@ static void perf_event_bpf_emit_ksymbols(struct bpf_prog *prog,
bool unregister = type == PERF_BPF_EVENT_PROG_UNLOAD;
int i;

- if (prog->aux->func_cnt == 0) {
- perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF,
- (u64)(unsigned long)prog->bpf_func,
- prog->jited_len, unregister,
- prog->aux->ksym.name);
- } else {
- for (i = 0; i < prog->aux->func_cnt; i++) {
- struct bpf_prog *subprog = prog->aux->func[i];
-
- perf_event_ksymbol(
- PERF_RECORD_KSYMBOL_TYPE_BPF,
- (u64)(unsigned long)subprog->bpf_func,
- subprog->jited_len, unregister,
- subprog->aux->ksym.name);
- }
+ perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF,
+ (u64)(unsigned long)prog->bpf_func,
+ prog->jited_len, unregister,
+ prog->aux->ksym.name);
+
+ for (i = 1; i < prog->aux->func_cnt; i++) {
+ struct bpf_prog *subprog = prog->aux->func[i];
+
+ perf_event_ksymbol(
+ PERF_RECORD_KSYMBOL_TYPE_BPF,
+ (u64)(unsigned long)subprog->bpf_func,
+ subprog->jited_len, unregister,
+ subprog->aux->ksym.name);
}
}

--
2.29.2