bpf, events: Use prog to emit ksymbol event for main program

Since commit 0108a4e9f358 ("bpf: ensure main program has an extable"),
prog->aux->func[0]->kallsyms is left as uninitialized. For BPF programs
with subprogs, the symbol for the main program is missing 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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Yonghong Song <yonghong.song@linux.dev>
Reviewed-by: Krister Johansen <kjlx@templeofstupid.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20240714065533.1112616-1-houtao@huaweicloud.com

diff --git a/kernel/events/core.c b/kernel/events/core.c
index ab6c4c942f7965fa08cf15018aabe6e57d9e4a71..eeb585404e1188a04896ff974969aa3091efc29a 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9327,21 +9327,19 @@ 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);
        }
 }