On 7/14/25 4:49 PM, Ihor Solodrai wrote:
On 7/8/25 1:07 PM, Alexei Starovoitov wrote:
On Thu, Jul 3, 2025 at 5:18 AM Menglong Dong
<menglong8.dong@xxxxxxxxx> wrote:
+ return true;
+
+ /* Following symbols have multi definition in kallsyms, take
+ * "t_next" for example:
+ *
+ * ffffffff813c10d0 t t_next
+ * ffffffff813d31b0 t t_next
+ * ffffffff813e06b0 t t_next
+ * ffffffff813eb360 t t_next
+ * ffffffff81613360 t t_next
+ *
+ * but only one of them have corresponding mrecord:
+ * ffffffff81613364 t_next
+ *
+ * The kernel search the target function address by the symbol
+ * name "t_next" with kallsyms_lookup_name() during attaching
+ * and the function "0xffffffff813c10d0" can be matched, which
+ * doesn't have a corresponding mrecord. And this will make
+ * the attach failing. Skip the functions like this.
+ *
+ * The list maybe not whole, so we still can fail......We need a
+ * way to make the whole things right. Yes, we need fix it :/
+ */
+ if (!strcmp(name, "kill_pid_usb_asyncio"))
+ return true;
+ if (!strcmp(name, "t_next"))
+ return true;
+ if (!strcmp(name, "t_stop"))
+ return true;
This little patch will filter out from BTF any static functions with
the same name that appear more than once.
diff --git a/btf_encoder.c b/btf_encoder.c
index 0bc2334..6441269 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -96,7 +96,8 @@ struct elf_function {
const char *name;
char *alias;
size_t prefixlen;
- bool kfunc;
+ uint8_t is_static:1;
+ uint8_t kfunc:1;
uint32_t kfunc_flags;
};
@@ -1374,7 +1375,7 @@ static int saved_functions_combine(struct
btf_encoder_func_state *a, struct btf_
return ret;
optimized = a->optimized_parms | b->optimized_parms;
unexpected = a->unexpected_reg | b->unexpected_reg;
- inconsistent = a->inconsistent_proto | b->inconsistent_proto;
+ inconsistent = a->inconsistent_proto | b->inconsistent_proto |
a->elf->is_static | b->elf->is_static;
if (!unexpected && !inconsistent && !funcs__match(a, b))
inconsistent = 1;
a->optimized_parms = b->optimized_parms = optimized;
@@ -1461,6 +1462,8 @@ static void elf_functions__collect_function(struct
elf_functions *functions, GEl
func = &functions->entries[functions->cnt];
func->name = name;
+ func->is_static = elf_sym__bind(sym) == STB_LOCAL;
+
if (strchr(name, '.')) {
const char *suffix = strchr(name, '.');
See the full BTF functions diff here (from vmlinux 6.15.3):
https://gist.github.com/theihor/3f8fabc32d916e592f8e84f434d9950c
This covers t_next and t_stop, but not all functions in the list. Some
of them are not static, such as kill_pid_usb_asyncio [1]. And p_next,
for example, appears only once [2].
So filtering statics in pahole might not be the only problem here.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/signal.c#n1521
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/trace/trace_events.c#n1717
This looks like pahole bug. It shouldn't emit BTF for static
functions with the same name in different files.
I recall we discussed it in the past and I thought the fix had landed.
I checked this particular case (the t_next function), and what seems
to be happening is that all function prototypes match, according to
this check in pahole's BTF encoding:
* https://github.com/acmel/dwarves/blob/v1.30/btf_encoder.c#L1378
* https://github.com/acmel/dwarves/blob/v1.30/btf_encoder.c#L1112-L1152
That is: the name, number and types of parameters all match.
So at least according to the current pahole logic the prototypes are
*consistent*. As a result, a single BTF function t_next is emitted.
Maybe funcs__match() check should be even more strict? Say, disallow
static functions?
I am not sure that the draft that Jiri sent [1] is right as it just
filters out duplicates by name.
[1] https://lore.kernel.org/bpf/aHD0IdJBqd3XNybw@krava/
