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From: Ihor Solodrai To: Alexei Starovoitov , Menglong Dong , Alan Maguire , Jiri Olsa Cc: bpf , Eduard Zingerman , Andrii Nakryiko , Arnaldo Carvalho de Melo , dwarves@vger.kernel.org References: <20250703121521.1874196-1-dongml2@chinatelecom.cn> <20250703121521.1874196-18-dongml2@chinatelecom.cn> <9771eaa3-413a-4ab0-b7e1-d6a6f326c43f@linux.dev> Content-Language: en-US In-Reply-To: <9771eaa3-413a-4ab0-b7e1-d6a6f326c43f@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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 >> 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/ >