From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48A78C3DA6F for ; Thu, 24 Aug 2023 16:10:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242388AbjHXQKN (ORCPT ); Thu, 24 Aug 2023 12:10:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242427AbjHXQKF (ORCPT ); Thu, 24 Aug 2023 12:10:05 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 35FD41995; Thu, 24 Aug 2023 09:10:03 -0700 (PDT) Received: from pwmachine.localnet (85-170-34-233.rev.numericable.fr [85.170.34.233]) by linux.microsoft.com (Postfix) with ESMTPSA id D3FD92127C69; Thu, 24 Aug 2023 09:10:01 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com D3FD92127C69 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1692893402; bh=Olop74Ds2RRFnMuhvLh1fh38MEe0raHrxEM8ELUBzcs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bZ8CUZ67oSQkysa52iR2no0FMbicRah2q+hauCQibUuhABkuiHNWZIDjVfpQ2Hd1a Qhhcwj64S5nFdOdVr22XsqfA3J7cdB0sq1sWL0sL1DST8UIsI/jFodgYk8eDuW6X7N h5SSVMUyAzeMEQhPmeDhmKea4sWHEy6qPk+XDcvQ= From: Francis Laniel To: Masami Hiramatsu Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Steven Rostedt Subject: Re: [RFC PATCH v2 1/1] tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols Date: Thu, 24 Aug 2023 18:09:59 +0200 Message-ID: <13333844.uLZWGnKmhe@pwmachine> In-Reply-To: <20230824234721.1b481cd5d0b8bbc43a24d9a6@kernel.org> References: <20230824103734.53453-1-flaniel@linux.microsoft.com> <12271275.O9o76ZdvQC@pwmachine> <20230824234721.1b481cd5d0b8bbc43a24d9a6@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Le jeudi 24 ao=FBt 2023, 16:47:21 CEST Masami Hiramatsu a =E9crit : > On Thu, 24 Aug 2023 16:31:13 +0200 >=20 > Francis Laniel wrote: > > Hi. > >=20 > > Le jeudi 24 ao=FBt 2023, 15:02:27 CEST Masami Hiramatsu a =E9crit : > > > On Thu, 24 Aug 2023 12:37:34 +0200 > > >=20 > > > Francis Laniel wrote: > > > > Previously to this commit, if func matches several symbols, a kprob= e, > > > > being > > > > either sysfs or PMU, would only be installed for the first matching > > > > address. This could lead to some misunderstanding when some BPF code > > > > was > > > > never called because it was attached to a function which was indeed > > > > not > > > > call, because the effectively called one has no kprobes. > > > >=20 > > > > So, this commit returns EADDRNOTAVAIL when func matches several > > > > symbols. > > > > This way, user needs to use addr to remove the ambiguity. > > >=20 > > > Thanks for update the patch. I have some comments there. > > >=20 > > > > Suggested-by: Masami Hiramatsu > > > > Signed-off-by: Francis Laniel > > > > Link: > > > > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea74= 2@k > > > > ern > > > > el.org/ --- > > > >=20 > > > > kernel/trace/trace_kprobe.c | 42 > > > > +++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 42 insertions(+) > > > >=20 > > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprob= e.c > > > > index 23dba01831f7..0c8dd6ba650b 100644 > > > > --- a/kernel/trace/trace_kprobe.c > > > > +++ b/kernel/trace/trace_kprobe.c > > > > @@ -705,6 +705,25 @@ static struct notifier_block > > > > trace_kprobe_module_nb =3D > > > > {> > > > >=20 > > > > .priority =3D 1 /* Invoked after kprobe module callback */ > > > > =20 > > > > }; > > > >=20 > > > > +static int count_symbols(void *data, unsigned long unused) > > > > +{ > > > > + unsigned int *count =3D data; > > > > + > > > > + (*count)++; > > > > + > > > > + return 0; > > > > +} > > > > + > > > > +static unsigned int func_name_several_symbols(char *func_name) > > >=20 > > > If this returns boolean, please use 'bool' for return type. > > > Also, I think 'func_name_is_unique()' is more natural. > >=20 > > This name sounds better but it means it will check count =3D=3D 1. > > I am fine with it, but please see my below comment. > >=20 > > > > +{ > > > > + unsigned int count; > > > > + > > > > + count =3D 0; > > > > + kallsyms_on_each_match_symbol(count_symbols, func_name, &count); > > > > + > > > > + return count > 1; > > > > +} > > > > + > > > >=20 > > > > static int __trace_kprobe_create(int argc, const char *argv[]) > > > > { > > > > =20 > > > > /* > > > >=20 > > > > @@ -836,6 +855,18 @@ static int __trace_kprobe_create(int argc, con= st > > > > char > > > > *argv[])> > > > >=20 > > > > } > > > > =09 > > > > } > > > >=20 > > > > + /* > > > > + * If user specifies KSYM, we check it does not correspond to > > > > several > > > > + * symbols. > > > > + * If this is the case, we return EADDRNOTAVAIL to indicate the u= ser > > > > + * he/she should use ADDR rather than KSYM to remove the ambiguit= y. > > > > + */ > > > > + if (symbol && func_name_several_symbols(symbol)) { > > >=20 > > > Then, here will be > > >=20 > > > if (symbol && !func_name_is_unique(symbol)) { > >=20 > > I am fine with the above, but it means if users gives an unknown symbol, > > we > > will return EADDRNOTAVAIL instead of currently returning ENOENT. > > Is it OK? >=20 > Ah, good catch! Hm, then what about 'int number_of_same_symbols()' ? >=20 >=20 > if (symbol) { > num =3D number_of_same_symbols(symbol); > if (num > 1) > return -EADDRNOTAVAIL; > else if (num =3D=3D 0) > return -ENOENT; > } Done in the v3 :D! > Thank you, >=20 > > > > + ret =3D -EADDRNOTAVAIL; > > > > + > > > > + goto error; > > > > + } > > > > + > > > >=20 > > > > trace_probe_log_set_index(0); > > > > if (event) { > > > > =09 > > > > ret =3D traceprobe_parse_event_name(&event, &group, gbuf, > > > >=20 > > > > @@ -1699,6 +1730,7 @@ static int unregister_kprobe_event(struct > > > > trace_kprobe *tk)> > > > >=20 > > > > } > > > > =20 > > > > #ifdef CONFIG_PERF_EVENTS > > > >=20 > > > > + > > > >=20 > > > > /* create a trace_kprobe, but don't add it to global lists */ > > > > struct trace_event_call * > > > > create_local_trace_kprobe(char *func, void *addr, unsigned long of= fs, > > > >=20 > > > > @@ -1709,6 +1741,16 @@ create_local_trace_kprobe(char *func, void > > > > *addr, > > > > unsigned long offs,> > > > >=20 > > > > int ret; > > > > char *event; > > > >=20 > > > > + /* > > > > + * If user specifies func, we check that function name does not > > > > + * correspond to several symbols. > > > > + * If this is the case, we return EADDRNOTAVAIL to indicate the u= ser > > > > + * he/she should use addr and offs rather than func to remove the > > > > + * ambiguity. > > > > + */ > > > > + if (func && func_name_several_symbols(func)) > > >=20 > > > Ditto. > > >=20 > > > Thanks! > > >=20 > > > > + return ERR_PTR(-EADDRNOTAVAIL); > > > > + > > > >=20 > > > > /* > > > > =09 > > > > * local trace_kprobes are not added to dyn_event, so they are ne= ver > > > > * searched in find_trace_kprobe(). Therefore, there is no concern > > > > of > >=20 > > Best regards.