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 CAE72C71153 for ; Thu, 24 Aug 2023 14:32:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237561AbjHXObd (ORCPT ); Thu, 24 Aug 2023 10:31:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236573AbjHXObT (ORCPT ); Thu, 24 Aug 2023 10:31:19 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 874D2193; Thu, 24 Aug 2023 07:31:17 -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 01DFF2127C82; Thu, 24 Aug 2023 07:31:15 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 01DFF2127C82 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1692887477; bh=61ICIakGF6sK32UmdQ+e62JH2BHe9zBGVoTWqkCNx3k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=B+MKGEeTjDNJVpbzDr7sNF82lF/Re2GA2IV4jQi7enKyDbV2QovfSKEUUHxyWpMKO vqh8agHw7Iga0jWu5wblyjWCR4FG+4qzdQaBesr4fy3JxritHMPV04FAgw92IvV47w IL3NnuACLxYFIGHQ89PpQc5X1VXGD41xUKSVG0co= From: Francis Laniel To: Masami Hiramatsu Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , 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 16:31:13 +0200 Message-ID: <12271275.O9o76ZdvQC@pwmachine> In-Reply-To: <20230824220227.01c367c1d7b6219a79cf2843@kernel.org> References: <20230824103734.53453-1-flaniel@linux.microsoft.com> <20230824103734.53453-2-flaniel@linux.microsoft.com> <20230824220227.01c367c1d7b6219a79cf2843@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-kernel@vger.kernel.org Hi. 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 kprobe, > > 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.b0c104ae4494a7d1f2eea742@ke= rn > > 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_kprobe.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_n= b =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. > > +{ > > + 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, const c= har > > *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 user > > + * he/she should use ADDR rather than KSYM to remove the ambiguity. > > + */ > > + 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= =20 will return EADDRNOTAVAIL instead of currently returning ENOENT. Is it OK? > > + 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 offs, > >=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 user > > + * 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 never > > * searched in find_trace_kprobe(). Therefore, there is no concern of Best regards.