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 1264AC7EE2C for ; Fri, 25 Aug 2023 14:16:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231249AbjHYOQP (ORCPT ); Fri, 25 Aug 2023 10:16:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343784AbjHYOQL (ORCPT ); Fri, 25 Aug 2023 10:16:11 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DB2F5E7B; Fri, 25 Aug 2023 07:15:46 -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 674A12127C8E; Fri, 25 Aug 2023 07:14:28 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 674A12127C8E DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1692972869; bh=IvnlCxT9OzH+XyEs7D1JGVlaY/IFvzfIeDzzNfzltlg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bXAyBKt8FeloYhXE+bte2WarGugFyn4nFWjVfP/BFtT8yaqoENwU18zQF1SWvcvrV LU5+T24W47wvzxUbxWMVOMaAwm2sj2Yj/L1kgin9S04Vbanz5qlMR4Z56lcCQXuaLw b9y9yXA2bxvKJ0B5uo0thwAuWtEd0Om5SF7pBBAk= From: Francis Laniel To: Masami Hiramatsu Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH v3 1/1] tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols Date: Fri, 25 Aug 2023 16:14:25 +0200 Message-ID: <1862303.tdWV9SEqCh@pwmachine> In-Reply-To: <20230825221321.faaa33e03afc48abc345c24f@kernel.org> References: <20230824160859.66113-1-flaniel@linux.microsoft.com> <5704161.DvuYhMxLoT@pwmachine> <20230825221321.faaa33e03afc48abc345c24f@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 vendredi 25 ao=FBt 2023, 15:13:21 CEST Masami Hiramatsu a =E9crit : > On Fri, 25 Aug 2023 14:34:49 +0200 >=20 > Francis Laniel wrote: > > Hi. > >=20 > > Le vendredi 25 ao=FBt 2023, 14:16:49 CEST Masami Hiramatsu a =E9crit : > > > On Thu, 24 Aug 2023 18:08:59 +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 > > > > called, because the effectively called one has no kprobes attached. > > > >=20 > > > > So, this commit returns EADDRNOTAVAIL when func matches several > > > > symbols. > > > > This way, user needs to use address to remove the ambiguity. > > > >=20 > > > > Suggested-by: Masami Hiramatsu > > > > Signed-off-by: Francis Laniel > > > > Link: > > > > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea74= 2@k > > > > ern > > > > el.org/ --- > > >=20 > > > Ah, this should be fine, but selftest (tools/testing/selftests/ftrace) > > > fails. > > >=20 > > > # tail 60-kprobe_module.tc-log.vsOHnF > > >=20 > > > ... > > > + : > > > + : 'Add an event on a module function without specifying event name' > > > + : > > > + echo 'p trace_printk:trace_printk_irq_work' > > > sh: write error: No such file or directory > > >=20 > > > Ah, the function on non-exist module should be checked too. > > >=20 > > > # tail 63-kprobe_syntax_errors.tc-log.mMLwIQ > > > + + printfwc '%s' -c > > >=20 > > > 'p ' > > >=20 > > > + pos=3D2 > > > + printf+ '%s'tr 'p ^non_exist_func' > > >=20 > > > -d ^ > > >=20 > > > + command=3D'p non_exist_func' > > > + echo 'Test command: p non_exist_func' > > > Test command: p non_exist_func > > > + echo > > > + grep 'trace_kprobe: error:' -A 3 error_log > > >=20 > > > Also, this doesn't leave a syntax error message. > > >=20 > > > So, the below changes are needed. > >=20 > > Excellent catch! Thank you, I will apply this patch and send v4 right > > after. Regarding test, do you think I can add a test for the > > EADDRNOTAVAIL case? > Hmm, in that case, you need to change something in tracefs/README so that > we can identify the kernel has different behavior. Or we have to change > this is a "Fix" for backporting. Oops, sorry I sent the v4 with a test but as a separated commit, so we can= =20 just ignore it for the moment. > > Maybe it should go inside LTP? As this would need having a kernel compi= led > > with a name pointing to several symbols? >=20 > For this tracing feature, I rather like to use > tools/testing/selftests/ftrace to test it. And it is used on all stable > kernel, that is why we need to add some change on tracefs/README or > something. >=20 > But I would like to wait for Alessandro's work. After his work, in this t= ime > we need to probe all the same-name symbols as your original patch does. > This is because 1:n mapping can happen as Alessandro pointed in >=20 > https://lore.kernel.org/all/CAPp5cGQsRdB0+KHR1wX2bDDdc5sTzSNPA417PNJb0ypm= V=3Dy > S6w@mail.gmail.com/ >=20 > But if his feature is configurable (and maybe so), we need to keep this > version... We have many options. >=20 > - this normal kallsyms: the same-name symbols should not be used. > - enhanced kallsyms (if 1:n symbol has the same suffix): the same name > symbols should be probed at once. > - enhanced kallsyms (if 1:n symbol has different suffix): the same-name > symbol must not exist. I understand! In future case, we could still have a test and change its behavior (i.e.=20 potentially skipping it) when KALLSYMS_ALIAS is set. > > Also, should some man pages somewhere be updated to reflect the case > > kprobe can return EADDRNOTAVAIL? >=20 > No, it is a tracefs interface and we don't have man pages yet. I was more thinking to the PMU counterpart as it is created through=20 perf_event_open()? > Thank you, >=20 > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > > > index 8ab46a2a446d..1e57bc896952 100644 > > > --- a/kernel/trace/trace_kprobe.c > > > +++ b/kernel/trace/trace_kprobe.c > > > @@ -855,7 +855,7 @@ static int __trace_kprobe_create(int argc, const > > > char > > > *argv[]) } > > >=20 > > > } > > >=20 > > > - if (symbol) { > > > + if (symbol && !strchr(symbol, ':')) { > > >=20 > > > unsigned int count; > > > =09 > > > count =3D number_of_same_symbols(symbol); > > >=20 > > > @@ -864,6 +864,7 @@ static int __trace_kprobe_create(int argc, const > > > char > > > *argv[]) * Users should use ADDR to remove the ambiguity of > > >=20 > > > * using KSYM only. > > > */ > > >=20 > > > + trace_probe_log_err(0, NON_UNIQ_SYMBOL); > > >=20 > > > ret =3D -EADDRNOTAVAIL; > > > =09 > > > goto error; > > >=20 > > > @@ -872,6 +873,7 @@ static int __trace_kprobe_create(int argc, const > > > char > > > *argv[]) * We can return ENOENT earlier than when register the > > >=20 > > > * kprobe. > > > */ > > >=20 > > > + trace_probe_log_err(0, BAD_PROBE_ADDR); > > >=20 > > > ret =3D -ENOENT; > > > =09 > > > goto error; > > >=20 > > > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h > > > index 7f929482e8d4..a4f478448eef 100644 > > > --- a/kernel/trace/trace_probe.h > > > +++ b/kernel/trace/trace_probe.h > > > @@ -450,6 +450,7 @@ extern int traceprobe_define_arg_fields(struct > > > trace_event_call *event_call, C(BAD_MAXACT, "Invalid maxactive > > > number"), \ > > >=20 > > > C(MAXACT_TOO_BIG, "Maxactive is too big"), \ > > > C(BAD_PROBE_ADDR, "Invalid probed address or symbol"), \ > > >=20 > > > + C(NON_UNIQ_SYMBOL, "The symbol is not unique"), \ > > >=20 > > > C(BAD_RETPROBE, "Retprobe address must be an function > >=20 > > entry"), \ > >=20 > > > C(NO_TRACEPOINT, "Tracepoint is not found"), \ > > > C(BAD_ADDR_SUFFIX, "Invalid probed address suffix"), \ > > >=20 > > > Thank you, > > >=20 > > > > kernel/trace/trace_kprobe.c | 61 > > > > +++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 61 insertions(+) > > > >=20 > > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprob= e.c > > > > index 23dba01831f7..2f393739e8cf 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 number_of_same_symbols(char *func_name) > > > > +{ > > > > + unsigned int count; > > > > + > > > > + count =3D 0; > > > > + kallsyms_on_each_match_symbol(count_symbols, func_name, &count); > > > > + > > > > + return count; > > > > +} > > > > + > > > >=20 > > > > static int __trace_kprobe_create(int argc, const char *argv[]) > > > > { > > > > =20 > > > > /* > > > >=20 > > > > @@ -836,6 +855,29 @@ static int __trace_kprobe_create(int argc, con= st > > > > char > > > > *argv[])> > > > >=20 > > > > } > > > > =09 > > > > } > > > >=20 > > > > + if (symbol) { > > > > + unsigned int count; > > > > + > > > > + count =3D number_of_same_symbols(symbol); > > > > + if (count > 1) { > > > > + /* > > > > + * Users should use ADDR to remove the ambiguity of > > > > + * using KSYM only. > > > > + */ > > > >=20 > > > >=20 > > > >=20 > > > > + ret =3D -EADDRNOTAVAIL; > > > > + > > > > + goto error; > > > > + } else if (count =3D=3D 0) { > > > > + /* > > > > + * We can return ENOENT earlier than when register the > > > > + * kprobe. > > > > + */ > > > > + ret =3D -ENOENT; > > > > + > > > > + goto error; > > > > + } > > > > + } > > > > + > > > >=20 > > > > trace_probe_log_set_index(0); > > > > if (event) { > > > > =09 > > > > ret =3D traceprobe_parse_event_name(&event, &group, gbuf, > > > >=20 > > > > @@ -1699,6 +1741,7 @@ 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 +1752,24 @@ create_local_trace_kprobe(char *func, void > > > > *addr, > > > > unsigned long offs,> > > > >=20 > > > > int ret; > > > > char *event; > > > >=20 > > > > + if (func) { > > > > + unsigned int count; > > > > + > > > > + count =3D number_of_same_symbols(func); > > > > + if (count > 1) > > > > + /* > > > > + * Users should use addr to remove the ambiguity of > > > > + * using func only. > > > > + */ > > > > + return ERR_PTR(-EADDRNOTAVAIL); > > > > + else if (count =3D=3D 0) > > > > + /* > > > > + * We can return ENOENT earlier than when register the > > > > + * kprobe. > > > > + */ > > > > + return ERR_PTR(-ENOENT); > > > > + } > > > > + > > > >=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.