Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932744AbcLMBax (ORCPT ); Mon, 12 Dec 2016 20:30:53 -0500 Received: from mail.kernel.org ([198.145.29.136]:54390 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752999AbcLMBat (ORCPT ); Mon, 12 Dec 2016 20:30:49 -0500 Date: Tue, 13 Dec 2016 10:30:39 +0900 From: Masami Hiramatsu To: Marcin Nowakowski Cc: Steven Rostedt , Ingo Molnar , Subject: Re: [PATCH v2 2/2] kprobes/trace: Fix kprobe selftest for newer gcc Message-Id: <20161213103039.d8402249aed7d974c7f1aaee@kernel.org> In-Reply-To: <1481293178-3128-2-git-send-email-marcin.nowakowski@imgtec.com> References: <1481293178-3128-1-git-send-email-marcin.nowakowski@imgtec.com> <1481293178-3128-2-git-send-email-marcin.nowakowski@imgtec.com> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3557 Lines: 112 On Fri, 9 Dec 2016 15:19:38 +0100 Marcin Nowakowski wrote: > Commit 265a5b7ee3eb ("kprobes/trace: Fix kprobe selftest for gcc 4.6") > has added __used attribute to kprobe_trace_selftest_target to ensure > that the method is listed in kallsyms table. > > However, even though the method remains in the kernel image, the actual > call is optimised away as there are no side efects and the return value > is never checked. Nice catch :) > > Add a return value check and a 'noinline' attribute to ensure that an > inlined copy of the method is not used by the caller. Also add checks > that verify that the kprobe was really hit, as at the moment the tests > show positive results despite the test method being optimised away. > > Finally, add __init annotations to find_trace_probe_file() and > kprobe_trace_selftest_target() as they are only called from within an > __init method. Right. Looks good to me. Acked-by: Masami Hiramatsu Thanks! > > Signed-off-by: Marcin Nowakowski > --- > kernel/trace/trace_kprobe.c | 28 +++++++++++++++++++++++----- > 1 file changed, 23 insertions(+), 5 deletions(-) > > v2: no changes > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index a2af1bc..a133ecd 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -1361,18 +1361,18 @@ fs_initcall(init_kprobe_trace); > > > #ifdef CONFIG_FTRACE_STARTUP_TEST > - > /* > * The "__used" keeps gcc from removing the function symbol > - * from the kallsyms table. > + * from the kallsyms table. 'noinline' makes sure that there > + * isn't an inlined version used by the test method below > */ > -static __used int kprobe_trace_selftest_target(int a1, int a2, int a3, > - int a4, int a5, int a6) > +static __used __init noinline int > +kprobe_trace_selftest_target(int a1, int a2, int a3, int a4, int a5, int a6) > { > return a1 + a2 + a3 + a4 + a5 + a6; > } > > -static struct trace_event_file * > +static struct __init trace_event_file * > find_trace_probe_file(struct trace_kprobe *tk, struct trace_array *tr) > { > struct trace_event_file *file; > @@ -1450,12 +1450,25 @@ static __init int kprobe_trace_self_tests_init(void) > > ret = target(1, 2, 3, 4, 5, 6); > > + /* > + * Not expecting an error here, the check is only to prevent the > + * optimizer from removing the call to target() as otherwise there > + * are no side-effects and the call is never performed. > + */ > + if (ret != 21) > + warn++; > + > /* Disable trace points before removing it */ > tk = find_trace_kprobe("testprobe", KPROBE_EVENT_SYSTEM); > if (WARN_ON_ONCE(tk == NULL)) { > pr_warn("error on getting test probe.\n"); > warn++; > } else { > + if (trace_kprobe_nhit(tk) != 1) { > + pr_warn("incorrect number of testprobe hits\n"); > + warn++; > + } > + > file = find_trace_probe_file(tk, top_trace_array()); > if (WARN_ON_ONCE(file == NULL)) { > pr_warn("error on getting probe file.\n"); > @@ -1469,6 +1482,11 @@ static __init int kprobe_trace_self_tests_init(void) > pr_warn("error on getting 2nd test probe.\n"); > warn++; > } else { > + if (trace_kprobe_nhit(tk) != 1) { > + pr_warn("incorrect number of testprobe2 hits\n"); > + warn++; > + } > + > file = find_trace_probe_file(tk, top_trace_array()); > if (WARN_ON_ONCE(file == NULL)) { > pr_warn("error on getting probe file.\n"); > -- > 2.7.4 > -- Masami Hiramatsu