From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752308AbbGMPYo (ORCPT ); Mon, 13 Jul 2015 11:24:44 -0400 Received: from smtprelay0089.hostedemail.com ([216.40.44.89]:39623 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751267AbbGMPYn (ORCPT ); Mon, 13 Jul 2015 11:24:43 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1542:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2892:3138:3139:3140:3141:3142:3354:3622:3865:3866:3867:3868:3870:3871:4250:4321:4605:5007:6120:6261:7875:7901:7903:7904:8603:8660:8784:9010:10004:10400:10848:10967:11026:11232:11473:11658:11914:12043:12438:12517:12519:12555:12740:13148:13161:13229:13230:13255:14093:14097:21060:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: rings65_bbd6e9f30035 X-Filterd-Recvd-Size: 3588 Date: Mon, 13 Jul 2015 11:24:39 -0400 From: Steven Rostedt To: AKASHI Takahiro Cc: catalin.marinas@arm.com, will.deacon@arm.com, jungseoklee85@gmail.com, olof@lixom.net, broonie@kernel.org, david.griego@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 1/3] ftrace: adjust a function's pc to search for in check_stack() for arm64 Message-ID: <20150713112439.079d275d@gandalf.local.home> In-Reply-To: <1436765375-7119-2-git-send-email-takahiro.akashi@linaro.org> References: <1436765375-7119-1-git-send-email-takahiro.akashi@linaro.org> <1436765375-7119-2-git-send-email-takahiro.akashi@linaro.org> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.28; 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 On Mon, 13 Jul 2015 14:29:33 +0900 AKASHI Takahiro wrote: > Ftace's stack tracer on arm64 returns wrong information about call stacks: > > Depth Size Location (50 entries) > ----- ---- -------- > 0) 5256 0 notifier_call_chain+0x30/0x94 > 1) 5256 0 ftrace_call+0x0/0x4 > 2) 5256 0 notifier_call_chain+0x2c/0x94 > 3) 5256 0 raw_notifier_call_chain+0x34/0x44 > 4) 5256 0 timekeeping_update.constprop.9+0xb8/0x114 > 5) 5256 0 update_wall_time+0x408/0x6dc > > Most of 'Size' fields are unexpectedly zero. > > This is because stack tracer fails to recognize each function's stack frame > in check_stack(). Stack tracer searches for a function's pc in the stack > based on the list returned by save_stack_trace(), but save_stack_trace() on > arm64 does not return the exact return address saved in a stack frame, but > a value decrmented by 4 (which means a branch instruction's address). > This behavior was introduced by > commit e306dfd06fcb ("ARM64: unwind: Fix PC calculation") > > So the matching doesn't succeed in most cases. > > This problem can be fixed either by > a) reverting the commit above > b) adding an arm64-specific hack to check_patch() > > This patch does b). > > Signed-off-by: AKASHI Takahiro > --- > kernel/trace/trace_stack.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c > index 3f34496..7086fc3 100644 > --- a/kernel/trace/trace_stack.c > +++ b/kernel/trace/trace_stack.c > @@ -143,7 +143,11 @@ check_stack(unsigned long ip, unsigned long *stack) > p = start; > > for (; p < top && i < max_stack_trace.nr_entries; p++) { > +#ifdef CONFIG_ARM64 > + if (*p == (stack_dump_trace[i] + 4)) { > +#else > if (*p == stack_dump_trace[i]) { > +#endif Instead of the ugly #ifdef in this code, please add a macro FTRACE_STACK_FRAME_OFFSET Then in include/linux/ftrace.h have: #ifndef FTRACE_STACK_FRAME_OFFSET # define FTRACE_STACK_FRAME_OFFSET 0 #endif And in arch/arm64/include/asm/ftrace.h #define FTRACE_STACK_FRAME_OFFSET 4 And then just do: if (*p == (stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET)) { -- Steve > this_size = stack_dump_index[i++] = > (top - p) * sizeof(unsigned long); > found = 1; From mboxrd@z Thu Jan 1 00:00:00 1970 From: rostedt@goodmis.org (Steven Rostedt) Date: Mon, 13 Jul 2015 11:24:39 -0400 Subject: [RFC 1/3] ftrace: adjust a function's pc to search for in check_stack() for arm64 In-Reply-To: <1436765375-7119-2-git-send-email-takahiro.akashi@linaro.org> References: <1436765375-7119-1-git-send-email-takahiro.akashi@linaro.org> <1436765375-7119-2-git-send-email-takahiro.akashi@linaro.org> Message-ID: <20150713112439.079d275d@gandalf.local.home> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 13 Jul 2015 14:29:33 +0900 AKASHI Takahiro wrote: > Ftace's stack tracer on arm64 returns wrong information about call stacks: > > Depth Size Location (50 entries) > ----- ---- -------- > 0) 5256 0 notifier_call_chain+0x30/0x94 > 1) 5256 0 ftrace_call+0x0/0x4 > 2) 5256 0 notifier_call_chain+0x2c/0x94 > 3) 5256 0 raw_notifier_call_chain+0x34/0x44 > 4) 5256 0 timekeeping_update.constprop.9+0xb8/0x114 > 5) 5256 0 update_wall_time+0x408/0x6dc > > Most of 'Size' fields are unexpectedly zero. > > This is because stack tracer fails to recognize each function's stack frame > in check_stack(). Stack tracer searches for a function's pc in the stack > based on the list returned by save_stack_trace(), but save_stack_trace() on > arm64 does not return the exact return address saved in a stack frame, but > a value decrmented by 4 (which means a branch instruction's address). > This behavior was introduced by > commit e306dfd06fcb ("ARM64: unwind: Fix PC calculation") > > So the matching doesn't succeed in most cases. > > This problem can be fixed either by > a) reverting the commit above > b) adding an arm64-specific hack to check_patch() > > This patch does b). > > Signed-off-by: AKASHI Takahiro > --- > kernel/trace/trace_stack.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c > index 3f34496..7086fc3 100644 > --- a/kernel/trace/trace_stack.c > +++ b/kernel/trace/trace_stack.c > @@ -143,7 +143,11 @@ check_stack(unsigned long ip, unsigned long *stack) > p = start; > > for (; p < top && i < max_stack_trace.nr_entries; p++) { > +#ifdef CONFIG_ARM64 > + if (*p == (stack_dump_trace[i] + 4)) { > +#else > if (*p == stack_dump_trace[i]) { > +#endif Instead of the ugly #ifdef in this code, please add a macro FTRACE_STACK_FRAME_OFFSET Then in include/linux/ftrace.h have: #ifndef FTRACE_STACK_FRAME_OFFSET # define FTRACE_STACK_FRAME_OFFSET 0 #endif And in arch/arm64/include/asm/ftrace.h #define FTRACE_STACK_FRAME_OFFSET 4 And then just do: if (*p == (stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET)) { -- Steve > this_size = stack_dump_index[i++] = > (top - p) * sizeof(unsigned long); > found = 1;