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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A3B3ACA9EAE for ; Wed, 23 Oct 2019 06:49:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6D6D72084C for ; Wed, 23 Oct 2019 06:49:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="GffoRzk8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389378AbfJWGtj (ORCPT ); Wed, 23 Oct 2019 02:49:39 -0400 Received: from mail-qt1-f193.google.com ([209.85.160.193]:34306 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbfJWGtj (ORCPT ); Wed, 23 Oct 2019 02:49:39 -0400 Received: by mail-qt1-f193.google.com with SMTP id e14so11013841qto.1 for ; Tue, 22 Oct 2019 23:49:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=kvpjxtScXgXjfdUkU4TdG5xrgeslRCzjrCl+So6ijK0=; b=GffoRzk85s4gzEnNGrEuNLLealKCdTMGkfhw9aBrWgOECrJwtnhn2eE/n+OnrDy8Jh 5XqxN6+Ho6bL6Ud3oJRhNw1dYIMhP4RNcVCowrIdqFnea904/rJVTtRot4bnX4IS8ncz 0AWx0os2UW6b69sH8hdeaxPKAjQq9WSUqcqcXVV9QHfphDoRDkWQT4ESKlkZwlkIqDKK w8OD90AfYFhmdVrpEARIDEm4oi2uO2dwFAgS7DwG45MIMWN2sr73L4drSuKgtTBa5YOT R1caMRE29agTzgDKaUJHKPyUQj+o0BaJXG5HSMVJcqZCA9s9h/j3PMLxB638q3PFBwtv Ivdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=kvpjxtScXgXjfdUkU4TdG5xrgeslRCzjrCl+So6ijK0=; b=iMdnxewwIOzESFtUQHNt8insnD6hztL7kKD6RZakUhrZUfzqChgGwiKB4LX6FppXRP Jfo/09UJD86If6fIOgZCIoDiHmsxYtQM/b3xZyfO7x11wP7/5HM/pPrXWGkpwJm4mOOu P/wN8o4BzZGVV1QkTQnZzJltieR6MhtYhuQo4+RuFnMmir9LFTu11CixQGA3jqIvYPVf LQfN3YdI2xtL4SFikVNNWr/rymIz/iS1fT5BZONKuUANbce8hg5W9cI+JyIJkBnSoCQ0 TnIz41KNS+QrBGriXo1BN+QQzjZ83qQdAZaGfOEw/KMsKW6QDIxjHPfvuf5C3qUVv49m vCnA== X-Gm-Message-State: APjAAAUXgMeVuCUY0HnQITijbFrV4p1oBs7wTIrch5LxaCjeQUsvsmM0 sbaye1Zq2/6HVI/r6D2eqzhkEA== X-Google-Smtp-Source: APXvYqxSMXYVdzqMGxUGCqPoW6dmW+edXWvsmS8YXC8pKkUTaJq/xBnl3xXbQzGVKbe9WEp/dSPbjQ== X-Received: by 2002:ac8:89c:: with SMTP id v28mr7535979qth.156.1571813377114; Tue, 22 Oct 2019 23:49:37 -0700 (PDT) Received: from leoy-ThinkPad-X240s (li937-157.members.linode.com. [45.56.119.157]) by smtp.gmail.com with ESMTPSA id d126sm8134132qkc.93.2019.10.22.23.49.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 22 Oct 2019 23:49:36 -0700 (PDT) Date: Wed, 23 Oct 2019 14:49:26 +0800 From: Leo Yan To: Mike Leach Cc: Mathieu Poirier , Arnaldo Carvalho de Melo , Suzuki K Poulose , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-arm-kernel , linux-kernel@vger.kernel.org, Coresight ML , Peter Zijlstra , Ingo Molnar Subject: Re: [PATCH v3 1/6] perf cs-etm: Fix unsigned variable comparison to zero Message-ID: <20191023064926.GB29009@leoy-ThinkPad-X240s> References: <20191005091614.11635-1-leo.yan@linaro.org> <20191005091614.11635-2-leo.yan@linaro.org> <20191011201606.GC13688@xps15> <20191022051020.GC32731@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mike, On Wed, Oct 23, 2019 at 12:36:39AM +0100, Mike Leach wrote: > Hi Leo, > > Two points here - both related. > > On Tue, 22 Oct 2019 at 06:10, Leo Yan wrote: > > > > Hi Mathieu, > > > > On Fri, Oct 11, 2019 at 02:16:06PM -0600, Mathieu Poirier wrote: > > > On Sat, Oct 05, 2019 at 05:16:09PM +0800, Leo Yan wrote: > > > > If the u64 variable 'offset' is a negative integer, comparison it with > > > > bigger than zero is always going to be true because it is unsigned. > > > > Fix this by using s64 type for variable 'offset'. > > > > > > > > Signed-off-by: Leo Yan > > > > --- > > > > tools/perf/util/cs-etm.c | 4 ++-- > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > > > > index 4ba0f871f086..4bc2d9709d4f 100644 > > > > --- a/tools/perf/util/cs-etm.c > > > > +++ b/tools/perf/util/cs-etm.c > > > > @@ -940,7 +940,7 @@ u64 cs_etm__last_executed_instr(const struct cs_etm_packet *packet) > > > > static inline u64 cs_etm__instr_addr(struct cs_etm_queue *etmq, > > > > u64 trace_chan_id, > > > > const struct cs_etm_packet *packet, > > > > - u64 offset) > > > > + s64 offset) > > > > Issue 1: > > OK - it appears that cs_etm__instr_addr() is supposed to be returning > the address within the current trace sample of the instruction related > to offset. > For T32 - then if offset < 0, packet->start_addr is returned - not > good but at least within the current trace range > For A32/A64 - if offset < 0 then an address _before_ > packet->start_addr is returned - clearly wrong and possibly a > completely invalid address that was never actually traced. Exactly, if offset < 0 it might output the incorrect trace. > > > In Suzuki's reply there was two choices, 1) move the while(offset > 0) to > > > while (offset) or change the type of @offset to an s64. Here we know offset > > > can't be negative because of the > > > tidq->period_instructions >= etm->instructions_sample_period > > > > > > in function cs_etm__sample(). As such I think option #1 is the right way to > > > deal with this rather than changing the type of the variable. > > > > I took sometime to use formulas to prove that 'offset' is possible to > > be a negative value :) > > > > Just paste the updated commit log at here for review: > > > > Pi: period_instructions > > Ie: instrs_executed > > Io: instrs_over > > Ip: instructions_sample_period > > > > Pi' = Pi + Ie -> New period_instructions equals to the old > > period_instructions + instrs_executed > > Io = Pi' - Ip -> period_instructions - instructions_sample_period > > > > offset = Ie - Io - 1 > > = Ie - (Pi' - Ip) -1 > > = Ie - (Pi + Ie - Ip) -1 > > = Ip - Pi - 1 > > > > In theory, if Ip (instructions_sample_period) is small enough and Pi > > (period_instructions) is bigger than Ip, then it will lead to the > > negative value for 'offset'. > > > > So let's see below command: > > > > perf inject --itrace=i1il128 -i perf.data -o perf.data.new > > > > With this command, 'offset' is very easily to be a negative value when > > handling packets; this is because if use the inject option 'i1', then > > instructions_sample_period equals to 1; so: > > > > offset = 1 - Pi - 1 > > = -Pi > > > > Any Pi bigger than zero leads 'offset' to a negative value. > > > > Thanks, > > Leo Yan > > > > Issue 2: > > Assuming I have understood the logic of this code correctly - there is > an issue were sample_period < period_instructions as you say - > but I believe the problem is in the logic of the sampling function itself. > > Suppose we have a sample_period of 4. > > Now on an initial pass through the function, period_instructions must > be 0. (i.e. none left over from the previous pass.) > Suppose also that the number of instructions executed in this sample > is 10 - thus updating period_instructions. > Therefore: > instr_over = 10 - 4 -> 6 > offset = 10 - 6 - 1 -> 3. > We therefore call cs_etm_instr_addr to find the address an offset of 3 > instructions from the start of the trace sample and synthesize the > sample. > After this we set period_instructions to the instr_over value of 6. > > Next pass, assume 10 instructions in the trace sample again. > period_instructions = 6 + 10 -> 16 > instr_over = 16 - 4 -> 12 > offset = 10 - 12 - 1 -> -3 - the negative value your formulae predict. > > This implies that the sample we want is actually in the previous trace > packet - which I believe is in fact the case - as explained below. > > My reading of the code is that cs_etm__sample() is called once per > trace range packet extracted from the decoder - and a trace range > packet represents N instructions_executed. > Further I am assuming that instructions_sample_period represents the > desired periodicity of the instruction samples - i.e. 1 sample every > instructions_sample_period number of instructions. Good point. Yeah, this is the root cause. > Thus my conclusion here is that where M = instructions_executed + > period_instructions, the function should generate quotient ( M / > instructions_sample_period ) samples and set period_instructions to M > mod instructions_sample_period on exit, ensuring period_instructions > is never larger than the sample_period. Totally agree with this; we should generate synthetic samples without dropping trace data. > i.e. loop to generate multiple samples until instr_over and therefore > the output value of period_instructions is less than the value of > instructions_sample_period - for the example above, with 10 > instructions and a periodicity of 4, we generate 2 samples with a > remainder of 2 instructions carried forwards. > > In short leave offset as unsigned and fix the logic of the > cs_etm__sample() function. Will follow up this suggestion. Very appreciate your time to review and gave out much reasonable solution! Thanks, Leo Yan > > > > { > > > > if (packet->isa == CS_ETM_ISA_T32) { > > > > u64 addr = packet->start_addr; > > > > @@ -1372,7 +1372,7 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, > > > > * sample is reported as though instruction has just been > > > > * executed, but PC has not advanced to next instruction) > > > > */ > > > > - u64 offset = (instrs_executed - instrs_over - 1); > > > > + s64 offset = (instrs_executed - instrs_over - 1); > > > > u64 addr = cs_etm__instr_addr(etmq, trace_chan_id, > > > > tidq->packet, offset); > > > > > > > > -- > > > > 2.17.1 > > > > > > > > -- > Mike Leach > Principal Engineer, ARM Ltd. > Manchester Design Centre. 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[45.56.119.157]) by smtp.gmail.com with ESMTPSA id d126sm8134132qkc.93.2019.10.22.23.49.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 22 Oct 2019 23:49:36 -0700 (PDT) Date: Wed, 23 Oct 2019 14:49:26 +0800 From: Leo Yan To: Mike Leach Subject: Re: [PATCH v3 1/6] perf cs-etm: Fix unsigned variable comparison to zero Message-ID: <20191023064926.GB29009@leoy-ThinkPad-X240s> References: <20191005091614.11635-1-leo.yan@linaro.org> <20191005091614.11635-2-leo.yan@linaro.org> <20191011201606.GC13688@xps15> <20191022051020.GC32731@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191022_234938_844162_15F9C6DD X-CRM114-Status: GOOD ( 36.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Mathieu Poirier , Suzuki K Poulose , Alexander Shishkin , Coresight ML , linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Namhyung Kim , Jiri Olsa , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Mike, On Wed, Oct 23, 2019 at 12:36:39AM +0100, Mike Leach wrote: > Hi Leo, > > Two points here - both related. > > On Tue, 22 Oct 2019 at 06:10, Leo Yan wrote: > > > > Hi Mathieu, > > > > On Fri, Oct 11, 2019 at 02:16:06PM -0600, Mathieu Poirier wrote: > > > On Sat, Oct 05, 2019 at 05:16:09PM +0800, Leo Yan wrote: > > > > If the u64 variable 'offset' is a negative integer, comparison it with > > > > bigger than zero is always going to be true because it is unsigned. > > > > Fix this by using s64 type for variable 'offset'. > > > > > > > > Signed-off-by: Leo Yan > > > > --- > > > > tools/perf/util/cs-etm.c | 4 ++-- > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > > > > index 4ba0f871f086..4bc2d9709d4f 100644 > > > > --- a/tools/perf/util/cs-etm.c > > > > +++ b/tools/perf/util/cs-etm.c > > > > @@ -940,7 +940,7 @@ u64 cs_etm__last_executed_instr(const struct cs_etm_packet *packet) > > > > static inline u64 cs_etm__instr_addr(struct cs_etm_queue *etmq, > > > > u64 trace_chan_id, > > > > const struct cs_etm_packet *packet, > > > > - u64 offset) > > > > + s64 offset) > > > > Issue 1: > > OK - it appears that cs_etm__instr_addr() is supposed to be returning > the address within the current trace sample of the instruction related > to offset. > For T32 - then if offset < 0, packet->start_addr is returned - not > good but at least within the current trace range > For A32/A64 - if offset < 0 then an address _before_ > packet->start_addr is returned - clearly wrong and possibly a > completely invalid address that was never actually traced. Exactly, if offset < 0 it might output the incorrect trace. > > > In Suzuki's reply there was two choices, 1) move the while(offset > 0) to > > > while (offset) or change the type of @offset to an s64. Here we know offset > > > can't be negative because of the > > > tidq->period_instructions >= etm->instructions_sample_period > > > > > > in function cs_etm__sample(). As such I think option #1 is the right way to > > > deal with this rather than changing the type of the variable. > > > > I took sometime to use formulas to prove that 'offset' is possible to > > be a negative value :) > > > > Just paste the updated commit log at here for review: > > > > Pi: period_instructions > > Ie: instrs_executed > > Io: instrs_over > > Ip: instructions_sample_period > > > > Pi' = Pi + Ie -> New period_instructions equals to the old > > period_instructions + instrs_executed > > Io = Pi' - Ip -> period_instructions - instructions_sample_period > > > > offset = Ie - Io - 1 > > = Ie - (Pi' - Ip) -1 > > = Ie - (Pi + Ie - Ip) -1 > > = Ip - Pi - 1 > > > > In theory, if Ip (instructions_sample_period) is small enough and Pi > > (period_instructions) is bigger than Ip, then it will lead to the > > negative value for 'offset'. > > > > So let's see below command: > > > > perf inject --itrace=i1il128 -i perf.data -o perf.data.new > > > > With this command, 'offset' is very easily to be a negative value when > > handling packets; this is because if use the inject option 'i1', then > > instructions_sample_period equals to 1; so: > > > > offset = 1 - Pi - 1 > > = -Pi > > > > Any Pi bigger than zero leads 'offset' to a negative value. > > > > Thanks, > > Leo Yan > > > > Issue 2: > > Assuming I have understood the logic of this code correctly - there is > an issue were sample_period < period_instructions as you say - > but I believe the problem is in the logic of the sampling function itself. > > Suppose we have a sample_period of 4. > > Now on an initial pass through the function, period_instructions must > be 0. (i.e. none left over from the previous pass.) > Suppose also that the number of instructions executed in this sample > is 10 - thus updating period_instructions. > Therefore: > instr_over = 10 - 4 -> 6 > offset = 10 - 6 - 1 -> 3. > We therefore call cs_etm_instr_addr to find the address an offset of 3 > instructions from the start of the trace sample and synthesize the > sample. > After this we set period_instructions to the instr_over value of 6. > > Next pass, assume 10 instructions in the trace sample again. > period_instructions = 6 + 10 -> 16 > instr_over = 16 - 4 -> 12 > offset = 10 - 12 - 1 -> -3 - the negative value your formulae predict. > > This implies that the sample we want is actually in the previous trace > packet - which I believe is in fact the case - as explained below. > > My reading of the code is that cs_etm__sample() is called once per > trace range packet extracted from the decoder - and a trace range > packet represents N instructions_executed. > Further I am assuming that instructions_sample_period represents the > desired periodicity of the instruction samples - i.e. 1 sample every > instructions_sample_period number of instructions. Good point. Yeah, this is the root cause. > Thus my conclusion here is that where M = instructions_executed + > period_instructions, the function should generate quotient ( M / > instructions_sample_period ) samples and set period_instructions to M > mod instructions_sample_period on exit, ensuring period_instructions > is never larger than the sample_period. Totally agree with this; we should generate synthetic samples without dropping trace data. > i.e. loop to generate multiple samples until instr_over and therefore > the output value of period_instructions is less than the value of > instructions_sample_period - for the example above, with 10 > instructions and a periodicity of 4, we generate 2 samples with a > remainder of 2 instructions carried forwards. > > In short leave offset as unsigned and fix the logic of the > cs_etm__sample() function. Will follow up this suggestion. Very appreciate your time to review and gave out much reasonable solution! Thanks, Leo Yan > > > > { > > > > if (packet->isa == CS_ETM_ISA_T32) { > > > > u64 addr = packet->start_addr; > > > > @@ -1372,7 +1372,7 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, > > > > * sample is reported as though instruction has just been > > > > * executed, but PC has not advanced to next instruction) > > > > */ > > > > - u64 offset = (instrs_executed - instrs_over - 1); > > > > + s64 offset = (instrs_executed - instrs_over - 1); > > > > u64 addr = cs_etm__instr_addr(etmq, trace_chan_id, > > > > tidq->packet, offset); > > > > > > > > -- > > > > 2.17.1 > > > > > > > > -- > Mike Leach > Principal Engineer, ARM Ltd. > Manchester Design Centre. UK _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel