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=-6.9 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 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 CB9C8CA9EA0 for ; Tue, 22 Oct 2019 23:36:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B1962064B for ; Tue, 22 Oct 2019 23:36:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="F2/piHAo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389719AbfJVXgw (ORCPT ); Tue, 22 Oct 2019 19:36:52 -0400 Received: from mail-qt1-f193.google.com ([209.85.160.193]:33427 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729635AbfJVXgv (ORCPT ); Tue, 22 Oct 2019 19:36:51 -0400 Received: by mail-qt1-f193.google.com with SMTP id r5so29611378qtd.0 for ; Tue, 22 Oct 2019 16:36:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=cUuaR4LyEZB38AH7m3cbUEf4VRX283gO52TBH9+80dI=; b=F2/piHAoTO7ug6OtJnSE79CpcKBwRl9rSGdZTxaQzEpA1nQxNP64hIRCi1dDz1xGRH w9ShBQeoZN28WWXjblAvLRfr3s1xZWwGj4lSoHOj8fEpwc27CmC76TsHzORWrrWT/2vl nYt9gjpdENbQb+R1mrbrFHIZadSUTPxok49gRK6iJL30FhKwzcB8FBSZQk9hrK4NcXDh K8xkZ39jxIssT54yraW3PZ0p8202PxjXlwxDdCLwjcGY7KpQma5YqmQ44Qo9HIb5OeEJ 4OAYo5QFimFQ7nbAftHrNad1nxG5ZnE2zpLypJBNk40bRF5IYCQabzU8/NnW3cczbcf1 WiLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=cUuaR4LyEZB38AH7m3cbUEf4VRX283gO52TBH9+80dI=; b=SrP6hkdVjaTdWiMSsdseoYLJTpSDv+naEDk6St+c+PEETvVKz88U334LT0SOvOEl+C sQcWklH2UtruL97NgjdJ0TYDYnEYwrU1Hv4ZuIb1c/oJWcmRnGtwq51cJciQdnWo7Tc7 XdoN1iyP8YlUeq1wdfc0gCrO+DTl/V0MQ7/+YIQ0rvUzHjtFA/UmsJgXOydR6daCSZhe Q9dnaCB4QF25B9lYasSAcB1jKMDHYGOSwG23crkEFLVo3tam/fcJbGujn/IJDkLsD2Wm ra/6X3TlsoAYoGYxXE8uVemwMYJZMEKo4PdZM+RR9LvRynbSCcyewv7bYPSQTCHy6ena CBhQ== X-Gm-Message-State: APjAAAXkujnEorehCmpUXQkcq5bGQW5RfprYkXLQ4BplbR0U1IoCSd5q RCTJZ+9VlZQ6IkjAANIEOR8Z2YlrEBXq6uXJkGcRsA== X-Google-Smtp-Source: APXvYqyP1T3mL5FaCeP16Y0+8KcxclZeem3fvNnJ5akb5TBXmPv5Jq1OOkgEMXg0LAZzOkxVOa9UVXEUV/siORLWkKs= X-Received: by 2002:ac8:72ce:: with SMTP id o14mr6479979qtp.62.1571787410354; Tue, 22 Oct 2019 16:36:50 -0700 (PDT) MIME-Version: 1.0 References: <20191005091614.11635-1-leo.yan@linaro.org> <20191005091614.11635-2-leo.yan@linaro.org> <20191011201606.GC13688@xps15> <20191022051020.GC32731@leoy-ThinkPad-X240s> In-Reply-To: <20191022051020.GC32731@leoy-ThinkPad-X240s> From: Mike Leach Date: Wed, 23 Oct 2019 00:36:39 +0100 Message-ID: Subject: Re: [PATCH v3 1/6] perf cs-etm: Fix unsigned variable comparison to zero To: Leo Yan 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. 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. 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. Regards Mike > > > { > > > 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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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=cUuaR4LyEZB38AH7m3cbUEf4VRX283gO52TBH9+80dI=; b=LsRuToyZHzTe5V4Ex6PeyHnrQl7c81tSCMdzKPavwycvKGVOdjE/FA33FLIDX2d09M v2+gp4XLkTM1Xqrwr+DrdTPLbGQP+tcu0RQL1Z9taK0gAZC+P+TZpGaAhMB66DgC11e8 GbHLKSl/kKCmVYD1+YRo8ge+LzLZHDYzL4eNrdVreEalDAyyLX2OjTMKHYvKNH3rTBlO nuql4x4I/R4JQqFtByfe7xiS9KMbw7UYO6pMAY6NHPqeN9zXCaqtB4X+sp3nQApuOolK ajE98N2gVF0NI/I2aiGFpY2PEcrehA28OxJfaC2TbLqfCfJNq5lwJynMV5Cr3t68gY3l KLBg== X-Gm-Message-State: APjAAAWHHyFC+k5hKZbvwG+qvakvvnoOH4S04LKg/xovdvzfrTx41zuV gbIi2VaD6KUPhsXI2wAURugL44h3Nc7e0dqeVuHfFw== X-Google-Smtp-Source: APXvYqyP1T3mL5FaCeP16Y0+8KcxclZeem3fvNnJ5akb5TBXmPv5Jq1OOkgEMXg0LAZzOkxVOa9UVXEUV/siORLWkKs= X-Received: by 2002:ac8:72ce:: with SMTP id o14mr6479979qtp.62.1571787410354; Tue, 22 Oct 2019 16:36:50 -0700 (PDT) MIME-Version: 1.0 References: <20191005091614.11635-1-leo.yan@linaro.org> <20191005091614.11635-2-leo.yan@linaro.org> <20191011201606.GC13688@xps15> <20191022051020.GC32731@leoy-ThinkPad-X240s> In-Reply-To: <20191022051020.GC32731@leoy-ThinkPad-X240s> From: Mike Leach Date: Wed, 23 Oct 2019 00:36:39 +0100 Message-ID: Subject: Re: [PATCH v3 1/6] perf cs-etm: Fix unsigned variable comparison to zero To: Leo Yan X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191022_163654_359382_69B432B1 X-CRM114-Status: GOOD ( 29.93 ) 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 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. > > 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. 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. 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. Regards Mike > > > { > > > 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