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[45.79.19.108]) by smtp.gmail.com with ESMTPSA id s17sm9124333otp.36.2019.01.23.15.36.22 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 23 Jan 2019 15:36:25 -0800 (PST) Date: Thu, 24 Jan 2019 07:36:19 +0800 From: Leo Yan To: Mathieu Poirier Cc: Arnaldo Carvalho de Melo , Suzuki K Poulose , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Mike Leach , Robert Walker , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Coresight ML Subject: Re: [PATCH v6 8/8] perf cs-etm: Set sample flags for exception return packet Message-ID: <20190123233619.GA3268@leoy-ThinkPad-X240s> References: <20190119014347.27441-1-leo.yan@linaro.org> <20190119014347.27441-9-leo.yan@linaro.org> <20190123215114.GH620@xps15> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190123215114.GH620@xps15> 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 Mathieu, On Wed, Jan 23, 2019 at 02:51:14PM -0700, Mathieu Poirier wrote: > On Sat, Jan 19, 2019 at 09:43:47AM +0800, Leo Yan wrote: > > When return from exception, we need to distinguish if it's system call > > return or for other type exceptions for setting sample flags. Due to > > the exception return packet doesn't contain exception number, so we > > cannot decide sample flags based on exception number. > > > > On the other hand, the exception return packet is followed by an > > instruction range packet; this range packet deliveries the start address > > after exception handling, we can check if it is a SVC instruction just > > before the start address. If there has one SVC instruction is found > > ahead the return address, this means it's an exception return for system > > call; otherwise it is an normal return for other exceptions. > > > > This patch is to set sample flags for exception return packet, firstly > > it simply set sample flags as PERF_IP_FLAG_INTERRUPT for all exception > > returns since at this point it doesn't know what's exactly the exception > > type. We will defer to decide if it's an exception return for system > > call when the next instruction range packet comes, it checks if there > > has one SVC instruction prior to the start address and if so we will > > change sample flags to PERF_IP_FLAG_SYSCALLRET for system call > > return. > > > > Signed-off-by: Leo Yan > > --- > > tools/perf/util/cs-etm.c | 44 ++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 44 insertions(+) > > > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > > index 052805de6513..7547a7178f46 100644 > > --- a/tools/perf/util/cs-etm.c > > +++ b/tools/perf/util/cs-etm.c > > @@ -1372,6 +1372,20 @@ static int cs_etm__set_sample_flags(struct cs_etm_queue *etmq) > > if (prev_packet->sample_type == CS_ETM_DISCONTINUITY) > > prev_packet->flags |= PERF_IP_FLAG_BRANCH | > > PERF_IP_FLAG_TRACE_BEGIN; > > + > > + /* > > + * If the previous packet is an exception return packet > > + * and the return address just follows SVC instuction, > > + * it needs to calibrate the previous packet sample flags > > + * as PERF_IP_FLAG_SYSCALLRET. > > + */ > > + if (prev_packet->flags == (PERF_IP_FLAG_BRANCH | > > + PERF_IP_FLAG_RETURN | > > + PERF_IP_FLAG_INTERRUPT) && > > Would it make more sense to just look for prev-packet->sample_type == > CS_ETM_EXCEPTION_RET ? We cannot check 'prev-packet->sample_type == CS_ETM_EXCEPTION_RET', since CS_ETM_EXCEPTION_RET is associated to its previous instruction range packet but not a standalone instruction range packet, we don't swap for exception and exception return packets, 'prev_packet' is pointed to the previous instruction range packet at here. This is why we need to use 'prev_packet->flags' but not 'prev_packet->sample_type' as checking condition. Thanks, Leo Yan > > + cs_etm__is_svc_instr(etmq, packet, packet->start_addr)) > > + prev_packet->flags = PERF_IP_FLAG_BRANCH | > > + PERF_IP_FLAG_RETURN | > > + PERF_IP_FLAG_SYSCALLRET; > > break; > > case CS_ETM_DISCONTINUITY: > > /* > > @@ -1422,6 +1436,36 @@ static int cs_etm__set_sample_flags(struct cs_etm_queue *etmq) > > prev_packet->flags = packet->flags; > > break; > > case CS_ETM_EXCEPTION_RET: > > + /* > > + * When the exception return packet is inserted, since > > + * exception return packet is not used standalone for > > + * generating samples and it's affiliation to the previous > > + * instruction range packet; so set previous range packet > > + * flags to tell perf it is an exception return branch. > > + * > > + * The exception return can be for either system call or > > + * other exception types; unfortunately the packet doesn't > > + * contain exception type related info so we cannot decide > > + * the exception type purely based on exception return packet. > > + * If we record the exception number from exception packet and > > + * reuse it for excpetion return packet, this is not reliable > > + * due the trace can be discontinuity or the interrupt can > > + * be nested, thus the recorded exception number cannot be > > + * used for exception return packet for these two cases. > > + * > > + * For exception return packet, we only need to distinguish the > > + * packet is for system call or for other types. Thus the > > + * decision can be deferred when receive the next packet which > > + * contains the return address, based on the return address we > > + * can read out the previous instruction and check if it's a > > + * system call instruction and then calibrate the sample flag > > + * as needed. > > + */ > > + if (prev_packet->sample_type == CS_ETM_RANGE) > > + prev_packet->flags = PERF_IP_FLAG_BRANCH | > > + PERF_IP_FLAG_RETURN | > > + PERF_IP_FLAG_INTERRUPT; > > + break; > > case CS_ETM_EMPTY: > > default: > > break; > > -- > > 2.17.1 > >