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 <leo....@linaro.org> > --- > 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 ? > + 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 >
