| Message ID | 20191005091614.11635-2-leo.yan@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | perf cs-etm: Support thread stack and callchain | expand |
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 <leo.yan@linaro.org> > --- > 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) 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. Mathieu > { > 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 >
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 <leo.yan@linaro.org> > > --- > > 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) > > 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 > > { > > 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 > >
Hi Leo, Two points here - both related. On Tue, 22 Oct 2019 at 06:10, Leo Yan <leo.yan@linaro.org> 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 <leo.yan@linaro.org> > > > --- > > > 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
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 <leo.yan@linaro.org> 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 <leo.yan@linaro.org> > > > > --- > > > > 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
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) { 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);
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 <leo.yan@linaro.org> --- tools/perf/util/cs-etm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.17.1