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);2.17.1