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SubjectRe: [PATCH 2/7] perf trace: Correctly handle arrays
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On Thu, 2010-05-13 at 16:03 +1000, Ian Munsie wrote:
> From: Ian Munsie <imunsie@au1.ibm.com>
>
> Previously, perf was assuming that an array from an ftrace event was an
> array of longs, which will not always be the case. Additionally,
> long_size is not even being initialised, so it would fail to read the
> data and would erroneously report that the array was filled with zeroes.
>
> This patch adds two extra entries into the field structure - arraylen
> and elementsize, so that the code can easily look them up instead of
> assuming that the elements are long_size. The element size is currently
> derived by the size of the entire array and the number of elements
> within the array.
>
> This problem can be demonstrated with:
> perf record -e raw_syscalls:sys_enter -a sleep 0.1
> perf trace
>

I'm added this to trace-cmd too.

> Without this patch, output similar to the following is produced:
> perf-4355 [004] 1871.504685: sys_enter: NR 319 (0, 0, 0, 0, 0, 0)
> perf-4355 [004] 1871.504723: sys_enter: NR 3 (0, 0, 0, 0, 0, 0)
> perf-4355 [004] 1871.504733: sys_enter: NR 204 (0, 0, 0, 0, 0, 0)
>
> After applying this patch, the output looks like:
> perf-4355 [004] 1871.504685: sys_enter: NR 319 (10247ac0, ffffffff, 5, ffffffff, 0, 107a80d8)
> perf-4355 [004] 1871.504723: sys_enter: NR 3 (a, ffb6fcf0, 20, ffffffff, 0, 10112c20)
> perf-4355 [004] 1871.504733: sys_enter: NR 204 (a, 4, 800, 6, 0, 10112c20)
>
> Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
> ---
> tools/perf/util/trace-event-parse.c | 11 ++++++++++-
> tools/perf/util/trace-event.h | 2 ++
> 2 files changed, 12 insertions(+), 1 deletions(-)
>
> diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c
> index 8f470f6..f360f75 100644
> --- a/tools/perf/util/trace-event-parse.c
> +++ b/tools/perf/util/trace-event-parse.c
> @@ -852,6 +852,9 @@ static int event_read_fields(struct event *event, struct format_field **fields)
> field->flags |= FIELD_IS_ARRAY;
>
> type = read_token(&token);
> + if (test_type(type, EVENT_ITEM))
> + goto fail;

Note this will incorrectly fail on:

field:__data_loc char[] name;

-- Steve

> + field->arraylen = strtoul(token, NULL, 0);
> while (strcmp(token, "]") != 0) {
> if (last_type == EVENT_ITEM &&
> type == EVENT_ITEM)
> @@ -971,6 +974,11 @@ static int event_read_fields(struct event *event, struct format_field **fields)
>
> free_token(token);
>
> + if (field->flags & FIELD_IS_ARRAY)
> + field->elementsize = field->size / field->arraylen;
> + else
> + field->elementsize = field->size;
> +
> *fields = field;
> fields = &field->next;
>
> @@ -2101,7 +2109,8 @@ static unsigned long long eval_num_arg(void *data, int size,
> }
> right = eval_num_arg(data, size, event, arg->op.right);
> val = read_size(data + larg->field.field->offset +
> - right * long_size, long_size);
> + right * larg->field.field->elementsize,
> + larg->field.field->elementsize);
> break;
> }
> default_op:
> diff --git a/tools/perf/util/trace-event.h b/tools/perf/util/trace-event.h
> index 406d452..cc58a19 100644
> --- a/tools/perf/util/trace-event.h
> +++ b/tools/perf/util/trace-event.h
> @@ -40,6 +40,8 @@ struct format_field {
> char *name;
> int offset;
> int size;
> + unsigned int arraylen;
> + unsigned int elementsize;
> unsigned long flags;
> };
>




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