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SubjectRe: [PATCH 10/10] perf script python: Fix string vs byte array resolving
On Sun, 10 Jul 2016 13:08:02 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> Jirka reported that python code returns all arrays as strings.
> This makes impossible to get all items for byte array tracepoint
> field containing 0x00 value item.
>
> Fixing this by scanning full length of the array and returning
> it as PyByteArray object in case non printable byte is found.
>
> Cc: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
> Reported-and-tested-by: Jiri Pirko <jiri@mellanox.com>
> Link: http://lkml.kernel.org/n/tip-22f4vhhz5uytegkggy1on8u3@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> .../util/scripting-engines/trace-event-python.c | 34 ++++++++++++++++++----
> 1 file changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
> index ff134700bf30..75e9790ebb96 100644
> --- a/tools/perf/util/scripting-engines/trace-event-python.c
> +++ b/tools/perf/util/scripting-engines/trace-event-python.c
> @@ -386,6 +386,16 @@ exit:
> return pylist;
> }
>
> +static int is_printable_array(char *p, unsigned int len)
> +{
> + unsigned int i;
> +
> + for (i = 0; i < len; i++)
> + if (!isprint(p[i]) && !isspace(p[i]))
> + return 0;

I believe this will return the wrong result if you pass in a string
that has '\0' in it. Try it out:

char a[] = "hello";

printf("a=%s is %d\n", a, is_printable_array(a, sizeof(a)));

and see what you get?

-- Steve

> +
> + return 1;
> +}
>
> static void python_process_tracepoint(struct perf_sample *sample,
> struct perf_evsel *evsel,
> @@ -457,14 +467,26 @@ static void python_process_tracepoint(struct perf_sample *sample,
> pydict_set_item_string_decref(dict, "common_callchain", callchain);
> }
> for (field = event->format.fields; field; field = field->next) {
> - if (field->flags & FIELD_IS_STRING) {
> - int offset;
> + unsigned int offset, len;
> + unsigned long long val;
> +
> + if (field->flags & FIELD_IS_ARRAY) {
> + offset = field->offset;
> + len = field->size;
> if (field->flags & FIELD_IS_DYNAMIC) {
> - offset = *(int *)(data + field->offset);
> + val = pevent_read_number(scripting_context->pevent,
> + data + offset, len);
> + offset = val;
> + len = offset >> 16;
> offset &= 0xffff;
> - } else
> - offset = field->offset;
> - obj = PyString_FromString((char *)data + offset);
> + }
> + if (field->flags & FIELD_IS_STRING &&
> + is_printable_array(data + offset, len)) {
> + obj = PyString_FromString((char *) data + offset);
> + } else {
> + obj = PyByteArray_FromStringAndSize((const char *) data + offset, len);
> + field->flags &= ~FIELD_IS_STRING;
> + }
> } else { /* FIELD_IS_NUMERIC */
> obj = get_field_numeric_entry(event, field, data);
> }

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