linux-kernel - Re: [PATCH 10/10] perf script python: Fix string vs byte array resolving

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Date:	Tue, 12 Jul 2016 10:11:56 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 10/10] perf script python: Fix string vs byte array
 resolving

On Mon, Jul 11, 2016 at 11:54:52AM -0400, Steven Rostedt wrote:
> On Sun, 10 Jul 2016 13:08:02 +0200
> Jiri Olsa <jolsa@...nel.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@...dmis.org>
> > Reported-and-tested-by: Jiri Pirko <jiri@...lanox.com>
> > Link: http://lkml.kernel.org/n/tip-22f4vhhz5uytegkggy1on8u3@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.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?

ugh, forgot the last 0 byte.. how about attached change?

I wonder it'd be less pain to present all arrays as
PyByteArray, it might be no difference for python
users anyway ;-)

thanks,
jirka


---
diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index 75e9790ebb96..9f810e6c739a 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -390,11 +390,13 @@ static int is_printable_array(char *p, unsigned int len)
 {
 	unsigned int i;
 
-	for (i = 0; i < len; i++)
+	/* Exclude the last zero byte of string.. */
+	for (i = 0; i < len - 1; i++)
 		if (!isprint(p[i]) && !isspace(p[i]))
 			return 0;
 
-	return 1;
+	/* ... and check its presence in the last byte. */
+	return p[i] == 0;
 }
 
 static void python_process_tracepoint(struct perf_sample *sample,