perf python scripting: Fix printable strings in python3 scripts

Hagen reported broken strings in python3 tracepoint scripts:

  make PYTHON=python3
  perf record -e sched:sched_switch -a -- sleep 5
  perf script --gen-script py
  perf script -s ./perf-script.py

  [..]
  sched__sched_switch      7 563231.759525792        0 swapper   prev_comm=bytearray(b'swapper/7\x00\x00\x00\x00\x00\x00\x00'), prev_pid=0, prev_prio=120, prev_state=, next_comm=bytearray(b'mutex-thread-co\x00'),

The problem is in the is_printable_array function that does not take the
zero byte into account and claim such string as not printable, so the
code will create byte array instead of string.

Committer testing:

After this fix:

sched__sched_switch 3 484522.497072626  1158680 kworker/3:0-eve  prev_comm=kworker/3:0, prev_pid=1158680, prev_prio=120, prev_state=I, next_comm=swapper/3, next_pid=0, next_prio=120
Sample: {addr=0, cpu=3, datasrc=84410401, datasrc_decode=N/A|SNP N/A|TLB N/A|LCK N/A, ip=18446744071841817196, period=1, phys_addr=0, pid=1158680, tid=1158680, time=484522497072626, transaction=0, values=[(0, 0)], weight=0}

sched__sched_switch 4 484522.497085610  1225814 perf             prev_comm=perf, prev_pid=1225814, prev_prio=120, prev_state=, next_comm=migration/4, next_pid=30, next_prio=0
Sample: {addr=0, cpu=4, datasrc=84410401, datasrc_decode=N/A|SNP N/A|TLB N/A|LCK N/A, ip=18446744071841817196, period=1, phys_addr=0, pid=1225814, tid=1225814, time=484522497085610, transaction=0, values=[(0, 0)], weight=0}

Fixes: 249de6e074 ("perf script python: Fix string vs byte array resolving")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Hagen Paul Pfeifer <hagen@jauu.net>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200928201135.3633850-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/print_binary.c

@@ -50,7 +50,7 @@ int is_printable_array(char *p, unsigned int len)
 
 	len--;
 
-	for (i = 0; i < len; i++) {
+	for (i = 0; i < len && p[i]; i++) {
 		if (!isprint(p[i]) && !isspace(p[i]))
 			return 0;
 	}