perf test: Fix failure of 'evsel-tp-sched' test on s390

perf test: Fix failure of 'evsel-tp-sched' test on s390

Commit 489338a717a0 ("perf tests evsel-tp-sched: Fix bitwise operator")
causes test case 14 "Parse sched tracepoints fields" to fail on s390.

This test succeeds on x86.

In fact this test now fails on all architectures with type char treated
as type unsigned char.

The root cause is the signed-ness of character arrays in the tracepoints
sched_switch for structure members prev_comm and next_comm.

On s390 the output of:

 [root@m35lp76 perf]# cat /sys/kernel/debug/tracing/events/sched/sched_switch/format
 name: sched_switch
 ID: 287
 format:
   field:unsigned short common_type; offset:0; size:2;	signed:0;
   ...
   field:char prev_comm[16]; offset:8; size:16;	signed:0;
   ...
   field:char next_comm[16]; offset:40; size:16; signed:0;

reveals the character arrays prev_comm and next_comm are per
default unsigned char and have values in the range of 0..255.

On x86 both fields are signed as this output shows:
 [root@f29]# cat /sys/kernel/debug/tracing/events/sched/sched_switch/format
 name: sched_switch
 ID: 287
 format:
   field:unsigned short common_type; offset:0; size:2;	signed:0;
   ...
   field:char prev_comm[16]; offset:8; size:16;	signed:1;
   ...
   field:char next_comm[16]; offset:40; size:16; signed:1;

and the character arrays prev_comm and next_comm are per default signed
char and have values in the range of -1..127.  The implementation of
type char is architecture specific.

Since the character arrays in both tracepoints sched_switch and
sched_wakeup should contain ascii characters, simply omit the check for
signedness in the test case.

Output before:

  [root@m35lp76 perf]# ./perf test -F 14
  14: Parse sched tracepoints fields                        :
  --- start ---
  sched:sched_switch: "prev_comm" signedness(0) is wrong, should be 1
  sched:sched_switch: "next_comm" signedness(0) is wrong, should be 1
  sched:sched_wakeup: "comm" signedness(0) is wrong, should be 1
  ---- end ----
  14: Parse sched tracepoints fields                        : FAILED!
  [root@m35lp76 perf]#

Output after:

  [root@m35lp76 perf]# ./perf test -Fv 14
  14: Parse sched tracepoints fields                        :
  --- start ---
  ---- end ----
  Parse sched tracepoints fields: Ok
  [root@m35lp76 perf]#

Fixes: 489338a717a0 ("perf tests evsel-tp-sched: Fix bitwise operator")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20190219153639.31267-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>