tools/funcslower: fix printing of folded stacks

When trying to print folded stack, funcslower tries to join bytes to a
string. Let's perform that operation with bytes only, and decode
before printing.
Also, decode symbols name before printing for the default stack
format, to avoid unsightly b'xxx' output.

It fixes the following error:

Exception ignored on calling ctypes callback function: <function PerfEventArray._open_perf_buffer.<locals>.raw_cb_ at 0x7f200541e5e0>
Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/bcc/table.py", line 982, in raw_cb_
    callback(cpu, data, size)
  File "/usr/share/bcc/tools/funcslower", line 340, in print_event
    print_stack(event)
  File "/usr/share/bcc/tools/funcslower", line 324, in print_stack
    print("%s %d" % (";".join(line), 1))
TypeError: sequence item 1: expected str instance, bytes found

Signed-off-by: Jerome Marchand <[email protected]>

tools/funcslower.py

@@ -317,17 +317,17 @@ def print_stack(event):
  # print folded stack output
  user_stack = list(user_stack)
  kernel_stack = list(kernel_stack)
- line = [event.comm.decode('utf-8', 'replace')] + \
+ line = [event.comm] + \
  [b.sym(addr, event.tgid_pid) for addr in reversed(user_stack)] + \
  (do_delimiter and ["-"] or []) + \
  [b.ksym(addr) for addr in reversed(kernel_stack)]
- print("%s %d" % (";".join(line), 1))
+ print("%s %d" % (b';'.join(line).decode('utf-8', 'replace'), 1))
  else:
  # print default multi-line stack output.
  for addr in kernel_stack:
- print(" %s" % b.ksym(addr))
+ print(" %s" % b.ksym(addr).decode('utf-8', 'replace'))
  for addr in user_stack:
- print(" %s" % b.sym(addr, event.tgid_pid))
+ print(" %s" % b.sym(addr, event.tgid_pid).decode('utf-8', 'replace'))
 
 def print_event(cpu, data, size):
  event = b["events"].event(data)