bcc/python: fix attach kprobe/kretprobe using regex

Attach kprobe/kretprobe using regular expression should fail
explicitly if no functions are traceable. Currently we catch
all exceptions and if no functions are available, program
continue with no BPF programs attached. In this commit, change
this behavior to explicitly report error to user.

Signed-off-by: Hengqi Chen <[email protected]>

src/python/bcc/__init__.py

@@ -782,11 +782,17 @@ def attach_kprobe(self, event=b"", event_off=0, fn_name=b"", event_re=b""):
  if event_re:
  matches = BPF.get_kprobe_functions(event_re)
  self._check_probe_quota(len(matches))
+ failed = 0
+ probes = []
  for line in matches:
  try:
  self.attach_kprobe(event=line, fn_name=fn_name)
  except:
- pass
+ failed += 1
+ probes.append(line)
+ if failed == len(matches):
+ raise Exception("Failed to attach BPF program %s to kprobe %s" %
+ (fn_name, '/'.join(probes)))
  return
 
  self._check_probe_quota(1)
@@ -806,12 +812,19 @@ def attach_kretprobe(self, event=b"", fn_name=b"", event_re=b"", maxactive=0):
 
  # allow the caller to glob multiple functions together
  if event_re:
- for line in BPF.get_kprobe_functions(event_re):
+ matches = BPF.get_kprobe_functions(event_re)
+ failed = 0
+ probes = []
+ for line in matches:
  try:
  self.attach_kretprobe(event=line, fn_name=fn_name,
  maxactive=maxactive)
  except:
- pass
+ failed += 1
+ probes.append(line)
+ if failed == len(matches):
+ raise Exception("Failed to attach BPF program %s to kretprobe %s" %
+ (fn_name, '/'.join(probes)))
  return
 
  self._check_probe_quota(1)