python3 fixes and testing support (#1916)

* python3: check ksymname calls with _assert_is_bytes

Fixes a bytes/string concatenation error when get/fix_syscall_fnname is
called from a python3 system.

* python3: use env python invocation in tools

In order to facilitate testing, but not necessarily as an example of
good practice, I am changing the invocation of the test tools to use
`/usr/bin/env python`, so that we can control which python (2 vs 3)
gets invoked for the test. On the buildbots, I plan to add an optional
`ln -s /usr/bin/python3 /usr/local/bin/python` on systems that have
python3-bcc package built. This way, we get more test coverage. Having a
cmake mechanism to enable both python2 and python3 testing could be a
further enhancement.

* tools/memleak: add an explicit stdout.flush to print loop

The stdout flush behavior seems to have changed in python3, breaking one
of the tests. I think it makes sense to flush stdout at the end of each
timed interval loop anyway, so adding that to the tool itself.

* tests: add b'' strings and fix dangling handles

Add b'' strings in a few places in the test tools, and fix one dangling
process handle in the memleak test tool runner.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/python/bcc/__init__.py b/src/python/bcc/__init__.py
index e9802f89..943e1556 100644
--- a/src/python/bcc/__init__.py
+++ b/src/python/bcc/__init__.py
@@ -551,7 +551,7 @@ class BPF(object):
     # would probably lead to error in later API calls.
     def get_syscall_prefix(self):
         for prefix in self._syscall_prefixes:
-            if self.ksymname("{}bpf".format(prefix)) != -1:
+            if self.ksymname(b"%sbpf" % prefix) != -1:
                 return prefix
         return self._syscall_prefixes[0]
 
@@ -559,12 +559,14 @@ class BPF(object):
     # system's syscall prefix. For example, given "clone" the helper would
     # return "sys_clone" or "__x64_sys_clone".
     def get_syscall_fnname(self, name):
+        name = _assert_is_bytes(name)
         return self.get_syscall_prefix() + name
 
     # Given a Kernel function name that represents a syscall but already has a
     # prefix included, transform it to current system's prefix. For example,
     # if "sys_clone" provided, the helper may translate it to "__x64_sys_clone".
     def fix_syscall_fnname(self, name):
+        name = _assert_is_bytes(name)
         for prefix in self._syscall_prefixes:
             if name.startswith(prefix):
                 return self.get_syscall_fnname(name[len(prefix):])