tools/stack_decode.py: Migrate to Python 3

Signed-off-by: Luke Shumaker <lukeshu@datawire.io>

tools/stack_decode.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 
 # Call addr2line as needed to resolve addresses in a stack trace. The addresses
 # will be replaced if they can be resolved into file and line numbers. The
@@ -11,7 +11,6 @@
 # In each case this script will add file and line information to any backtrace log
 # lines found and echo back all non-Backtrace lines untouched.
 
-from __future__ import print_function
 import collections
 import re
 import subprocess
@@ -57,7 +56,7 @@ def decode_stacktrace_log(object_file, input_source):
 #
 # Returns list of result lines
 def run_addr2line(obj_file, addr_to_resolve):
-  return subprocess.check_output(["addr2line", "-Cpie", obj_file, addr_to_resolve])
+  return subprocess.check_output(["addr2line", "-Cpie", obj_file, addr_to_resolve]).decode('utf-8')
 
 
 # Because of how bazel compiles, addr2line reports file names that begin with
@@ -73,7 +72,7 @@ def trim_proc_cwd(file_and_line_number):
     decode_stacktrace_log(sys.argv[2], sys.stdin)
     sys.exit(0)
   elif len(sys.argv) > 1:
-    rununder = subprocess.Popen(sys.argv[1:], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    rununder = subprocess.Popen(sys.argv[1:], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
     decode_stacktrace_log(sys.argv[1], rununder.stdout)
     rununder.wait()
     sys.exit(rununder.returncode)  # Pass back test pass/fail result