Detect if num field is valid on v1.0 version.

In Android P, the version field did not get incremented properly in
all places. So if a file with a v1.0 version is found, do a further check
to verify if the num field is really valid.

Test: Verified that a file with v1.0 gets checked and the valid num field
Test: is set correctly.
Test: Verified that a file with v1.1 automatically gets num field set to
Test: valid.
Change-Id: I7f828294c833e334cad76a866bbaa1d78ac02cfb
Merged-In: I7f828294c833e334cad76a866bbaa1d78ac02cfb
(cherry picked from commit b558fe4d53)

scripts/native_heapdump_viewer.py

@@ -117,11 +117,52 @@ def GetVersion(native_heap):
       return m.group('version')
   return None
 
+def NumFieldValid(native_heap):
+  """Determine if the num field is valid.
+
+  Malloc debug for N incorrectly set the num field to the number of
+  backtraces instead of the number of allocations with the same size and
+  backtrace. Read the file and if at least three lines all have the field
+  set to the number of backtraces values, then consider this generated by
+  the buggy malloc debug and indicate the num field is not valid.
+
+  Returns:
+    True if the num field is valid.
+    False if the num field is not valid and should be ignored.
+  """
+
+  re_backtrace = re.compile("Backtrace\s+size:\s+(?P<backtrace_size>\d+)")
+
+  re_line = re.compile("z\s+(?P<zygote>\d+)\s+sz\s+(?P<size>\d+)\s+num\s+(?P<num_allocations>\d+)")
+  matched = 0
+  backtrace_size = 0
+  for line in open(native_heap, "r"):
+    if backtrace_size == 0:
+      m = re_backtrace.match(line)
+      if m:
+        backtrace_size = int(m.group('backtrace_size'))
+    parts = line.split()
+    if len(parts) > 7 and parts[0] == "z" and parts[2] == "sz":
+      m = re_line.match(line)
+      if m:
+        num_allocations = int(m.group('num_allocations'))
+        if num_allocations == backtrace_size:
+          # At least three lines must match this pattern before
+          # considering this the old buggy version of malloc debug.
+          matched += 1
+          if matched == 3:
+            return False
+        else:
+          return True
+  return matched == 0
+
 version = GetVersion(native_heap)
 if not version or version == "v1.0":
   # Version v1.0 was produced by a buggy version of malloc debug where the
   # num field was set incorrectly.
-  num_field_valid = False
+  # Unfortunately, Android P produced a v1.0 version that does set the
+  # num field. Do one more check to see if this is the broken version.
+  num_field_valid = NumFieldValid(native_heap)
 else:
   num_field_valid = True