From: Anders Dellien <anders@andersdellien.se>
Date: Thu, 20 Dec 2018 13:21:35 +0000 (+0100)
Subject: Simplify handling of null DIEs (#209)
X-Git-Tag: v0.26~30
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=5f9416fa6b6da2b4a7b5ed7305d012ab71b1fb30;p=pyelftools.git

Simplify handling of null DIEs (#209)

The code that is intended to coalesce null DIEs into the DIE that
precedes them does not do that and is actually not needed as the
'unflattening' procedure takes care of any unexpected null DIEs.

Also added a unit test for verifying the DIE size calculation.
---

diff --git a/elftools/dwarf/die.py b/elftools/dwarf/die.py
index 546d000..5d3ad99 100755
--- a/elftools/dwarf/die.py
+++ b/elftools/dwarf/die.py
@@ -188,19 +188,6 @@ class DIE(object):
                 raw_value=raw_value,
                 offset=attr_offset)
 
-        # Count and then consume any null termination bytes to avoid wrong die
-        # size calculation.
-        num_zero_terminators = 0
-        with preserve_stream_pos(self.stream):
-            while True:
-                if self.stream.read(1) == 0:
-                    num_zero_terminators += 1
-                else:
-                    break
-        if num_zero_terminators > 0:
-            # There was at least one zero termination -> consume all of them.
-            self.stream.read(num_zero_terminators)
-
         self.size = self.stream.tell() - self.offset
 
     def _translate_attr_value(self, form, raw_value):
diff --git a/test/test_die_size.py b/test/test_die_size.py
new file mode 100644
index 0000000..7579ce2
--- /dev/null
+++ b/test/test_die_size.py
@@ -0,0 +1,32 @@
+#------------------------------------------------------------------------------
+# elftools tests
+#
+# Anders Dellien (anders@andersdellien.se)
+# This code is in the public domain
+#------------------------------------------------------------------------------
+import unittest
+import os
+
+from elftools.elf.elffile import ELFFile
+
+class TestDieSize(unittest.TestCase):
+    """ This test verifies that null DIEs are treated correctly - i.e.
+        removed when we 'unflatten' the linear list and build a tree.
+        The test file contains a CU with two non-null DIEs (both three bytes big),
+        where the second one is followed by three null DIEs.
+        We verify that the null DIEs are discarded and that the length of the second DIE
+        does not include the null entries that follow it.
+    """
+    def test_die_size(self):
+        with open(os.path.join('test',
+                               'testfiles_for_unittests', 'trailing_null_dies.elf'),
+                  'rb') as f:
+            elffile = ELFFile(f)
+            self.assertTrue(elffile.has_dwarf_info())
+            dwarfinfo = elffile.get_dwarf_info()
+            for CU in dwarfinfo.iter_CUs():
+                 for child in CU.get_top_DIE().iter_children():
+                     self.assertEquals(child.size, 3)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/test/testfiles_for_unittests/trailing_null_dies.elf b/test/testfiles_for_unittests/trailing_null_dies.elf
new file mode 100644
index 0000000..1bc7f5e
Binary files /dev/null and b/test/testfiles_for_unittests/trailing_null_dies.elf differ