Dodji Seketeli 60cdabd931 Bug 18893 - type degradation from dwarf to abixml on libGLU.so ...

abidiff-ing libGLU.so against the result of 'abidw libGLU.so' does not
yield the empty set.  This is because hashing certain types when they
are read (de-serialized) from DWARF doesn't give the same result as
when they are de-serialized from abixml.  I call this type
degradation.  And it leads to spurious comparison differences.

This is due to several issues.

  1/ The logical link between a class declaration and its definition
  -- that is built when reading types from DWARF is not preserved in
  abixml.  So, for example, when a class S refers to itself via a
  pointer to its declaration, that type might hash differently when
  read from DWARF and when read from abixml.  When read from abixml
  it's a pointer to S itself.  But then that 'self' can be a copy of S
  that is defined in another file because abixml doesn't enforce the
  One Definition Rule from C++ either.

  2/ As the result of hashing is kept in a cache for var_decl and
  function_decl, hashing those decl before their types are completely
  built caches a value that becomes wrong when their type become
  completely built.

  3/ In DWARF, a class which has a virtual member function can still
  be considered as being declaration-only.  And its definition can
  come later in the DWARF info.  Our DWARF reader removes the
  "declaration-only" flag from a class as soon as it sees virtual
  member functions in that class; that makes us consider that class as
  a definition.  And then later when we read the real definition of
  the class we have two classes of the same name, with different
  layouts/size in the system.  This leads to spurious comparison
  differences too.

This patch addresses issues 1, 2 and 3.

	* src/abg-dwarf-reader.cc (build_class_type_and_add_to_ir): Do not
	consider that virtual member functions disqualify a class from
	being declaration-only.
	* src/abg-hash.cc (var_decl:#️⃣:operator()): Do not cache the
	result of hashing before we are done building the type of the
	var_decl.
	(function_decl:#️⃣:operator()): Likewise, do not cache the
	result of hashing before we are done building the type of the
	function_decl.
	* src/abg-reader.cc (build_class_decl): Build the link between a
	class declaration and its definition.  If there are several
	definitions of a class in the corpus, keep just one.
	* src/abg-writer.cc (write_class_is_declaration_only): Emit the
	link between a class declaration and its definition.
	(write_class_decl): Emit a class declaration even if it has a
	definition.  The definition is going to be emitted
	separately.
	* tests/data/test-read-dwarf/test14-pr18893.so: New binary test
	input.
	* tests/data/test-read-dwarf/test14-pr18893.so.abi: New test
	reference output.
	* tests/data/Makefile.am: Add the new test input files to source
	distribution.
	* tests/test-read-dwarf.cc (in_out_specs): Run the new tests.
	* tests/data/test-abidiff/test-PR18791-report0.txt: Adjust.
	* tests/data/test-read-dwarf/test9-pr18818-clang.so.abi: Likewise.
	* tests/data/test-read-dwarf/test10-pr18818-gcc.so.abi: Likewise.
	* tests/data/test-read-dwarf/test11-pr18828.so.abi: Likewise.
	* tests/data/test-read-dwarf/test12-pr18844.so.abi: Likewise.
	* tests/data/test-read-dwarf/test13-pr18894.so.abi: Likewise.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>

2015-08-30 17:11:36 +02:00

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