Breakpad DWARF: Add support for DWARF 4 attribute forms.

This patch allows Breakpad's DWARF reader to at least read or skip
attributes using the new forms defined in version 4 of the DWARF
specification, instead of crashing.

Attributes encoded using DW_FORM_flag_present, DW_FORM_sec_offset, and
DW_FORM_exprloc should work fine now. However, compilation units using
DW_FORM_ref_sig8 to refer to types in .debug_types will need further work
to support. (GCC 4.6.2 does not emit .debug_types sections.)

Specifically:

- dwarf2reader::DwarfForm gets new values.
- dwarf2reader::Dwarf2Handler and dwarf2reader::DIEHandler get new handler
  methods, named ProcessAttributeSignature, for DW_FORM_ref_sig8 attributes.
- dwarf2reader::CompilationUnit reads DW_FORM_ref_sig8 attributes, and
  passes them to ProcessAttributeSignature. It also gets support for
  DW_FORM_sec_offset, DW_FORM_exprloc, and DW_FORM_flag_present, using the
  existing appropriate ProcessAttribute* methods.
- dwarf2reader::DIEDispatcher passes through ProcessAttributeSignature
  attributes to its DIEHandler.
- Unit tests are updated.

a=jimb, r=ted.mielczarek
Review URL: http://breakpad.appspot.com/343003/


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@912 4c0a9323-5329-0410-9bdc-e9ce6186880e

1 files changed, 9 insertions, 0 deletions

diff --git a/src/common/dwarf/dwarf2reader.h b/src/common/dwarf/dwarf2reader.h
index c43bb93b..cd61fb55 100644
--- a/src/common/dwarf/dwarf2reader.h
+++ b/src/common/dwarf/dwarf2reader.h
@@ -393,6 +393,15 @@ class Dwarf2Handler {
                                       enum DwarfForm form,
                                       const std::string& data) { }
 
+  // Called when we have an attribute whose value is the 64-bit signature
+  // of a type unit in the .debug_types section. OFFSET is the offset of
+  // the DIE whose attribute we're reporting. ATTR and FORM are the
+  // attribute's name and form. SIGNATURE is the type unit's signature.
+  virtual void ProcessAttributeSignature(uint64 offset,
+                                         enum DwarfAttribute attr,
+                                         enum DwarfForm form,
+                                         uint64 signature) { }
+
   // Called when finished processing the DIE at OFFSET.
   // Because DWARF2/3 specifies a tree of DIEs, you may get starts
   // before ends of the previous DIE, as we process children before