Initial support for dumping DWARF corresponding to Swift code

The DWARF data for Swift code has a top-level DW_TAG_module DIE as the
child of the DW_TAG_compile_unit DIE and the parent of the
DW_TAG_subprogram DIEs that dump_syms uses to locate functions.
dump_syms needs to process DW_TAG_module DIEs as introducing nested
scopes to make it work with Swift.

This also reworks demangling to be language-specific, so that the C++
demangler isn't invoked when processing Swift code. The DWARF data for
Swift code presents its mangled names in the same form as used for C++
(DW_AT_MIPS_linkage_name or DW_AT_linkage_name) but the mangling is
Swift-specific (beginning with _T instead of _Z). There is no
programmatic interface to a Swift name demangler as an analogue to C++'s
__cxa_demangle(), so mangled Swift names are exposed as-is. Xcode's
"xcrun swift-demangle" can be used to post-process these mangled Swift
names on macOS.

Support for mangled names presented in a DW_AT_linkage_name attribute,
as used by DWARF 4, is added. This supersedes the earlier use of
DW_AT_MIPS_linkage_name.

BUG=google-breakpad:702,google-breakpad:715
R=ted.mielczarek@gmail.com

Review URL: https://codereview.chromium.org/2147523005 .

1 files changed, 16 insertions, 0 deletions

diff --git a/src/common/language.h b/src/common/language.h
index bbe30334..05786199 100644
--- a/src/common/language.h
+++ b/src/common/language.h
@@ -77,9 +77,25 @@ class Language {
   virtual string MakeQualifiedName (const string &parent_name,
                                     const string &name) const = 0;
 
+  enum DemangleResult {
+    // Demangling was not performed because it’s not appropriate to attempt.
+    kDontDemangle = -1,
+
+    kDemangleSuccess,
+    kDemangleFailure,
+  };
+
+  // Wraps abi::__cxa_demangle() or similar for languages where appropriate.
+  virtual DemangleResult DemangleName(const string& mangled,
+                                      std::string* demangled) const {
+    demangled->clear();
+    return kDontDemangle;
+  }
+
   // Instances for specific languages.
   static const Language * const CPlusPlus,
                         * const Java,
+                        * const Swift,
                         * const Assembler;
 };