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 .

src/common/language.cc

@@ -34,18 +34,66 @@
 
 #include "common/language.h"
 
+#include <stdlib.h>
+
+#if !defined(__ANDROID__)
+#include <cxxabi.h>
+#endif
+
+#include <limits>
+
+namespace {
+
+string MakeQualifiedNameWithSeparator(const string& parent_name,
+                                      const char* separator,
+                                      const string& name) {
+  if (parent_name.empty()) {
+    return name;
+  }
+
+  return parent_name + separator + name;
+}
+
+}  // namespace
+
 namespace google_breakpad {
 
 // C++ language-specific operations.
 class CPPLanguage: public Language {
  public:
   CPPLanguage() {}
+
   string MakeQualifiedName(const string &parent_name,
                            const string &name) const {
-    if (parent_name.empty())
-      return name;
-    else
-      return parent_name + "::" + name;
+    return MakeQualifiedNameWithSeparator(parent_name, "::", name);
+  }
+
+  virtual DemangleResult DemangleName(const string& mangled,
+                                      std::string* demangled) const {
+#if defined(__ANDROID__)
+    // Android NDK doesn't provide abi::__cxa_demangle.
+    demangled->clear();
+    return kDontDemangle;
+#else
+    int status;
+    char* demangled_c =
+        abi::__cxa_demangle(mangled.c_str(), NULL, NULL, &status);
+
+    DemangleResult result;
+    if (status == 0) {
+      result = kDemangleSuccess;
+      demangled->clear();
+    } else {
+      result = kDemangleFailure;
+      demangled->assign(demangled_c);
+    }
+
+    if (demangled_c) {
+      free(reinterpret_cast<void*>(demangled_c));
+    }
+
+    return result;
+#endif
   }
 };
 
@@ -54,19 +102,45 @@ CPPLanguage CPPLanguageSingleton;
 // Java language-specific operations.
 class JavaLanguage: public Language {
  public:
+  JavaLanguage() {}
+
   string MakeQualifiedName(const string &parent_name,
                            const string &name) const {
-    if (parent_name.empty())
-      return name;
-    else
-      return parent_name + "." + name;
+    return MakeQualifiedNameWithSeparator(parent_name, ".", name);
   }
 };
 
 JavaLanguage JavaLanguageSingleton;
 
+// Swift language-specific operations.
+class SwiftLanguage: public Language {
+ public:
+  SwiftLanguage() {}
+
+  string MakeQualifiedName(const string &parent_name,
+                           const string &name) const {
+    return MakeQualifiedNameWithSeparator(parent_name, ".", name);
+  }
+
+  virtual DemangleResult DemangleName(const string& mangled,
+                                      std::string* demangled) const {
+    // There is no programmatic interface to a Swift demangler. Pass through the
+    // mangled form because it encodes more information than the qualified name
+    // that would have been built by MakeQualifiedName(). The output can be
+    // post-processed by xcrun swift-demangle to transform mangled Swift names
+    // into something more readable.
+    demangled->assign(mangled);
+    return kDemangleSuccess;
+  }
+};
+
+SwiftLanguage SwiftLanguageSingleton;
+
 // Assembler language-specific operations.
 class AssemblerLanguage: public Language {
+ public:
+  AssemblerLanguage() {}
+
   bool HasFunctions() const { return false; }
   string MakeQualifiedName(const string &parent_name,
                            const string &name) const {
@@ -78,6 +152,7 @@ AssemblerLanguage AssemblerLanguageSingleton;
 
 const Language * const Language::CPlusPlus = &CPPLanguageSingleton;
 const Language * const Language::Java = &JavaLanguageSingleton;
+const Language * const Language::Swift = &SwiftLanguageSingleton;
 const Language * const Language::Assembler = &AssemblerLanguageSingleton;
 
 } // namespace google_breakpad