Don't demangle Rust symbols by default, but allow linking to rust-demangle.

The Rust compiler uses GCC C++ name mangling, but it has another layer of
encoding so abi::cxa_demangle doesn't produce great results. This patch
changes dump_syms to dump unmangled names by default so that consumers can
demangle them after-the-fact.

It also adds a tiny bit of support for linking against a Rust library I wrote
that can demangle Rust symbols nicely:
https://github.com/luser/rust-demangle-capi

BUG=

Change-Id: I63a425035ebb7ac516f067fed2aa782849ea9604
Reviewed-on: https://chromium-review.googlesource.com/402308
Reviewed-by: Mark Mentovai <mark@chromium.org>

src/common/dwarf/dwarf2enums.h

@@ -544,6 +544,7 @@ enum DwarfLanguage
     DW_LANG_ObjC_plus_plus           =0x0011,
     DW_LANG_UPC                      =0x0012,
     DW_LANG_D                        =0x0013,
+    DW_LANG_Rust                     =0x001c,
     DW_LANG_Swift                    =0x001e,
     // Implementation-defined language code range.
     DW_LANG_lo_user = 0x8000,

src/common/dwarf_cu_to_module.cc

@@ -777,6 +777,10 @@ void DwarfCUToModule::SetLanguage(DwarfLanguage language) {
       cu_context_->language = Language::Swift;
       break;
 
+    case dwarf2reader::DW_LANG_Rust:
+      cu_context_->language = Language::Rust;
+      break;
+
     // DWARF has no generic language code for assembly language; this is
     // what the GNU toolchain uses.
     case dwarf2reader::DW_LANG_Mips_Assembler:

src/common/dwarf_cu_to_module_unittest.cc

@@ -1205,6 +1205,7 @@ TEST_F(Specifications, Function) {
 }
 
 TEST_F(Specifications, MangledName) {
+  // Language defaults to C++, so no need to set it here.
   PushLine(0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL, "line-file", 54883661);
 
   StartCU();
@@ -1221,6 +1222,53 @@ TEST_F(Specifications, MangledName) {
                0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL);
 }
 
+TEST_F(Specifications, MangledNameSwift) {
+  // Swift mangled names should pass through untouched.
+  SetLanguage(dwarf2reader::DW_LANG_Swift);
+  PushLine(0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL, "line-file", 54883661);
+  StartCU();
+  const string kName = "_TFC9swifttest5Shape17simpleDescriptionfS0_FT_Si";
+  DeclarationDIE(&root_handler_, 0xcd3c51b946fb1eeeLL,
+                 dwarf2reader::DW_TAG_subprogram, "declaration-name",
+                 kName);
+  DefinitionDIE(&root_handler_, dwarf2reader::DW_TAG_subprogram,
+                0xcd3c51b946fb1eeeLL, "",
+                0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL);
+  root_handler_.Finish();
+
+  TestFunctionCount(1);
+  TestFunction(0, kName,
+               0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL);
+}
+
+TEST_F(Specifications, MangledNameRust) {
+  SetLanguage(dwarf2reader::DW_LANG_Rust);
+  PushLine(0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL, "line-file", 54883661);
+
+  StartCU();
+  const string kName = "_ZN14rustc_demangle8demangle17h373defa94bffacdeE";
+  DeclarationDIE(&root_handler_, 0xcd3c51b946fb1eeeLL,
+                 dwarf2reader::DW_TAG_subprogram, "declaration-name",
+                 kName);
+  DefinitionDIE(&root_handler_, dwarf2reader::DW_TAG_subprogram,
+                0xcd3c51b946fb1eeeLL, "",
+                0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL);
+  root_handler_.Finish();
+
+  TestFunctionCount(1);
+  TestFunction(0,
+#ifndef HAVE_RUST_DEMANGLE
+               // Rust mangled names should pass through untouched if not
+               // using rust-demangle.
+               kName,
+#else
+               // If rust-demangle is available this should be properly
+               // demangled.
+               "rustc_demangle::demangle",
+#endif
+               0x93cd3dfc1aa10097ULL, 0x0397d47a0b4ca0d4ULL);
+}
+
 TEST_F(Specifications, MemberFunction) {
   PushLine(0x3341a248634e7170ULL, 0x5f6938ee5553b953ULL, "line-file", 18116691);
 

src/common/language.cc

@@ -40,6 +40,10 @@
 #include <cxxabi.h>
 #endif
 
+#if defined(HAVE_RUST_DEMANGLE)
+#include <rust_demangle.h>
+#endif
+
 #include <limits>
 
 namespace {
@@ -136,6 +140,40 @@ class SwiftLanguage: public Language {
 
 SwiftLanguage SwiftLanguageSingleton;
 
+// Rust language-specific operations.
+class RustLanguage: public Language {
+ public:
+  RustLanguage() {}
+
+  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 {
+    // Rust names use GCC C++ name mangling, but demangling them with
+    // abi_demangle doesn't produce stellar results due to them having
+    // another layer of encoding.
+    // If callers provide rustc-demangle, use that.
+#if defined(HAVE_RUST_DEMANGLE)
+    char* rust_demangled = rust_demangle(mangled.c_str());
+    if (rust_demangled == nullptr) {
+      return kDemangleFailure;
+    }
+    demangled->assign(rust_demangled);
+    free_rust_demangled_name(rust_demangled);
+#else
+    // Otherwise, pass through the mangled name so callers can demangle
+    // after the fact.
+    demangled->assign(mangled);
+#endif
+    return kDemangleSuccess;
+  }
+};
+
+RustLanguage RustLanguageSingleton;
+
 // Assembler language-specific operations.
 class AssemblerLanguage: public Language {
  public:
@@ -153,6 +191,7 @@ AssemblerLanguage AssemblerLanguageSingleton;
 const Language * const Language::CPlusPlus = &CPPLanguageSingleton;
 const Language * const Language::Java = &JavaLanguageSingleton;
 const Language * const Language::Swift = &SwiftLanguageSingleton;
+const Language * const Language::Rust = &RustLanguageSingleton;
 const Language * const Language::Assembler = &AssemblerLanguageSingleton;
 
 } // namespace google_breakpad

src/common/language.h

@@ -96,6 +96,7 @@ class Language {
   static const Language * const CPlusPlus,
                         * const Java,
                         * const Swift,
+                        * const Rust,
                         * const Assembler;
 };