Demangle C++ symbols in stack traces for Linux.

My first Chromium linux build greeted me with a backtrace of mangled symbols
(FWIW, my /dev/shm permission was wrong). That made me write this patch.

BEFORE:

../sconsbuild/Debug/base_unittests(_ZN10StackTraceC1Ev+0x20) [0x817795e]
../sconsbuild/Debug/base_unittests(_ZN30StackTrace_OutputToStream_Test8TestBodyEv+0x18) [0x805fc98]
../sconsbuild/Debug/base_unittests(_ZN7testing4Test3RunEv+0x7e) [0x82005ea]

AFTER:

../sconsbuild/Debug/base_unittests(StackTrace::StackTrace()+0x20) [0x817778c]
../sconsbuild/Debug/base_unittests(StackTrace_OutputToStream_Test::TestBody()+0x18) [0x805fc98]
../sconsbuild/Debug/base_unittests(testing::Test::Run()+0x7e) [0x8200786]

BUG=none
TEST=manually tested. also ran base_unittests

Review URL: http://codereview.chromium.org/267074
Patch from Satoru Takabayashi <satorux@gmail.com>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@28940 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 74 insertions, 2 deletions

diff --git a/base/debug_util_posix.cc b/base/debug_util_posix.cc
index 4b79d73..20916a0 100644
--- a/base/debug_util_posix.cc
+++ b/base/debug_util_posix.cc
@@ -13,6 +13,12 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#if defined(__GLIBCXX__)
+#include <cxxabi.h>
+#endif
+
+#include <string>
+
 #if defined(OS_MACOSX)
 #include <AvailabilityMacros.h>
 #endif
@@ -25,6 +31,63 @@
 #include "base/scoped_ptr.h"
 #include "base/string_piece.h"
 
+namespace {
+// The prefix used for mangled symbols, per the Itanium C++ ABI:
+// http://www.codesourcery.com/cxx-abi/abi.html#mangling
+const char kMangledSymbolPrefix[] = "_Z";
+
+// Characters that can be used for symbols, generated by Ruby:
+// (('a'..'z').to_a+('A'..'Z').to_a+('0'..'9').to_a + ['_']).join
+const char kSymbolCharacters[] =
+    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";
+
+// Demangles C++ symbols in the given text. Example:
+//
+// "sconsbuild/Debug/base_unittests(_ZN10StackTraceC1Ev+0x20) [0x817778c]"
+// =>
+// "sconsbuild/Debug/base_unittests(StackTrace::StackTrace()+0x20) [0x817778c]"
+void DemangleSymbols(std::string* text) {
+#if defined(__GLIBCXX__)
+
+  std::string::size_type search_from = 0;
+  while (search_from < text->size()) {
+    // Look for the start of a mangled symbol, from search_from.
+    std::string::size_type mangled_start =
+        text->find(kMangledSymbolPrefix, search_from);
+    if (mangled_start == std::string::npos) {
+      break;  // Mangled symbol not found.
+    }
+
+    // Look for the end of the mangled symbol.
+    std::string::size_type mangled_end =
+        text->find_first_not_of(kSymbolCharacters, mangled_start);
+    if (mangled_end == std::string::npos) {
+      mangled_end = text->size();
+    }
+    std::string mangled_symbol =
+        text->substr(mangled_start, mangled_end - mangled_start);
+
+    // Try to demangle the mangled symbol candidate.
+    int status = 0;
+    scoped_ptr_malloc<char> demangled_symbol(
+        abi::__cxa_demangle(mangled_symbol.c_str(), NULL, 0, &status));
+    if (status == 0) {  // Demangling is successful.
+      // Remove the mangled symbol.
+      text->erase(mangled_start, mangled_end - mangled_start);
+      // Insert the demangled symbol.
+      text->insert(mangled_start, demangled_symbol.get());
+      // Next time, we'll start right after the demangled symbol we inserted.
+      search_from = mangled_start + strlen(demangled_symbol.get());
+    } else {
+      // Failed to demangle.  Retry after the "_Z" we just found.
+      search_from = mangled_start + 2;
+    }
+  }
+
+#endif  // defined(__GLIBCXX__)
+}
+}  // namespace
+
 // static
 bool DebugUtil::SpawnDebuggerOnProcess(unsigned /* process_id */) {
   NOTIMPLEMENTED();
@@ -159,7 +222,9 @@ void StackTrace::OutputToStream(std::ostream* os) {
   } else {
     (*os) << "Backtrace:\n";
     for (int i = 0; i < count_; ++i) {
-      (*os) << "\t" << trace_symbols.get()[i] << "\n";
+      std::string trace_symbol(trace_symbols.get()[i]);
+      DemangleSymbols(&trace_symbol);
+      (*os) << "\t" << trace_symbol << "\n";
     }
   }
 }
diff --git a/base/debug_util_unittest.cc b/base/debug_util_unittest.cc
index 01551d0..b9300a4 100644
--- a/base/debug_util_unittest.cc
+++ b/base/debug_util_unittest.cc
@@ -49,7 +49,14 @@ TEST(StackTrace, OutputToStream) {
       << "Expected to find start in backtrace:\n"
       << backtrace_message;
 
-#else  // defined(OS_MACOSX)
+#elif defined(__GLIBCXX__)
+
+  // Expect a demangled symbol.
+  EXPECT_TRUE(backtrace_message.find("testing::Test::Run()") !=
+              std::string::npos)
+      << "Expected a demangled symbol in backtrace:\n"
+      << backtrace_message;
+#else  // defined(__GLIBCXX__)
 
   // Expect to at least find main.
   EXPECT_TRUE(backtrace_message.find("main") != std::string::npos)