Breakpad Linux dumper: STABS reader incorrectly assumes a single compilation unit

The stabs reading code in google-breakpad incorrectly assumes that the
stabs data is a single compilation unit. Specifically, it ignores
N_UNDF stabs and assumes that all string indices are relative to the
beginning of the .stabstr section.

This is true when linking with the GNU linker by default, because the
GNU linker optimizes stabs debug info. The gold linker does not do
this optimization. It can be disabled when using the GNU linker with
the --traditional-format command line option.

For more details of the problem, see:

http://sourceware.org/bugzilla/show_bug.cgi?id=10338
http://code.google.com/p/google-breakpad/issues/detail?id=359

This patch adds unit tests that reproduce the failure, and fixes the
stabs parser.

a=jimblandy, r=nealsid


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@490 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/linux/stabs_reader.cc

@@ -43,6 +43,8 @@ StabsReader::StabsReader(const uint8_t *stab,    size_t stab_size,
     stabstr_(stabstr),
     stabstr_size_(stabstr_size),
     handler_(handler),
+    string_offset_(0),
+    next_cu_string_offset_(0),
     symbol_(NULL),
     current_source_file_(NULL) { 
   symbols_ = reinterpret_cast<const struct nlist *>(stab);
@@ -50,7 +52,7 @@ StabsReader::StabsReader(const uint8_t *stab,    size_t stab_size,
 }
 
 const char *StabsReader::SymbolString() {
-  ptrdiff_t offset = symbol_->n_un.n_strx;
+  ptrdiff_t offset = string_offset_ + symbol_->n_un.n_strx;
   if (offset < 0 || (size_t) offset >= stabstr_size_) {
     handler_->Warning("symbol %d: name offset outside the string section",
                       symbol_ - symbols_);
@@ -67,6 +69,21 @@ bool StabsReader::Process() {
     if (symbol_->n_type == N_SO) {
       if (! ProcessCompilationUnit())
         return false;
+    } else if (symbol_->n_type == N_UNDF) {
+      // At the head of each compilation unit's entries there is an
+      // N_UNDF stab giving the number of symbols in the compilation
+      // unit, and the number of bytes that compilation unit's strings
+      // take up in the .stabstr section. Each CU's strings are
+      // separate; the n_strx values are offsets within the current
+      // CU's portion of the .stabstr section.
+      //
+      // As an optimization, the GNU linker combines all the
+      // compilation units into one, with a single N_UNDF at the
+      // beginning. However, other linkers, like Gold, do not perform
+      // this optimization.
+      string_offset_ = next_cu_string_offset_;
+      next_cu_string_offset_ = SymbolValue();
+      symbol_++;
     } else
       symbol_++;
   }

src/common/linux/stabs_reader.h

@@ -96,6 +96,13 @@ class StabsReader {
 
   StabsHandler *handler_;
 
+  // The offset of the current compilation unit's strings within stabstr_.
+  size_t string_offset_;
+
+  // The value string_offset_ should have for the next compilation unit,
+  // as established by N_UNDF entries.
+  size_t next_cu_string_offset_;
+
   // The current symbol we're processing.
   const struct nlist *symbol_;
 

src/common/linux/stabs_reader_unittest.cc

@@ -53,6 +53,7 @@ using std::ostringstream;
 using std::string;
 
 using ::testing::_;
+using ::testing::Eq;
 using ::testing::InSequence;
 using ::testing::Return;
 using ::testing::Sequence;
@@ -70,7 +71,8 @@ namespace {
 // sections, and then pass those to StabsReader to look at. The
 // human-readable file is called a "mock stabs file".
 //
-// Each line of a mock stabs file should have the following form:
+// Except for compilation unit boundary lines (described below), each
+// line of a mock stabs file should have the following form:
 //
 //   TYPE OTHER DESC VALUE NAME
 // 
@@ -91,6 +93,10 @@ namespace {
 //   is misleading, but that's how it is.  For SO, this may be a
 //   filename; for FUN, this is the function name, plus type data; and
 //   so on.
+//
+// A compilation unit boundary line has the form:
+//
+//  cu-boundary FILENAME
 
 // I don't know if the whole parser/handler pattern is really worth
 // the bureaucracy in this case.  But just writing it out as
@@ -108,6 +114,11 @@ class MockStabsHandler {
   // stops, and its Process member function returns false.
   virtual bool Entry(enum __stab_debug_code type, char other, short desc,
                      unsigned long value, const string &name) { return true; }
+  // Report a compilation unit boundary whose filename is FILENAME. As
+  // for the Entry function, this should return true to continue
+  // parsing, or false to stop processing.
+  virtual bool CUBoundary(const string &filename) { return true; }
+
   // Report an error in parsing the mock stabs data.  If this returns true,
   // the parser continues; if it returns false, the parser stops and
   // its Process member function returns false.
@@ -159,7 +170,7 @@ bool MockStabsParser::Process() {
   // terminating newline.
   for(;;) {
     string line;
-    std::getline(*stream_, line, '\n');
+    getline(*stream_, line, '\n');
     if (line.empty() && stream_->eof())
       break;
     line_number_++;
@@ -190,6 +201,13 @@ bool MockStabsParser::ParseLine(const string &line) {
   // Parse and validate the stabs type.
   string typeName;
   linestream >> typeName;
+  if (typeName == "cu-boundary") {
+    if (linestream.peek() == ' ')
+      linestream.get();
+    string filename;
+    getline(linestream, filename, '\n');
+    return handler_->CUBoundary(filename);
+  } else {
     StabTypeNameTable::const_iterator typeIt = type_names_.find(typeName);
     if (typeIt == type_names_.end())
       return handler_->Error("%s:%d: unrecognized stab type: %s\n",
@@ -208,6 +226,7 @@ bool MockStabsParser::ParseLine(const string &line) {
     getline(linestream, name, '\n');
     return handler_->Entry(static_cast<__stab_debug_code>(typeIt->second),
                            otherInt, descInt, value, name);
+  }
 }
 
 // A class for constructing .stab sections.
@@ -227,9 +246,15 @@ class StabSection {
   // call to Append.  The caller should initialize the returned entry
   // as needed.
   struct nlist *Append();
+  // Set the first entry's n_desc field to COUNT, and set its n_value field
+  // to STRING_SIZE.
+  void SetHeader(short count, unsigned long string_size);
   // Set SECTION to the contents of a .stab section holding the
   // accumulated list of entries added with Append.
   void GetSection(string *section);
+  // Clear the array, and prepare this StabSection to accumulate a fresh
+  // set of entries.
+  void Clear();
 
  private:
   // The array of stabs entries,
@@ -248,11 +273,23 @@ struct nlist *StabSection::Append() {
   return &entries_[used_++];
 }
 
+void StabSection::SetHeader(short count, unsigned long string_size) {
+  assert(used_ >= 1);
+  entries_[0].n_desc = count;
+  entries_[0].n_value = string_size;
+}
+
 void StabSection::GetSection(string *section) {
   section->assign(reinterpret_cast<char *>(entries_),
                   sizeof(*entries_) * used_);
 }
 
+void StabSection::Clear() {
+  used_ = 0;
+  size_ = 1;
+  entries_ = (struct nlist *) realloc(entries_, sizeof(*entries_) * size_);
+}
+
 // A class for building .stabstr sections.
 // 
 // A .stabstr section is an array of characters containing a bunch of
@@ -273,6 +310,9 @@ class StabstrSection {
   // Set SECTION to the contents of a .stabstr section in which the
   // strings passed to Insert appear at the indices we promised.
   void GetSection(string *section);
+  // Clear the contents of this StabstrSection, and prepare it to
+  // accumulate a new set of strings.
+  void Clear();
  private:
   // Maps from strings to .stabstr indices and back.
   typedef map<string, size_t> StringToIndex;
@@ -317,6 +357,12 @@ void StabstrSection::GetSection(string *section) {
   }
 }
 
+void StabstrSection::Clear() {
+  string_indices_.clear();
+  string_indices_[""] = 0;
+  next_byte_ = 1;
+}
+
 // A mock stabs parser handler class that builds .stab and .stabstr
 // sections.
 class StabsSectionsBuilder: public MockStabsHandler {
@@ -325,13 +371,15 @@ class StabsSectionsBuilder: public MockStabsHandler {
   // and construct .stab and .stabstr sections.  FILENAME should be
   // the name of the mock stabs input file; we use it in error
   // messages.
-  StabsSectionsBuilder(const string &filename):
+  StabsSectionsBuilder(const string &filename)
-      filename_(filename), error_count_(0) { }
+      : filename_(filename), error_count_(0), has_header_(false),
+        entry_count_(0) { }
 
   // Overridden virtual member functions.
   bool Entry(enum __stab_debug_code type, char other, short desc,
              unsigned long value, const string &name);
-  virtual bool Error(const char *format, ...);
+  bool CUBoundary(const string &filename);
+  bool Error(const char *format, ...);
 
   // Set SECTION to the contents of a .stab or .stabstr section
   // reflecting the entries that have been passed to us via Entry.
@@ -339,10 +387,24 @@ class StabsSectionsBuilder: public MockStabsHandler {
   void GetStabstr(string *section);
 
  private:
-  StabSection stab_;                    // stabs entries we've seen
+  // Finish a compilation unit. If there are any entries accumulated in
-  StabstrSection stabstr_;              // and the strings they love
+  // stab_ and stabstr_, add them as a new compilation unit to
+  // finished_cu_stabs_ and finished_cu_stabstr_, and then clear stab_ and
+  // stabstr_.
+  void FinishCU();
+
   const string &filename_;        // input filename, for error messages
   int error_count_;               // number of errors we've seen so far
+
+  // The following members accumulate the contents of a single compilation
+  // unit, possibly headed by an N_UNDF stab.
+  bool has_header_;               // true if we have an N_UNDF header
+  int entry_count_;               // the number of entries we've seen
+  StabSection stab_;              // 'struct nlist' entries
+  StabstrSection stabstr_;        // and the strings they love
+
+  // Accumulated .stab and .stabstr content for all compilation units.
+  string finished_cu_stab_, finished_cu_stabstr_;
 };
 
 bool StabsSectionsBuilder::Entry(enum __stab_debug_code type, char other,
@@ -354,9 +416,48 @@ bool StabsSectionsBuilder::Entry(enum __stab_debug_code type, char other,
   entry->n_desc = desc;
   entry->n_value = value;
   entry->n_un.n_strx = stabstr_.Insert(name);
+  entry_count_++;
   return true;
 }
 
+bool StabsSectionsBuilder::CUBoundary(const string &filename) {
+  FinishCU();
+  // Add a header for the compilation unit.
+  assert(!has_header_);
+  assert(entry_count_ == 0);
+  struct nlist *entry = stab_.Append();
+  entry->n_type = N_UNDF;
+  entry->n_other = 0;
+  entry->n_desc = 0;          // will be set to number of entries
+  entry->n_value = 0;         // will be set to size of .stabstr data
+  entry->n_un.n_strx = stabstr_.Insert(filename);
+  has_header_ = true;
+  // The N_UNDF header isn't included in the symbol count, so we
+  // shouldn't bump entry_count_ here.
+  return true;
+}
+
+void StabsSectionsBuilder::FinishCU() {
+  if (entry_count_ > 0) {
+    // Get the strings first, so we can record their size in the header.
+    string stabstr;
+    stabstr_.GetSection(&stabstr);
+    finished_cu_stabstr_ += stabstr;
+
+    // Initialize our header, if we have one, and extract the .stab data.
+    if (has_header_)
+      stab_.SetHeader(entry_count_, stabstr.size());
+    string stab;
+    stab_.GetSection(&stab);
+    finished_cu_stab_ += stab;
+  }
+
+  stab_.Clear();
+  stabstr_.Clear();
+  has_header_ = false;
+  entry_count_ = 0;
+}
+
 bool StabsSectionsBuilder::Error(const char *format, ...) {
   va_list args;
   va_start(args, format);
@@ -373,11 +474,13 @@ bool StabsSectionsBuilder::Error(const char *format, ...) {
 }
 
 void StabsSectionsBuilder::GetStab(string *section) {
-  stab_.GetSection(section);
+  FinishCU();
+  *section = finished_cu_stab_;
 }
 
 void StabsSectionsBuilder::GetStabstr(string *section) {
-  stabstr_.GetSection(section);
+  FinishCU();
+  *section = finished_cu_stabstr_;
 }
 
 class MockStabsReaderHandler: public StabsHandler {
@@ -428,7 +531,7 @@ static bool ApplyHandlerToMockStabsData(StabsHandler *handler,
   return reader.Process();
 }
 
-TEST(StabsReaderTestCase, MockStabsInput) {
+TEST(StabsReader, MockStabsInput) {
   MockStabsReaderHandler mock_handler;
 
   {
@@ -467,7 +570,7 @@ TEST(StabsReaderTestCase, MockStabsInput) {
                   "common/linux/testdata/stabs_reader_unittest.input1"));
 }
 
-TEST(StabsReaderTestCase, AbruptCU) {
+TEST(StabsReader, AbruptCU) {
   MockStabsReaderHandler mock_handler;
 
   {
@@ -485,7 +588,7 @@ TEST(StabsReaderTestCase, AbruptCU) {
                   "common/linux/testdata/stabs_reader_unittest.input2"));
 }
 
-TEST(StabsReaderTestCase, AbruptFunction) {
+TEST(StabsReader, AbruptFunction) {
   MockStabsReaderHandler mock_handler;
 
   {
@@ -507,7 +610,7 @@ TEST(StabsReaderTestCase, AbruptFunction) {
                   "common/linux/testdata/stabs_reader_unittest.input3"));
 }
 
-TEST(StabsReaderTestCase, NoCU) {
+TEST(StabsReader, NoCU) {
   MockStabsReaderHandler mock_handler;
 
   EXPECT_CALL(mock_handler, StartCompilationUnit(_, _, _))
@@ -521,7 +624,7 @@ TEST(StabsReaderTestCase, NoCU) {
   
 }
 
-TEST(StabsReaderTestCase, NoCUEnd) {
+TEST(StabsReader, NoCUEnd) {
   MockStabsReaderHandler mock_handler;
 
   {
@@ -545,4 +648,36 @@ TEST(StabsReaderTestCase, NoCUEnd) {
   
 }
 
+TEST(StabsReader, MultipleCUs) {
+  MockStabsReaderHandler mock_handler;
+
+  {
+    InSequence s;
+    EXPECT_CALL(mock_handler,
+                StartCompilationUnit(StrEq("antimony"), 0x12, NULL))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, StartFunction(Eq("arsenic"), 0x22))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, EndFunction(0x32))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, EndCompilationUnit(0x32))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler,
+                StartCompilationUnit(StrEq("aluminum"), 0x42, NULL))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, StartFunction(Eq("selenium"), 0x52))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, EndFunction(0x62))
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_handler, EndCompilationUnit(0x62))
+        .WillOnce(Return(true));
+  }
+
+  ASSERT_TRUE(ApplyHandlerToMockStabsData(
+                  &mock_handler,
+                  "common/linux/testdata/stabs_reader_unittest.input6"));
+}
+
+// name duplication
+
 } // anonymous namespace