Breakpad Linux dumper: Tolerate STABS data from code linked with --gc-sections.

Programs compiled with -ffunction-sections -Wl,--gc-sections may have
SO entries for the start of the compilation unit whose addresses are
zero, even when the compilation unit contains non-omitted functions at
non-zero addresses. The breakpad dumper should not assume that the
compilation unit starting address is always non-zero.

a=jimblandy, r=nealsid


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@542 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/linux/dump_stabs.cc

@@ -58,7 +58,8 @@ static string Demangle(const string &mangled) {
 
 bool DumpStabsHandler::StartCompilationUnit(const char *name, uint64_t address,
                                             const char *build_directory) {
-  assert(!comp_unit_base_address_);
+  assert(!in_compilation_unit_);
+  in_compilation_unit_ = true;
   current_source_file_name_ = name;
   current_source_file_ = module_->FindFile(name);
   comp_unit_base_address_ = address;
@@ -67,7 +68,8 @@ bool DumpStabsHandler::StartCompilationUnit(const char *name, uint64_t address,
 }
 
 bool DumpStabsHandler::EndCompilationUnit(uint64_t address) {
-  assert(comp_unit_base_address_);
+  assert(in_compilation_unit_);
+  in_compilation_unit_ = false;
   comp_unit_base_address_ = 0;
   current_source_file_ = NULL;
   current_source_file_name_ = NULL;

src/common/linux/dump_stabs.h

@@ -63,6 +63,7 @@ class DumpStabsHandler: public google_breakpad::StabsHandler {
   // store it all in MODULE.
   DumpStabsHandler(Module *module) :
       module_(module),
+      in_compilation_unit_(false),
       comp_unit_base_address_(0),
       current_function_(NULL),
       current_source_file_(NULL),
@@ -109,6 +110,11 @@ class DumpStabsHandler: public google_breakpad::StabsHandler {
   // finding the next object.
   vector<Module::Address> boundaries_;
 
+  // True if we are currently within a compilation unit: we have gotten a
+  // StartCompilationUnit call, but no matching EndCompilationUnit call
+  // yet. We use this for sanity checks.
+  bool in_compilation_unit_;
+
   // The base address of the current compilation unit.  We use this to
   // recognize functions we should omit from the symbol file.  (If you
   // know the details of why we omit these, please patch this

src/common/linux/dump_stabs_unittest.cc

@@ -157,6 +157,22 @@ TEST(FunctionNames, Mangled) {
   ASSERT_EQ(0U, function->lines.size());
 }
 
+// The GNU toolchain can omit functions that are not used; however,
+// when it does so, it doesn't clean up the debugging information that
+// refers to them. In STABS, this results in compilation units whose
+// SO addresses are zero.
+TEST(Omitted, Function) {
+  Module m("name", "os", "arch", "id");
+  DumpStabsHandler h(&m);
+
+  // The StartCompilationUnit and EndCompilationUnit calls may both have an
+  // address of zero if the compilation unit has had sections removed.
+  EXPECT_TRUE(h.StartCompilationUnit("compilation-unit", 0, "build-directory"));
+  EXPECT_TRUE(h.StartFunction("function", 0x2a133596));
+  EXPECT_TRUE(h.EndFunction(0));
+  EXPECT_TRUE(h.EndCompilationUnit(0));
+}
+
 // TODO --- if we actually cared about STABS. Even without these we've
 // got full coverage of non-failure source lines in dump_stabs.cc.