gold 2.20 backport: Don't create unnecessary version symbol

[Ian Lance Taylor-3]

I think Doug's patch to make gold not create an unnecessary version
symbol is appropriate for the 2.20.1 release.  I backported it as
follows.

Ian


2009-11-06  Ian Lance Taylor  <iant@...>

        Bring over from mainline:
        2009-10-16  Doug Kwan  <dougkwan@...>

        * dynobj.cc (Versions::Versions): Initialize version_script_.
        Only insert base version symbol definition for a shared object
        if version script defines any version versions.
        (Versions::define_base_version): New method definition.
        (Versions::add_def): Check that base version is not needed.
        (Versions::add_need): Define base version lazily.
        * dynobj.h (Versions::define_base_version): New method declaration.
        (Versions::needs_base_version_): New data member declaration.



Index: dynobj.cc
===================================================================
RCS file: /cvs/src/src/gold/dynobj.cc,v
retrieving revision 1.44.2.1
diff -p -u -r1.44.2.1 dynobj.cc
--- dynobj.cc 16 Oct 2009 05:51:17 -0000 1.44.2.1
+++ dynobj.cc 7 Nov 2009 02:14:50 -0000
@@ -1300,27 +1300,18 @@ Verneed::write(const Stringpool* dynpool
 Versions::Versions(const Version_script_info& version_script,
                    Stringpool* dynpool)
   : defs_(), needs_(), version_table_(),
-    is_finalized_(false), version_script_(version_script)
+    is_finalized_(false), version_script_(version_script),
+    needs_base_version_(parameters->options().shared())
 {
-  // We always need a base version, so define that first.  Nothing
-  // explicitly declares itself as part of base, so it doesn't need to
-  // be in version_table_.
-  if (parameters->options().shared())
-    {
-      const char* name = parameters->options().soname();
-      if (name == NULL)
- name = parameters->options().output_file_name();
-      name = dynpool->add(name, false, NULL);
-      Verdef* vdbase = new Verdef(name, std::vector<std::string>(),
-                                  true, false, true);
-      this->defs_.push_back(vdbase);
-    }
-
   if (!this->version_script_.empty())
     {
       // Parse the version script, and insert each declared version into
       // defs_ and version_table_.
       std::vector<std::string> versions = this->version_script_.get_versions();
+
+      if (this->needs_base_version_ && !versions.empty())
+ this->define_base_version(dynpool);
+
       for (size_t k = 0; k < versions.size(); ++k)
         {
           Stringpool::Key version_key;
@@ -1350,6 +1341,28 @@ Versions::~Versions()
     delete *p;
 }
 
+// Define the base version of a shared library.  The base version definition
+// must be the first entry in defs_.  We insert it lazily so that defs_ is
+// empty if no symbol versioning is used.  Then layout can just drop the
+// version sections.
+
+void
+Versions::define_base_version(Stringpool* dynpool)
+{
+  // If we do any versioning at all,  we always need a base version, so
+  // define that first.  Nothing explicitly declares itself as part of base,
+  // so it doesn't need to be in version_table_.
+  gold_assert(this->defs_.empty());
+  const char* name = parameters->options().soname();
+  if (name == NULL)
+    name = parameters->options().output_file_name();
+  name = dynpool->add(name, false, NULL);
+  Verdef* vdbase = new Verdef(name, std::vector<std::string>(),
+                              true, false, true);
+  this->defs_.push_back(vdbase);
+  this->needs_base_version_ = false;
+}
+
 // Return the dynamic object which a symbol refers to.
 
 Dynobj*
@@ -1421,7 +1434,10 @@ Versions::add_def(const Symbol* sym, con
       if (parameters->options().shared())
  gold_error(_("symbol %s has undefined version %s"),
    sym->demangled_name().c_str(), version);
-
+      else
+ // We only insert a base version for shared library.
+ gold_assert(!this->needs_base_version_);
+
       // When creating a regular executable, automatically define
       // a new version.
       Verdef* vd = new Verdef(version, std::vector<std::string>(),
@@ -1468,6 +1484,10 @@ Versions::add_need(Stringpool* dynpool,
 
   if (vn == NULL)
     {
+      // Create base version definition lazily for shared library.
+      if (this->needs_base_version_)
+ this->define_base_version(dynpool);
+
       // We have a new filename.
       vn = new Verneed(filename);
       this->needs_.push_back(vn);
Index: dynobj.h
===================================================================
RCS file: /cvs/src/src/gold/dynobj.h,v
retrieving revision 1.32.2.1
diff -p -u -r1.32.2.1 dynobj.h
--- dynobj.h 16 Oct 2009 05:51:17 -0000 1.32.2.1
+++ dynobj.h 7 Nov 2009 02:14:51 -0000
@@ -584,6 +584,10 @@ class Versions
   version_index(const Symbol_table*, const Stringpool*,
  const Symbol* sym) const;
 
+  // Define the base version of a shared library.
+  void
+  define_base_version(Stringpool* dynpool);
+
   // We keep a hash table mapping canonicalized name/version pairs to
   // a version base.
   typedef std::pair<Stringpool::Key, Stringpool::Key> Key;
@@ -616,6 +620,9 @@ class Versions
   bool is_finalized_;
   // Contents of --version-script, if passed, or NULL.
   const Version_script_info& version_script_;
+  // Whether we need to insert a base version.  This is only used for
+  // shared libaries and is cleared when the base version is defined.
+  bool needs_base_version_;
 };
 
 } // End namespace gold.