[RFC][PATCH] fix Read_symbols datarace

[Evgeniy Dushistov]

After update to gcc 4.9.2, link of my project failed,
because of ld.gold crash.
I reproduce this problem:
https://sourceware.org/bugzilla/show_bug.cgi?id=17538                                                                                          

Today I dig into this, and see that problem in
that multiply threads run
Read_symbols::do_read_symbols
which call
Plugin_manager::claim_file
which call
this->objects_.push_back

without any sync, and so std::vector was modified
in many threads without any locks, which of course
cause crashes.

Attached patch fix problem for me.
Comments?

-- 
/Evgeniy
-------------- next part --------------
diff --git a/gold/plugin.cc b/gold/plugin.cc
index 0339d42..4b0f3cf 100644
--- a/gold/plugin.cc
+++ b/gold/plugin.cc
@@ -427,6 +427,7 @@ Plugin_manager::~Plugin_manager()
        ++obj)
     delete *obj;
   this->objects_.clear();
+  delete this->lock_;
 }
 
 // Load all plugin libraries.
@@ -447,6 +448,10 @@ Pluginobj*
 Plugin_manager::claim_file(Input_file* input_file, off_t offset,
                            off_t filesize, Object* elf_object)
 {
+  bool lock_initialized = this->initialize_lock_.initialize();
+
+  gold_assert(lock_initialized);
+  Hold_lock hl(*this->lock_);
   if (this->in_replacement_phase_)
     return NULL;
 
diff --git a/gold/plugin.h b/gold/plugin.h
index 9ef2812..174e81d 100644
--- a/gold/plugin.h
+++ b/gold/plugin.h
@@ -134,7 +134,7 @@ class Plugin_manager
       in_claim_file_handler_(false),
       options_(options), workqueue_(NULL), task_(NULL), input_objects_(NULL),
       symtab_(NULL), layout_(NULL), dirpath_(NULL), mapfile_(NULL),
-      this_blocker_(NULL), extra_search_path_()
+      this_blocker_(NULL), extra_search_path_(), lock_(NULL), initialize_lock_(&lock_)
   { this->current_ = plugins_.end(); }
 
   ~Plugin_manager();
@@ -376,6 +376,8 @@ class Plugin_manager
   // An extra directory to seach for the libraries passed by
   // add_input_library.
   std::string extra_search_path_;
+  Lock *lock_;
+  Initialize_lock initialize_lock_;
 };