Improve COFF/PE linker garbage collection by preventing the removal of sections containing exported symbols.

PR ld/19803
	* ldlang.c (lang_add_gc_name): New function.  Adds the provided
	symbol name to the list of gc symbols.
	(lang_process): Call lang_add_gc_name with entry_symbol_default if
	entry_symbol.name is NULL.  Use lang_add_gc_name to add the init
	and fini function names.
	* pe-dll.c (process_def_file_and_drectve): Add exported names to
	the gc symbol list.
	* testsuite/ld-pe/pr19803.s: Do not export _testval symbol.
	* testsuite/ld-pe/pr19803.d: Tweak expected output.

ld/ChangeLog

@@ -1,3 +1,16 @@
+2016-03-22  Nick Clifton  <nickc@redhat.com>
+
+	PR ld/19803
+	* ldlang.c (lang_add_gc_name): New function.  Adds the provided
+	symbol name to the list of gc symbols.
+	(lang_process): Call lang_add_gc_name with entry_symbol_default if
+	entry_symbol.name is NULL.  Use lang_add_gc_name to add the init
+	and fini function names.
+	* pe-dll.c (process_def_file_and_drectve): Add exported names to
+	the gc symbol list.
+	* testsuite/ld-pe/pr19803.s: Do not export _testval symbol.
+	* testsuite/ld-pe/pr19803.d: Tweak expected output.
+
 2016-03-22  Nick Clifton  <nickc@redhat.com>
 
 	* configure: Regenerate.

ld/ldlang.c

@@ -6699,6 +6699,23 @@ lang_list_remove_tail (lang_statement_list_type *destlist,
 }
 #endif /* ENABLE_PLUGINS */
 
+/* Add NAME to the list of garbage collection entry points.  */
+
+void
+lang_add_gc_name (const char * name)
+{
+  struct bfd_sym_chain *sym;
+
+  if (name == NULL)
+    return;
+
+  sym = (struct bfd_sym_chain *) stat_alloc (sizeof (*sym));
+
+  sym->next = link_info.gc_sym_list;
+  sym->name = name;
+  link_info.gc_sym_list = sym;
+}
+
 void
 lang_process (void)
 {
@@ -6781,6 +6798,9 @@ lang_process (void)
     }
 #endif /* ENABLE_PLUGINS */
 
+  /* Make sure that nobody has tried to add a symbol to this list before now.  */
+  ASSERT (link_info.gc_sym_list == NULL);
+
   link_info.gc_sym_list = &entry_symbol;
 
   if (entry_symbol.name == NULL)
@@ -6790,37 +6810,16 @@ lang_process (void)
       /* entry_symbol is normally initialied by a ENTRY definition in the
 	 linker script or the -e command line option.  But if neither of
 	 these have been used, the target specific backend may still have
-	 provided an entry symbol via a call to lang_default_entry()o.
+	 provided an entry symbol via a call to lang_default_entry().
 	 Unfortunately this value will not be processed until lang_end()
 	 is called, long after this function has finished.  So detect this
 	 case here and add the target's entry symbol to the list of starting
 	 points for garbage collection resolution.  */
-      if (entry_symbol_default != NULL)
-	{
-	  struct bfd_sym_chain *sym
-	    = (struct bfd_sym_chain *) stat_alloc (sizeof (*sym));
-	  sym->next = link_info.gc_sym_list;
-	  sym->name = entry_symbol_default;
-	  link_info.gc_sym_list = sym;
-	}
+      lang_add_gc_name (entry_symbol_default);
     }
 
- if (link_info.init_function != NULL)
-    {
-      struct bfd_sym_chain *sym
-	= (struct bfd_sym_chain *) stat_alloc (sizeof (*sym));
-      sym->next = link_info.gc_sym_list;
-      sym->name = link_info.init_function;
-      link_info.gc_sym_list = sym;
-    }
-  if (link_info.fini_function != NULL)
-    {
-      struct bfd_sym_chain *sym
-	= (struct bfd_sym_chain *) stat_alloc (sizeof (*sym));
-      sym->next = link_info.gc_sym_list;
-      sym->name = link_info.fini_function;
-      link_info.gc_sym_list = sym;
-    }
+  lang_add_gc_name (link_info.init_function);
+  lang_add_gc_name (link_info.fini_function);
 
   ldemul_after_open ();
   if (config.map_file != NULL)

ld/ldlang.h

@@ -693,4 +693,7 @@ lang_ld_feature (char *);
 extern void
 lang_print_memory_usage (void);
 
+extern void
+lang_add_gc_name (const char *);
+
 #endif

ld/pe-dll.c

@@ -897,6 +897,9 @@ process_def_file_and_drectve (bfd *abfd ATTRIBUTE_UNUSED, struct bfd_link_info *
       char *int_name = pe_def_file->exports[i].internal_name;
       char *name;
 
+      /* PR 19803: Make sure that any exported symbol does not get garbage collected.  */
+      lang_add_gc_name (int_name);
+
       name = xmalloc (strlen (int_name) + 2);
       if (pe_details->underscored && int_name[0] != '@')
 	{

ld/testsuite/ld-pe/pr19803.d

@@ -1,17 +1,13 @@
 #ld: -shared --out-implib dx.dll.a --gc-sections
 #objdump: --syms
-#notarget: mcore-* arm-epoc-pe
+#notarget: mcore-*
 #
-# Check that the target specific entry symbol _DllMainCRTStartup is still
+# The MCORE-PE target does not support -shared.
+#
+# Check that the target specific entry symbol *Startup is still
 # a defined (sec > 0), public (scl == 2) symbol, even after garbage
 # collection.
-#
-# Check that the symbol _testval is undefined (sec == 0) and hidden
-# (scl == 106) in the output.  It should have been changed to this state when
-# garbage collection was performed.
 
-#...
-.*\(sec  0\)\(fl 0x00\)\(ty   0\)\(scl 106\) \(nx 0\) 0x0+000 _testval
 #...
 .*\(sec  1\)\(fl 0x00\)\(ty   0\)\(scl   2\) \(nx 0\) 0x0+000 .*Startup.*
 #pass

ld/testsuite/ld-pe/pr19803.s

@@ -8,7 +8,6 @@ DllMainCRTStartup:
 	nop
 
 	.section .rdata,"dr"
-        .globl  _testval
 _testval:
         .long   1
         .long   2