gold, ld: Implement -z start-stop-visibility=... option.

gold/
	Implement -z start-stop-visibility=... option.
	* options.h (class General_options): Handle -z start-stop-visibility=.
	(General_options::start_stop_visibility_enum): New public method.
	(General_options::set_start_stop_visibility_enum): New private method.
	(General_options::start_stop_visibility_enum_): New private member.
	* options.cc (General_options::General_options): Add initializer.
	(General_options::finalize): Set this->start_stop_visibility_enum_
	from string value.
	* layout.cc (Layout::define_section_symbols): Use option setting.

bfd/
	* elflink.c (bfd_elf_define_start_stop): Use start_stop_visibility
	field of bfd_link_info.

include/
	* bfdlink.h (struct bfd_link_info): New field start_stop_visibility.

ld/
	* NEWS: Mention -z start-stop-visibility=... option for ELF.
	* ld.texi (Options): Document -z start-stop-visibility=... option.
	* ldmain.c (main): Initialize link_info.start_stop_visibility.
	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option):
	Parse -z start-stop-visibility=... option.

4 files changed, 45 insertions, 3 deletions

diff --git a/gold/ChangeLog b/gold/ChangeLog
index f3d3715..1f9c523 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,3 +1,15 @@
+2020-06-15  Roland McGrath  <mcgrathr@google.com>
+
+	Implement -z start-stop-visibility=... option.
+	* options.h (class General_options): Handle -z start-stop-visibility=.
+	(General_options::start_stop_visibility_enum): New public method.
+	(General_options::set_start_stop_visibility_enum): New private method.
+	(General_options::start_stop_visibility_enum_): New private member.
+	* options.cc (General_options::General_options): Add initializer.
+	(General_options::finalize): Set this->start_stop_visibility_enum_
+	from string value.
+	* layout.cc (Layout::define_section_symbols): Use option setting.
+
 2020-06-06  Alan Modra  <amodra@gmail.com>
 
 	* powerpc.cc: Update throughout for reloc renaming.
diff --git a/gold/layout.cc b/gold/layout.cc
index be437f3..b3b0c57 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -2474,6 +2474,7 @@ Layout::create_initial_dynamic_sections(Symbol_table* symtab)
 void
 Layout::define_section_symbols(Symbol_table* symtab)
 {
+  const elfcpp::STV visibility = parameters->options().start_stop_visibility_enum();
   for (Section_list::const_iterator p = this->section_list_.begin();
        p != this->section_list_.end();
        ++p)
@@ -2495,7 +2496,7 @@ Layout::define_section_symbols(Symbol_table* symtab)
 					0, // symsize
 					elfcpp::STT_NOTYPE,
 					elfcpp::STB_GLOBAL,
-					elfcpp::STV_PROTECTED,
+					visibility,
 					0, // nonvis
 					false, // offset_is_from_end
 					true); // only_if_ref
@@ -2508,7 +2509,7 @@ Layout::define_section_symbols(Symbol_table* symtab)
 					0, // symsize
 					elfcpp::STT_NOTYPE,
 					elfcpp::STB_GLOBAL,
-					elfcpp::STV_PROTECTED,
+					visibility,
 					0, // nonvis
 					true, // offset_is_from_end
 					true); // only_if_ref
diff --git a/gold/options.cc b/gold/options.cc
index 94867b3..b13ae71 100644
--- a/gold/options.cc
+++ b/gold/options.cc
@@ -997,7 +997,8 @@ General_options::General_options()
     fix_v4bx_(FIX_V4BX_NONE),
     endianness_(ENDIANNESS_NOT_SET),
     discard_locals_(DISCARD_SEC_MERGE),
-    orphan_handling_enum_(ORPHAN_PLACE)
+    orphan_handling_enum_(ORPHAN_PLACE),
+    start_stop_visibility_enum_(elfcpp::STV_PROTECTED)
 {
   // Turn off option registration once construction is complete.
   gold::options::ready_to_register = false;
@@ -1169,6 +1170,19 @@ General_options::finalize()
         this->set_orphan_handling_enum(ORPHAN_ERROR);
     }
 
+  // Parse the -z start-stop-visibility argument.
+  if (this->user_set_start_stop_visibility())
+    {
+      if (strcmp(this->start_stop_visibility(), "default") == 0)
+        this->set_start_stop_visibility_enum(elfcpp::STV_DEFAULT);
+      else if (strcmp(this->start_stop_visibility(), "internal") == 0)
+        this->set_start_stop_visibility_enum(elfcpp::STV_INTERNAL);
+      else if (strcmp(this->start_stop_visibility(), "hidden") == 0)
+        this->set_start_stop_visibility_enum(elfcpp::STV_HIDDEN);
+      else if (strcmp(this->start_stop_visibility(), "protected") == 0)
+        this->set_start_stop_visibility_enum(elfcpp::STV_PROTECTED);
+    }
+
   // -M is equivalent to "-Map -".
   if (this->print_map() && !this->user_set_Map())
     {
diff --git a/gold/options.h b/gold/options.h
index b2059d9..f0e9fbd 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1500,6 +1500,11 @@ class General_options
 	      N_("Don't mark variables read-only after relocation"));
   DEFINE_uint64(stack_size, options::DASH_Z, '\0', 0,
 		N_("Set PT_GNU_STACK segment p_memsz to SIZE"), N_("SIZE"));
+  DEFINE_enum(start_stop_visibility, options::DASH_Z, '\0', "protected",
+              N_("ELF symbol visibility for synthesized "
+                 "__start_* and __stop_* symbols"),
+              ("[default,internal,hidden,protected]"),
+              {"default", "internal", "hidden", "protected"});
   DEFINE_bool(text, options::DASH_Z, '\0', false,
 	      N_("Do not permit relocations in read-only segments"),
 	      N_("Permit relocations in read-only segments"));
@@ -1750,6 +1755,10 @@ class General_options
   orphan_handling_enum() const
   { return this->orphan_handling_enum_; }
 
+  elfcpp::STV
+  start_stop_visibility_enum() const
+  { return this->start_stop_visibility_enum_; }
+
  private:
   // Don't copy this structure.
   General_options(const General_options&);
@@ -1809,6 +1818,10 @@ class General_options
   set_orphan_handling_enum(Orphan_handling value)
   { this->orphan_handling_enum_ = value; }
 
+  void
+  set_start_stop_visibility_enum(elfcpp::STV value)
+  { this->start_stop_visibility_enum_ = value; }
+
   // These are called by finalize() to set up the search-path correctly.
   void
   add_to_library_path_with_sysroot(const std::string& arg)
@@ -1876,6 +1889,8 @@ class General_options
   std::vector<Position_dependent_options*> options_stack_;
   // Orphan handling option, decoded to an enum value.
   Orphan_handling orphan_handling_enum_;
+  // Symbol visibility for __start_* / __stop_* magic symbols.
+  elfcpp::STV start_stop_visibility_enum_;
 };
 
 // The position-dependent options.  We use this to store the state of