[gold] Implement -z stack-size option

gold/
	* options.h (General_options): Grok -z stack-size.
	* output.h (Output_segment::set_size): New method.
	* layout.cc (Layout::create_executable_stack_info): Renamed to ...
	(Layout::create_stack_segment): ... this.  Always create the
	segment if -z stack-size was used.
	(Layout::set_segment_offsets): Don't call ->set_offset on the
	PT_GNU_STACK segment.

gold/ChangeLog

@@ -1,3 +1,13 @@
+2016-08-23  Roland McGrath  <roland@hack.frob.com>
+
+	* options.h (General_options): Grok -z stack-size.
+	* output.h (Output_segment::set_size): New method.
+	* layout.cc (Layout::create_executable_stack_info): Renamed to ...
+	(Layout::create_stack_segment): ... this.  Always create the
+	segment if -z stack-size was used.
+	(Layout::set_segment_offsets): Don't call ->set_offset on the
+	PT_GNU_STACK segment.
+
 2016-08-15  Bharathi Seshadri  <bseshadr@cisco.com>
 
 	* options.h (General_options): Add --be8 option.

gold/layout.cc

@@ -2135,7 +2135,7 @@ void
 Layout::create_notes()
 {
   this->create_gold_note();
-  this->create_executable_stack_info();
+  this->create_stack_segment();
   this->create_build_id();
 }
 
@@ -2985,13 +2985,15 @@ Layout::create_gold_note()
 // executable.  Otherwise, if at least one input file a
 // .note.GNU-stack section, and some input file has no .note.GNU-stack
 // section, we use the target default for whether the stack should be
-// executable.  Otherwise, we don't generate a stack note.  When
+// executable.  If -z stack-size was used to set a p_memsz value for
-// generating a object file, we create a .note.GNU-stack section with
+// PT_GNU_STACK, we generate the segment regardless.  Otherwise, we
-// the appropriate marking.  When generating an executable or shared
+// don't generate a stack note.  When generating a object file, we
-// library, we create a PT_GNU_STACK segment.
+// create a .note.GNU-stack section with the appropriate marking.
+// When generating an executable or shared library, we create a
+// PT_GNU_STACK segment.
 
 void
-Layout::create_executable_stack_info()
+Layout::create_stack_segment()
 {
   bool is_stack_executable;
   if (parameters->options().is_execstack_set())
@@ -3003,7 +3005,9 @@ Layout::create_executable_stack_info()
 	gold_warning(_("one or more inputs require executable stack, "
 		       "but -z noexecstack was given"));
     }
-  else if (!this->input_with_gnu_stack_note_)
+  else if (!this->input_with_gnu_stack_note_
+	   && (!parameters->options().user_set_stack_size()
+	       || parameters->options().relocatable()))
     return;
   else
     {
@@ -3032,7 +3036,12 @@ Layout::create_executable_stack_info()
       int flags = elfcpp::PF_R | elfcpp::PF_W;
       if (is_stack_executable)
 	flags |= elfcpp::PF_X;
+      Output_segment* seg =
 	this->make_output_segment(elfcpp::PT_GNU_STACK, flags);
+      seg->set_size(parameters->options().stack_size());
+      // BFD lets targets override this default alignment, but the only
+      // targets that do so are ones that Gold does not support so far.
+      seg->set_minimum_p_align(16);
     }
 }
 
@@ -3718,7 +3727,9 @@ Layout::set_segment_offsets(const Target* target, Output_segment* load_seg,
        p != this->segment_list_.end();
        ++p)
     {
-      if ((*p)->type() != elfcpp::PT_LOAD)
+      // PT_GNU_STACK was set up correctly when it was created.
+      if ((*p)->type() != elfcpp::PT_LOAD
+	  && (*p)->type() != elfcpp::PT_GNU_STACK)
 	(*p)->set_offset((*p)->type() == elfcpp::PT_GNU_RELRO
 			 ? increase_relro
 			 : 0);

gold/layout.h

@@ -1037,9 +1037,9 @@ class Layout
   void
   create_gold_note();
 
-  // Record whether the stack must be executable.
+  // Record whether the stack must be executable, and a user-supplied size.
   void
-  create_executable_stack_info();
+  create_stack_segment();
 
   // Create a build ID note if needed.
   void

gold/options.h

@@ -1342,6 +1342,8 @@ class General_options
   DEFINE_bool(relro, options::DASH_Z, '\0', DEFAULT_LD_Z_RELRO,
 	      N_("Where possible mark variables read-only after relocation"),
 	      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_bool(text, options::DASH_Z, '\0', false,
 	      N_("Do not permit relocations in read-only segments"),
 	      N_("Permit relocations in read-only segments (default)"));

gold/output.h

@@ -4796,6 +4796,13 @@ class Output_segment
       this->min_p_align_ = align;
   }
 
+  // Set the memory size of this segment.
+  void
+  set_size(uint64_t size)
+  {
+    this->memsz_ = size;
+  }
+
   // Set the offset of this segment based on the section.  This should
   // only be called for a non-PT_LOAD segment.
   void