Patch adds support to allow plugins to map selected subset of sections to unique

segments.


2012-08-24  Sriraman Tallam  <tmsriram@google.com>

	* gold.cc (queue_middle_tasks): Call layout again when unique
	segments for sections is desired.
	* layout.cc (Layout::Layout): Initialize new members.
	(Layout::get_output_section_flags): New function.
	(Layout::choose_output_section): Call get_output_section_flags.
	(Layout::layout): Make output section for mapping to a unique segment.
	(Layout::insert_section_segment_map): New function.
	(Layout::attach_allocated_section_to_segment): Make unique segment for
	output sections marked so.
	(Layout::segment_precedes): Check for unique segments when sorting.
	* layout.h (Layout::Unique_segment_info): New struct.
	(Layout::Section_segment_map): New typedef.
	(Layout::insert_section_segment_map): New function.
	(Layout::get_output_section_flags): New function.
	(Layout::is_unique_segment_for_sections_specified): New function.
	(Layout::set_unique_segment_for_sections_specified): New function.
	(Layout::unique_segment_for_sections_specified_): New member.
	(Layout::section_segment_map_): New member.
	* object.cc (Sized_relobj_file<size, big_endian>::do_layout):
	Rename is_gc_pass_one to is_pass_one.
	Rename is_gc_pass_two to is_pass_two.
	Rename is_gc_or_icf to is_two_pass.
	Check for which pass based on whether symbols data is present.
	Make it two pass when unique segments for sections is desired.
	* output.cc (Output_section::Output_section): Initialize new
	members.
	* output.h (Output_section::is_unique_segment): New function.
	(Output_section::set_is_unique_segment): New function.
	(Output_section::is_unique_segment_): New member.
	(Output_section::extra_segment_flags): New function.
	(Output_section::set_extra_segment_flags): New function.
	(Output_section::extra_segment_flags_): New member.
	(Output_section::segment_alignment): New function.
	(Output_section::set_segment_alignment): New function.
	(Output_section::segment_alignment_): New member.
	(Output_segment::Output_segment): Initialize is_unique_segment_.
	(Output_segment::is_unique_segment): New function.
	(Output_segment::set_is_unique_segment): New function.
	(Output_segment::is_unique_segment_): New member.
	* plugin.cc (allow_unique_segment_for_sections): New function.
	(unique_segment_for_sections): New function.
	(Plugin::load): Add new functions to transfer vector.
	* Makefile.am (plugin_final_layout.readelf.stdout): Add readelf output.
	* Makefile.in: Regenerate.
	* testsuite/plugin_final_layout.sh: Check if unique segment
	functionality works.
	* testsuite/plugin_section_order.c (onload): Check if new interfaces
	are available.
	(allow_unique_segment_for_sections): New global.
	(unique_segment_for_sections): New global.
	(claim_file_hook): Call allow_unique_segment_for_sections.
	(all_symbols_read_hook): Call unique_segment_for_sections.


2012-08-24  Sriraman Tallam  <tmsriram@google.com>

	* plugin-api.h (ld_plugin_allow_unique_segment_for_sections):
	New interface.
	(ld_plugin_unique_segment_for_sections): New interface.
	(LDPT_ALLOW_UNIQUE_SEGMENT_FOR_SECTIONS): New enum val.
	(LDPT_UNIQUE_SEGMENT_FOR_SECTIONS): New enum val.
	(tv_allow_unique_segment_for_sections): New member.
	(tv_unique_segment_for_sections): New member.

1 files changed, 123 insertions, 53 deletions

diff --git a/gold/layout.cc b/gold/layout.cc
index db6b6ac..cadac87 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -408,12 +408,14 @@ Layout::Layout(int number_of_input_files, Script_options* script_options)
     resized_signatures_(false),
     have_stabstr_section_(false),
     section_ordering_specified_(false),
+    unique_segment_for_sections_specified_(false),
     incremental_inputs_(NULL),
     record_output_section_data_from_script_(false),
     script_output_section_data_list_(),
     segment_states_(NULL),
     relaxation_debug_check_(NULL),
     section_order_map_(),
+    section_segment_map_(),
     input_section_position_(),
     input_section_glob_(),
     incremental_base_(NULL),
@@ -824,6 +826,27 @@ Layout::keep_input_section(const Relobj* relobj, const char* name)
   return name != NULL && keep;
 }
 
+// Clear the input section flags that should not be copied to the
+// output section.
+
+elfcpp::Elf_Xword
+Layout::get_output_section_flags(elfcpp::Elf_Xword input_section_flags)
+{
+  // Some flags in the input section should not be automatically
+  // copied to the output section.
+  input_section_flags &= ~ (elfcpp::SHF_INFO_LINK
+			    | elfcpp::SHF_GROUP
+			    | elfcpp::SHF_MERGE
+			    | elfcpp::SHF_STRINGS);
+
+  // We only clear the SHF_LINK_ORDER flag in for
+  // a non-relocatable link.
+  if (!parameters->options().relocatable())
+    input_section_flags &= ~elfcpp::SHF_LINK_ORDER;
+
+  return input_section_flags;
+}
+
 // Pick the output section to use for section NAME, in input file
 // RELOBJ, with type TYPE and flags FLAGS.  RELOBJ may be NULL for a
 // linker created section.  IS_INPUT_SECTION is true if we are
@@ -842,17 +865,7 @@ Layout::choose_output_section(const Relobj* relobj, const char* name,
   // sections to segments.
   gold_assert(!is_input_section || !this->sections_are_attached_);
 
-  // Some flags in the input section should not be automatically
-  // copied to the output section.
-  flags &= ~ (elfcpp::SHF_INFO_LINK
-	      | elfcpp::SHF_GROUP
-	      | elfcpp::SHF_MERGE
-	      | elfcpp::SHF_STRINGS);
-
-  // We only clear the SHF_LINK_ORDER flag in for
-  // a non-relocatable link.
-  if (!parameters->options().relocatable())
-    flags &= ~elfcpp::SHF_LINK_ORDER;
+  flags = this->get_output_section_flags(flags);
 
   if (this->script_options_->saw_sections_clause())
     {
@@ -1054,9 +1067,37 @@ Layout::layout(Sized_relobj_file<size, big_endian>* object, unsigned int shndx,
     }
   else
     {
-      os = this->choose_output_section(object, name, sh_type,
-				       shdr.get_sh_flags(), true,
-				       ORDER_INVALID, false);
+      // Plugins can choose to place one or more subsets of sections in
+      // unique segments and this is done by mapping these section subsets
+      // to unique output sections.  Check if this section needs to be
+      // remapped to a unique output section.
+      Section_segment_map::iterator it
+	  = this->section_segment_map_.find(Const_section_id(object, shndx));
+      if (it == this->section_segment_map_.end())
+	{
+          os = this->choose_output_section(object, name, sh_type,
+					   shdr.get_sh_flags(), true,
+					   ORDER_INVALID, false);
+	}
+      else
+	{
+	  // We know the name of the output section, directly call
+	  // get_output_section here by-passing choose_output_section.
+	  elfcpp::Elf_Xword flags
+	    = this->get_output_section_flags(shdr.get_sh_flags());
+
+	  const char* os_name = it->second->name;
+	  Stringpool::Key name_key;
+	  os_name = this->namepool_.add(os_name, true, &name_key);
+	  os = this->get_output_section(os_name, name_key, sh_type, flags,
+					ORDER_INVALID, false);
+	  if (!os->is_unique_segment())
+	    {
+	      os->set_is_unique_segment();
+	      os->set_extra_segment_flags(it->second->flags);
+	      os->set_segment_alignment(it->second->align);
+	    }
+	}
       if (os == NULL)
 	return NULL;
     }
@@ -1116,6 +1157,15 @@ Layout::layout(Sized_relobj_file<size, big_endian>* object, unsigned int shndx,
   return os;
 }
 
+// Maps section SECN to SEGMENT s.
+void
+Layout::insert_section_segment_map(Const_section_id secn,
+				   Unique_segment_info *s)
+{
+  gold_assert(this->unique_segment_for_sections_specified_); 
+  this->section_segment_map_[secn] = s;
+}
+
 // Handle a relocation section when doing a relocatable link.
 
 template<int size, bool big_endian>
@@ -1718,6 +1768,10 @@ Layout::attach_allocated_section_to_segment(const Target* target,
 
   elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags);
 
+  // If this output section's segment has extra flags that need to be set,
+  // coming from a linker plugin, do that.
+  seg_flags |= os->extra_segment_flags();
+
   // Check for --section-start.
   uint64_t addr;
   bool is_address_set = parameters->options().section_start(os->name(), &addr);
@@ -1730,45 +1784,51 @@ Layout::attach_allocated_section_to_segment(const Target* target,
   // have to use a linker script.
 
   Segment_list::const_iterator p;
-  for (p = this->segment_list_.begin();
-       p != this->segment_list_.end();
-       ++p)
+  if (!os->is_unique_segment())
     {
-      if ((*p)->type() != elfcpp::PT_LOAD)
-	continue;
-      if (!parameters->options().omagic()
-	  && ((*p)->flags() & elfcpp::PF_W) != (seg_flags & elfcpp::PF_W))
-	continue;
-      if ((target->isolate_execinstr() || parameters->options().rosegment())
-	  && ((*p)->flags() & elfcpp::PF_X) != (seg_flags & elfcpp::PF_X))
-	continue;
-      // If -Tbss was specified, we need to separate the data and BSS
-      // segments.
-      if (parameters->options().user_set_Tbss())
-	{
-	  if ((os->type() == elfcpp::SHT_NOBITS)
-	      == (*p)->has_any_data_sections())
-	    continue;
-	}
-      if (os->is_large_data_section() && !(*p)->is_large_data_segment())
-	continue;
-
-      if (is_address_set)
+      for (p = this->segment_list_.begin();
+ 	   p != this->segment_list_.end();
+	   ++p)
 	{
-	  if ((*p)->are_addresses_set())
-	    continue;
-
-	  (*p)->add_initial_output_data(os);
-	  (*p)->update_flags_for_output_section(seg_flags);
-	  (*p)->set_addresses(addr, addr);
-	  break;
-	}
-
-      (*p)->add_output_section_to_load(this, os, seg_flags);
-      break;
-    }
-
-  if (p == this->segment_list_.end())
+	  if ((*p)->type() != elfcpp::PT_LOAD)                        
+	    continue;                        
+	  if ((*p)->is_unique_segment())                        
+	    continue;                        
+	  if (!parameters->options().omagic()                        
+	      && ((*p)->flags() & elfcpp::PF_W) != (seg_flags & elfcpp::PF_W))                        
+	    continue;                        
+	  if ((target->isolate_execinstr() || parameters->options().rosegment())                        
+	      && ((*p)->flags() & elfcpp::PF_X) != (seg_flags & elfcpp::PF_X))                        
+	    continue;                        
+	  // If -Tbss was specified, we need to separate the data and BSS                        
+	  // segments.                        
+	  if (parameters->options().user_set_Tbss())                        
+	    {                        
+	      if ((os->type() == elfcpp::SHT_NOBITS)                        
+	          == (*p)->has_any_data_sections())                        
+	        continue;                        
+	    }                        
+	  if (os->is_large_data_section() && !(*p)->is_large_data_segment())                        
+	    continue;                        
+	                    
+	  if (is_address_set)                        
+	    {                        
+	      if ((*p)->are_addresses_set())                        
+	        continue;                        
+	                    
+	      (*p)->add_initial_output_data(os);                        
+	      (*p)->update_flags_for_output_section(seg_flags);                        
+	      (*p)->set_addresses(addr, addr);                        
+	      break;                        
+	    }                        
+	                    
+	  (*p)->add_output_section_to_load(this, os, seg_flags);                        
+	  break;                        
+	}                        
+    }
+
+  if (p == this->segment_list_.end()
+      || os->is_unique_segment())
     {
       Output_segment* oseg = this->make_output_segment(elfcpp::PT_LOAD,
 						       seg_flags);
@@ -1777,6 +1837,14 @@ Layout::attach_allocated_section_to_segment(const Target* target,
       oseg->add_output_section_to_load(this, os, seg_flags);
       if (is_address_set)
 	oseg->set_addresses(addr, addr);
+      // Check if segment should be marked unique.  For segments marked
+      // unique by linker plugins, set the new alignment if specified.
+      if (os->is_unique_segment())
+	{
+	  oseg->set_is_unique_segment();
+	  if (os->segment_alignment() != 0)
+	    oseg->set_minimum_p_align(os->segment_alignment());
+	}
     }
 
   // If we see a loadable SHT_NOTE section, we create a PT_NOTE
@@ -3121,9 +3189,11 @@ Layout::segment_precedes(const Output_segment* seg1,
 
   // We shouldn't get here--we shouldn't create segments which we
   // can't distinguish.  Unless of course we are using a weird linker
-  // script or overlapping --section-start options.
+  // script or overlapping --section-start options.  We could also get
+  // here if plugins want unique segments for subsets of sections.
   gold_assert(this->script_options_->saw_phdrs_clause()
-	      || parameters->options().any_section_start());
+	      || parameters->options().any_section_start()
+	      || this->is_unique_segment_for_sections_specified());
   return false;
 }