[PATCH][gold] Add support for DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL.

[Vladimir Radosavljevic <Vladimir dot Radosavljevic at imgtec dot com>]

This patch adds support for DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL dynamic tags,
.rld_map section, and __RLD_MAP symbol.

Regards,
Vladimir

ChangeLog -

elfcpp/
	* elfcpp.h (DT_MIPS_RLD_MAP_REL): New enum constant.
gold/
	* mips.cc (Target_mips::Target_mips): Initialize rld_map_.
	(Target_mips::rld_map_): New data member.
	(Target_mips::do_finalize_sections): Add support for
	DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL dynamic tags,
	.rld_map section, and __RLD_MAP symbol.
	(Target_mips::do_dynamic_tag_custom_value): Add support for
	DT_MIPS_RLD_MAP_REL dynamic tag.
	* output.cc (Output_data_dynamic::get_entry_offset): New method
	definition.
	* output.h (Output_data_dynamic::get_entry_offset): New method
	declaration.

diff --git a/elfcpp/elfcpp.h b/elfcpp/elfcpp.h
index f39a135..7469bd8 100644
--- a/elfcpp/elfcpp.h
+++ b/elfcpp/elfcpp.h
@@ -868,6 +868,8 @@ enum DT
   DT_MIPS_PLTGOT = 0x70000032,
   // Points to the base of a writable PLT.
   DT_MIPS_RWPLT = 0x70000034,
+  // Relative offset of run time loader map, used for debugging.
+  DT_MIPS_RLD_MAP_REL = 0x70000035,
 
   DT_AUXILIARY = 0x7ffffffd,
   DT_USED = 0x7ffffffe,
diff --git a/gold/mips.cc b/gold/mips.cc
index e2b7855..3cc5989 100644
--- a/gold/mips.cc
+++ b/gold/mips.cc
@@ -3292,7 +3292,7 @@ class Target_mips : public Sized_target<size, big_endian>
  public:
   Target_mips(const Target::Target_info* info = &mips_info)
     : Sized_target<size, big_endian>(info), got_(NULL), gp_(NULL), plt_(NULL),
-      got_plt_(NULL), rel_dyn_(NULL), copy_relocs_(), dyn_relocs_(),
+      got_plt_(NULL), rel_dyn_(NULL), rld_map_(NULL), copy_relocs_(), dyn_relocs_(),
       la25_stub_(NULL), mips_mach_extensions_(), mips_stubs_(NULL),
       attributes_section_data_(NULL), abiflags_(NULL), mach_(0), layout_(NULL),
       got16_addends_(), has_abiflags_section_(false),
@@ -4181,6 +4181,8 @@ class Target_mips : public Sized_target<size, big_endian>
   Output_data_space* got_plt_;
   // The dynamic reloc section.
   Reloc_section* rel_dyn_;
+  // The .rld_map section.
+  Output_data_zero_fill* rld_map_;
   // Relocs saved to avoid a COPY reloc.
   Mips_copy_relocs<elfcpp::SHT_REL, size, big_endian> copy_relocs_;
 
@@ -9760,8 +9762,37 @@ Target_mips<size, big_endian>::do_finalize_sections(Layout* layout,
     if (this->plt_ != NULL)
       // DT_MIPS_PLTGOT dynamic tag
       odyn->add_section_address(elfcpp::DT_MIPS_PLTGOT, this->got_plt_);
+
+    if (!parameters->options().shared())
+      {
+        this->rld_map_ = new Output_data_zero_fill(size / 8, size / 8);
+
+        layout->add_output_section_data(".rld_map", elfcpp::SHT_PROGBITS,
+                                        (elfcpp::SHF_ALLOC | elfcpp::SHF_WRITE),
+                                        this->rld_map_, ORDER_INVALID, false);
+
+        // __RLD_MAP will be filled in by the runtime loader to contain
+        // a pointer to the _r_debug structure.
+        Symbol* rld_map = symtab->define_in_output_data("__RLD_MAP", NULL,
+                                            Symbol_table::PREDEFINED,
+                                            this->rld_map_,
+                                            0, 0, elfcpp::STT_OBJECT,
+                                            elfcpp::STB_GLOBAL,
+                                            elfcpp::STV_DEFAULT, 0,
+                                            false, false);
+
+        rld_map->set_needs_dynsym_entry();
+
+        if (!parameters->options().pie())
+          // This member holds the absolute address of the debug pointer.
+          odyn->add_section_address(elfcpp::DT_MIPS_RLD_MAP, this->rld_map_);
+        else
+          // This member holds the offset to the debug pointer,
+          // relative to the address of the tag.
+          odyn->add_custom(elfcpp::DT_MIPS_RLD_MAP_REL);
+      }
   }
- }
+}
 
 // Get the custom dynamic tag value.
 template<int size, bool big_endian>
@@ -9797,6 +9828,16 @@ Target_mips<size, big_endian>::do_dynamic_tag_custom_value(elfcpp::DT tag) const
           return this->get_dt_mips_symtabno();
       }
 
+    case elfcpp::DT_MIPS_RLD_MAP_REL:
+      {
+        // The MIPS_RLD_MAP_REL tag stores the offset to the debug pointer,
+        // relative to the address of the tag.
+        Output_data_dynamic* const odyn = this->layout_->dynamic_data();
+        unsigned int entry_offset =
+          odyn->get_entry_offset(elfcpp::DT_MIPS_RLD_MAP_REL);
+        gold_assert(entry_offset != -1U);
+        return this->rld_map_->address() - (odyn->address() + entry_offset);
+      }
     default:
       gold_error(_("Unknown dynamic tag 0x%x"), (unsigned int)tag);
     }
diff --git a/gold/output.cc b/gold/output.cc
index 077e2c4..26291c6 100644
--- a/gold/output.cc
+++ b/gold/output.cc
@@ -1882,6 +1882,26 @@ Output_data_dynamic::do_adjust_output_section(Output_section* os)
     gold_unreachable();
 }
 
+// Get a dynamic entry offset.
+
+unsigned int
+Output_data_dynamic::get_entry_offset(elfcpp::DT tag) const
+{
+  int dyn_size;
+  if (parameters->target().get_size() == 32)
+    dyn_size = elfcpp::Elf_sizes<32>::dyn_size;
+  else if (parameters->target().get_size() == 64)
+    dyn_size = elfcpp::Elf_sizes<64>::dyn_size;
+  else
+    gold_unreachable();
+
+  for (size_t i = 0; i < entries_.size(); ++i)
+    if (entries_[i].tag() == tag)
+      return i * dyn_size;
+
+  return -1U;
+}
+
 // Set the final data size.
 
 void
diff --git a/gold/output.h b/gold/output.h
index 0b96a03..d8a8aaa 100644
--- a/gold/output.h
+++ b/gold/output.h
@@ -2781,6 +2781,10 @@ class Output_data_dynamic : public Output_section_data
   add_custom(elfcpp::DT tag)
   { this->add_entry(Dynamic_entry(tag)); }
 
+  // Get a dynamic entry offset.
+  unsigned int
+  get_entry_offset(elfcpp::DT tag) const;
+
  protected:
   // Adjust the output section to set the entry size.
   void