gold patch committed: Initialize first .got.plt entry

[Ian Lance Taylor <iant at google dot com>]

I somehow managed to overlook the x86/x86_64 ELF ABI requirement that
the first entry in the .got.plt section hold the unrelocated address of
the .dynamic section.  I got away with it because the only program which
cares is the dynamic linker itself.  This patch fixes the problem.
Committed to mainline.

Ian


2011-07-15  Ian Lance Taylor  <iant@google.com>

	* i386.cc (class Output_data_plt_i386): Add layout_ field.
	(Output_data_plt_i386::Output_data_plt_i386): Initialize layout_.
	(Output_data_plt_i386::do_write): Write address of .dynamic
	section to first entry in .got.plt section.
	* x86_64.cc (class Output_data_plt_x86_64): Add layout_ field.
	(Output_data_plt_x86_64::Output_data_plt_x86_64) [both versions]:
	Initialize layout_.
	(Output_data_plt_x86_64::do_write): Write address of .dynamic
	section to first entry in .got.plt section.
	* layout.h (Layout::dynamic_section): New function.


Index: i386.cc
===================================================================
RCS file: /cvs/src/src/gold/i386.cc,v
retrieving revision 1.140
diff -u -p -r1.140 i386.cc
--- i386.cc	13 Jul 2011 22:47:07 -0000	1.140
+++ i386.cc	15 Jul 2011 15:16:43 -0000
@@ -166,6 +166,9 @@ class Output_data_plt_i386 : public Outp
     unsigned int got_offset;
   };
 
+  // A pointer to the Layout class, so that we can find the .dynamic
+  // section when we write out the GOT PLT section.
+  Layout* layout_;
   // The reloc section.
   Reloc_section* rel_;
   // The TLS_DESC relocations, if necessary.  These must follow the
@@ -822,9 +825,9 @@ Target_i386::rel_irelative_section(Layou
 Output_data_plt_i386::Output_data_plt_i386(Layout* layout,
 					   Output_data_space* got_plt,
 					   Output_data_space* got_irelative)
-  : Output_section_data(16), tls_desc_rel_(NULL), irelative_rel_(NULL),
-    got_plt_(got_plt), got_irelative_(got_irelative), count_(0),
-    irelative_count_(0), global_ifuncs_(), local_ifuncs_()
+  : Output_section_data(16), layout_(layout), tls_desc_rel_(NULL),
+    irelative_rel_(NULL), got_plt_(got_plt), got_irelative_(got_irelative),
+    count_(0), irelative_count_(0), global_ifuncs_(), local_ifuncs_()
 {
   this->rel_ = new Reloc_section(false);
   layout->add_output_section_data(".rel.plt", elfcpp::SHT_REL,
@@ -1138,8 +1141,16 @@ Output_data_plt_i386::do_write(Output_fi
 
   unsigned char* got_pov = got_view;
 
-  memset(got_pov, 0, 12);
-  got_pov += 12;
+  // The first entry in the GOT is the address of the .dynamic section
+  // aka the PT_DYNAMIC segment.  The next two entries are reserved.
+  // We saved space for them when we created the section in
+  // Target_i386::got_section.
+  Output_section* dynamic = this->layout_->dynamic_section();
+  uint32_t dynamic_addr = dynamic == NULL ? 0 : dynamic->address();
+  elfcpp::Swap<32, false>::writeval(got_pov, dynamic_addr);
+  got_pov += 4;
+  memset(got_pov, 0, 8);
+  got_pov += 8;
 
   const int rel_size = elfcpp::Elf_sizes<32>::rel_size;
 
Index: layout.h
===================================================================
RCS file: /cvs/src/src/gold/layout.h,v
retrieving revision 1.98
diff -u -p -r1.98 layout.h
--- layout.h	14 Jul 2011 00:55:17 -0000	1.98
+++ layout.h	15 Jul 2011 15:16:43 -0000
@@ -627,6 +627,12 @@ class Layout
   dynpool() const
   { return &this->dynpool_; }
 
+  // Return the .dynamic output section.  This is only valid after the
+  // layout has been finalized.
+  Output_section*
+  dynamic_section() const
+  { return this->dynamic_section_; }
+
   // Return the symtab_xindex section used to hold large section
   // indexes for the normal symbol table.
   Output_symtab_xindex*
Index: x86_64.cc
===================================================================
RCS file: /cvs/src/src/gold/x86_64.cc,v
retrieving revision 1.138
diff -u -p -r1.138 x86_64.cc
--- x86_64.cc	13 Jul 2011 22:47:07 -0000	1.138
+++ x86_64.cc	15 Jul 2011 15:16:43 -0000
@@ -57,9 +57,10 @@ class Output_data_plt_x86_64 : public Ou
   Output_data_plt_x86_64(Layout* layout, Output_data_got<64, false>* got,
 			 Output_data_space* got_plt,
 			 Output_data_space* got_irelative)
-    : Output_section_data(16), tlsdesc_rel_(NULL), irelative_rel_(NULL),
-      got_(got), got_plt_(got_plt), got_irelative_(got_irelative), count_(0),
-      irelative_count_(0), tlsdesc_got_offset_(-1U), free_list_()
+    : Output_section_data(16), layout_(layout), tlsdesc_rel_(NULL),
+      irelative_rel_(NULL), got_(got), got_plt_(got_plt),
+      got_irelative_(got_irelative), count_(0), irelative_count_(0),
+      tlsdesc_got_offset_(-1U), free_list_()
   { this->init(layout); }
 
   Output_data_plt_x86_64(Layout* layout, Output_data_got<64, false>* got,
@@ -67,9 +68,9 @@ class Output_data_plt_x86_64 : public Ou
 			 Output_data_space* got_irelative,
 			 unsigned int plt_count)
     : Output_section_data((plt_count + 1) * plt_entry_size, 16, false),
-      tlsdesc_rel_(NULL), irelative_rel_(NULL), got_(got), got_plt_(got_plt),
-      got_irelative_(got_irelative), count_(plt_count), irelative_count_(0),
-      tlsdesc_got_offset_(-1U), free_list_()
+      layout_(layout), tlsdesc_rel_(NULL), irelative_rel_(NULL), got_(got),
+      got_plt_(got_plt), got_irelative_(got_irelative), count_(plt_count),
+      irelative_count_(0), tlsdesc_got_offset_(-1U), free_list_()
   {
     this->init(layout);
 
@@ -205,6 +206,9 @@ class Output_data_plt_x86_64 : public Ou
   void
   do_write(Output_file*);
 
+  // A pointer to the Layout class, so that we can find the .dynamic
+  // section when we write out the GOT PLT section.
+  Layout* layout_;
   // The reloc section.
   Reloc_section* rel_;
   // The TLSDESC relocs, if necessary.  These must follow the regular
@@ -1306,8 +1310,16 @@ Output_data_plt_x86_64::do_write(Output_
 
   unsigned char* got_pov = got_view;
 
-  memset(got_pov, 0, 24);
-  got_pov += 24;
+  // The first entry in the GOT is the address of the .dynamic section
+  // aka the PT_DYNAMIC segment.  The next two entries are reserved.
+  // We saved space for them when we created the section in
+  // Target_i386::got_section.
+  Output_section* dynamic = this->layout_->dynamic_section();
+  uint32_t dynamic_addr = dynamic == NULL ? 0 : dynamic->address();
+  elfcpp::Swap<64, false>::writeval(got_pov, dynamic_addr);
+  got_pov += 8;
+  memset(got_pov, 0, 16);
+  got_pov += 16;
 
   unsigned int plt_offset = plt_entry_size;
   unsigned int got_offset = 24;