[GOLD] powerpc _SDA_BASE_ segfault

[Alan Modra <amodra at gmail dot com>]

This avoids a gold segfault found when linking the linux kernel
vdso32, by only creating _SDA_BASE_ when the symbol is referenced.
Not a proper fix, because someone could hit the same segfault if sda
relocs were used (not supported yet by gold) with a link script that
/DISCARD/s .sdata as the kernel vdso script does.

I also move setting up _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ to
do_scan_relocs, which is called once, rather that once per section in
scan_relocs (or even worse, once per reloc as done by some other
target code).

	* powerpc.cc (Powerpc_relobj): Delete "Offset" typedef.
	(struct Opd_ent): Use "Address" rather than "Offset".
	(Output_data_got_powerpc::got_base_offset): Return Valtype.
	(Target_powerpc::got_section): Make public.
	(Target_powerpc::scan_relocs): Move code setting symbols..
	(Powerpc_relobj::do_scan_relocs): ..to here, new function.
	Create _SDA_BASE_ only when referenced.

Index: gold/powerpc.cc
===================================================================
RCS file: /cvs/src/src/gold/powerpc.cc,v
retrieving revision 1.67
diff -u -p -r1.67 powerpc.cc
--- gold/powerpc.cc	1 Nov 2012 23:27:00 -0000	1.67
+++ gold/powerpc.cc	5 Nov 2012 00:39:16 -0000
@@ -58,7 +58,6 @@ class Powerpc_relobj : public Sized_relo
 {
 public:
   typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
-  typedef typename elfcpp::Elf_types<size>::Elf_Off Offset;
   typedef Unordered_set<Section_id, Section_id_hash> Section_refs;
   typedef Unordered_map<Address, Section_refs> Access_from;
 
@@ -190,9 +189,17 @@ public:
 		  const unsigned char* prelocs,
 		  const unsigned char* plocal_syms);
 
+  // Perform the Sized_relobj_file method, then set up opd info from
+  // .opd relocs.
   void
   do_read_relocs(Read_relocs_data*);
 
+  // Set up some symbols, then perform Sized_relobj_file method.
+  // Occurs after garbage collection, which is why opd info can't be
+  // set up here.
+  void
+  do_scan_relocs(Symbol_table*, Layout*, Read_relocs_data*);
+
   bool
   do_find_special_sections(Read_symbols_data* sd);
 
@@ -224,7 +231,7 @@ private:
     unsigned int shndx;
     bool discard : 1;
     bool gc_mark : 1;
-    Offset off;
+    Address off;
   };
 
   // Return index into opd_ent_ array for .opd entry at OFF.
@@ -449,6 +456,10 @@ class Target_powerpc : public Sized_targ
     return this->got_;
   }
 
+  // Get the GOT section, creating it if necessary.
+  Output_data_got_powerpc<size, big_endian>*
+  got_section(Symbol_table*, Layout*);
+
   Object*
   do_make_elf_object(const std::string&, Input_file*, off_t,
 		     const elfcpp::Ehdr<size, big_endian>&);
@@ -694,10 +705,6 @@ class Target_powerpc : public Sized_targ
     return tls::TLSOPT_TO_LE;
   }
 
-  // Get the GOT section, creating it if necessary.
-  Output_data_got_powerpc<size, big_endian>*
-  got_section(Symbol_table*, Layout*);
-
   // Create glink.
   void
   make_glink_section(Layout*);
@@ -1374,6 +1381,57 @@ Powerpc_relobj<size, big_endian>::do_rea
     }
 }
 
+// Set up some symbols, then perform Sized_relobj_file method.
+
+template<int size, bool big_endian>
+void
+Powerpc_relobj<size, big_endian>::do_scan_relocs(Symbol_table* symtab,
+						 Layout* layout,
+						 Read_relocs_data* rd)
+{
+  if (size == 32)
+    {
+      // Define a weak hidden _GLOBAL_OFFSET_TABLE_ to ensure it isn't
+      // seen as undefined when scanning relocs (and thus requires
+      // non-relative dynamic relocs).  The proper value will be
+      // updated later.
+      Symbol *gotsym = symtab->lookup("_GLOBAL_OFFSET_TABLE_", NULL);
+      if (gotsym != NULL && gotsym->is_undefined())
+	{
+	  Target_powerpc<size, big_endian>* target =
+	    static_cast<Target_powerpc<size, big_endian>*>(
+		parameters->sized_target<size, big_endian>());
+	  Output_data_got_powerpc<size, big_endian>* got
+	    = target->got_section(symtab, layout);
+	  symtab->define_in_output_data("_GLOBAL_OFFSET_TABLE_", NULL,
+					Symbol_table::PREDEFINED,
+					got, 0, 0,
+					elfcpp::STT_OBJECT,
+					elfcpp::STB_WEAK,
+					elfcpp::STV_HIDDEN, 0,
+					false, false);
+	}
+
+      // Define _SDA_BASE_ at the start of the .sdata section + 32768.
+      Symbol *sdasym = symtab->lookup("_SDA_BASE_", NULL);
+      if (sdasym != NULL && sdasym->is_undefined())
+	{
+	  Output_data_space* sdata = new Output_data_space(4, "** sdata");
+	  Output_section* os
+	    = layout->add_output_section_data(".sdata", 0,
+					      elfcpp::SHF_ALLOC
+					      | elfcpp::SHF_WRITE,
+					      sdata, ORDER_SMALL_DATA, false);
+	  symtab->define_in_output_data("_SDA_BASE_", NULL,
+					Symbol_table::PREDEFINED,
+					os, 32768, 0, elfcpp::STT_OBJECT,
+					elfcpp::STB_LOCAL, elfcpp::STV_HIDDEN,
+					0, false, false);
+	}
+    }
+  Sized_relobj_file<size, big_endian>::do_scan_relocs(symtab, layout, rd);
+}
+
 // Set up PowerPC target specific relobj.
 
 template<int size, bool big_endian>
@@ -1459,7 +1517,7 @@ public:
 
   // Offset of base used to access the GOT/TOC.
   // The got/toc pointer reg will be set to this value.
-  typename elfcpp::Elf_types<size>::Elf_Off
+  Valtype
   got_base_offset(const Powerpc_relobj<size, big_endian>* object) const
   {
     if (size == 32)
@@ -4038,42 +4096,6 @@ Target_powerpc<size, big_endian>::scan_r
       return;
     }
 
-  if (size == 32)
-    {
-      // Define a weak hidden _GLOBAL_OFFSET_TABLE_ to ensure it isn't
-      // seen as undefined when scanning relocs (and thus requires
-      // non-relative dynamic relocs).  The proper value will be
-      // updated later.
-      Symbol *gotsym = symtab->lookup("_GLOBAL_OFFSET_TABLE_", NULL);
-      if (gotsym != NULL && gotsym->is_undefined())
-	symtab->define_in_output_data("_GLOBAL_OFFSET_TABLE_", NULL,
-				      Symbol_table::PREDEFINED,
-				      this->got_section(symtab, layout), 0, 0,
-				      elfcpp::STT_OBJECT,
-				      elfcpp::STB_WEAK,
-				      elfcpp::STV_HIDDEN, 0,
-				      false, false);
-
-      static Output_data_space* sdata;
-
-      // Define _SDA_BASE_ at the start of the .sdata section.
-      if (sdata == NULL)
-	{
-	  // layout->find_output_section(".sdata") == NULL
-	  sdata = new Output_data_space(4, "** sdata");
-	  Output_section* os
-	    = layout->add_output_section_data(".sdata", 0,
-					      elfcpp::SHF_ALLOC
-					      | elfcpp::SHF_WRITE,
-					      sdata, ORDER_SMALL_DATA, false);
-	  symtab->define_in_output_data("_SDA_BASE_", NULL,
-					Symbol_table::PREDEFINED,
-					os, 32768, 0, elfcpp::STT_OBJECT,
-					elfcpp::STB_LOCAL, elfcpp::STV_HIDDEN,
-					0, false, false);
-	}
-    }
-
   gold::scan_relocs<size, big_endian, Powerpc, elfcpp::SHT_RELA, Scan>(
     symtab,
     layout,

-- 
Alan Modra
Australia Development Lab, IBM