gold/common.cc

   1 // common.cc -- handle common symbols for gold
   2
   3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #include "gold.h"
  24
  25 #include <algorithm>
  26
  27 #include "workqueue.h"
  28 #include "mapfile.h"
  29 #include "layout.h"
  30 #include "output.h"
  31 #include "symtab.h"
  32 #include "common.h"
  33
  34 namespace gold
  35 {
  36
  37 // Allocate_commons_task methods.
  38
  39 // This task allocates the common symbols.  We need a lock on the
  40 // symbol table.
  41
  42 Task_token*
  43 Allocate_commons_task::is_runnable()
  44 {
  45   if (!this->symtab_lock_->is_writable())
  46     return this->symtab_lock_;
  47   return NULL;
  48 }
  49
  50 // Return the locks we hold: one on the symbol table, and one blocker.
  51
  52 void
  53 Allocate_commons_task::locks(Task_locker* tl)
  54 {
  55   tl->add(this, this->blocker_);
  56   tl->add(this, this->symtab_lock_);
  57 }
  58
  59 // Allocate the common symbols.
  60
  61 void
  62 Allocate_commons_task::run(Workqueue*)
  63 {
  64   this->symtab_->allocate_commons(this->layout_, this->mapfile_);
  65 }
  66
  67 // This class is used to sort the common symbol by size.  We put the
  68 // larger common symbols first.
  69
  70 template<int size>
  71 class Sort_commons
  72 {
  73  public:
  74   Sort_commons(const Symbol_table* symtab)
  75     : symtab_(symtab)
  76   { }
  77
  78   bool operator()(const Symbol* a, const Symbol* b) const;
  79
  80  private:
  81   const Symbol_table* symtab_;
  82 };
  83
  84 template<int size>
  85 bool
  86 Sort_commons<size>::operator()(const Symbol* pa, const Symbol* pb) const
  87 {
  88   if (pa == NULL)
  89     return false;
  90   if (pb == NULL)
  91     return true;
  92
  93   const Symbol_table* symtab = this->symtab_;
  94   const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
  95   const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
  96
  97   // Sort by largest size first.
  98   typename Sized_symbol<size>::Size_type sa = psa->symsize();
  99   typename Sized_symbol<size>::Size_type sb = psb->symsize();
 100   if (sa < sb)
 101     return false;
 102   else if (sb < sa)
 103     return true;
 104
 105   // When the symbols are the same size, we sort them by alignment,
 106   // largest alignment first.
 107   typename Sized_symbol<size>::Value_type va = psa->value();
 108   typename Sized_symbol<size>::Value_type vb = psb->value();
 109   if (va < vb)
 110     return false;
 111   else if (vb < va)
 112     return true;
 113
 114   // Otherwise we stabilize the sort by sorting by name.
 115   return strcmp(psa->name(), psb->name()) < 0;
 116 }
 117
 118 // Allocate the common symbols.
 119
 120 void
 121 Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
 122 {
 123   if (parameters->target().get_size() == 32)
 124     {
 125 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 126       this->do_allocate_commons<32>(layout, mapfile);
 127 #else
 128       gold_unreachable();
 129 #endif
 130     }
 131   else if (parameters->target().get_size() == 64)
 132     {
 133 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 134       this->do_allocate_commons<64>(layout, mapfile);
 135 #else
 136       gold_unreachable();
 137 #endif
 138     }
 139   else
 140     gold_unreachable();
 141 }
 142
 143 // Allocated the common symbols, sized version.
 144
 145 template<int size>
 146 void
 147 Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile)
 148 {
 149   if (!this->commons_.empty())
 150     this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
 151                                          &this->commons_, mapfile);
 152   if (!this->tls_commons_.empty())
 153     this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
 154                                          &this->tls_commons_, mapfile);
 155   if (!this->small_commons_.empty())
 156     this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
 157                                          &this->small_commons_, mapfile);
 158   if (!this->large_commons_.empty())
 159     this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
 160                                          &this->large_commons_, mapfile);
 161 }
 162
 163 // Allocate the common symbols in a list.  IS_TLS indicates whether
 164 // these are TLS common symbols.
 165
 166 template<int size>
 167 void
 168 Symbol_table::do_allocate_commons_list(
 169     Layout* layout,
 170     Commons_section_type commons_section_type,
 171     Commons_type* commons,
 172     Mapfile* mapfile)
 173 {
 174   typedef typename Sized_symbol<size>::Value_type Value_type;
 175   typedef typename Sized_symbol<size>::Size_type Size_type;
 176
 177   // We've kept a list of all the common symbols.  But the symbol may
 178   // have been resolved to a defined symbol by now.  And it may be a
 179   // forwarder.  First remove all non-common symbols.
 180   bool any = false;
 181   uint64_t addralign = 0;
 182   for (Commons_type::iterator p = commons->begin();
 183        p != commons->end();
 184        ++p)
 185     {
 186       Symbol* sym = *p;
 187       if (sym->is_forwarder())
 188         {
 189           sym = this->resolve_forwards(sym);
 190           *p = sym;
 191         }
 192       if (!sym->is_common())
 193         *p = NULL;
 194       else
 195         {
 196           any = true;
 197           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 198           if (ssym->value() > addralign)
 199             addralign = ssym->value();
 200         }
 201     }
 202   if (!any)
 203     return;
 204
 205   // Sort the common symbols by size, so that they pack better into
 206   // memory.
 207   std::sort(commons->begin(), commons->end(),
 208             Sort_commons<size>(this));
 209
 210   // Place them in a newly allocated BSS section.
 211   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 212   const char* name;
 213   const char* ds_name;
 214   switch (commons_section_type)
 215     {
 216     case COMMONS_NORMAL:
 217       name = ".bss";
 218       ds_name = "** common";
 219       break;
 220     case COMMONS_TLS:
 221       flags |= elfcpp::SHF_TLS;
 222       name = ".tbss";
 223       ds_name = "** tls common";
 224       break;
 225     case COMMONS_SMALL:
 226       flags |= parameters->target().small_common_section_flags();
 227       name = ".sbss";
 228       ds_name = "** small common";
 229       break;
 230     case COMMONS_LARGE:
 231       flags |= parameters->target().large_common_section_flags();
 232       name = ".lbss";
 233       ds_name = "** large common";
 234       break;
 235     default:
 236       gold_unreachable();
 237     }
 238
 239   Output_data_space *poc = new Output_data_space(addralign, ds_name);
 240   Output_section *os = layout->add_output_section_data(name,
 241                                                        elfcpp::SHT_NOBITS,
 242                                                        flags, poc, false);
 243   if (os != NULL)
 244     {
 245       if (commons_section_type == COMMONS_SMALL)
 246         os->set_is_small_section();
 247       else if (commons_section_type == COMMONS_LARGE)
 248         os->set_is_large_section();
 249     }
 250
 251   // Allocate them all.
 252
 253   off_t off = 0;
 254   for (Commons_type::iterator p = commons->begin();
 255        p != commons->end();
 256        ++p)
 257     {
 258       Symbol* sym = *p;
 259       if (sym == NULL)
 260         break;
 261       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 262
 263       // Record the symbol in the map file now, before we change its
 264       // value.  Pass the size in separately so that we don't have to
 265       // templatize the map code, which is not performance sensitive.
 266       if (mapfile != NULL)
 267         mapfile->report_allocate_common(sym, ssym->symsize());
 268
 269       off = align_address(off, ssym->value());
 270       ssym->allocate_common(poc, off);
 271       off += ssym->symsize();
 272     }
 273
 274   poc->set_current_data_size(off);
 275
 276   commons->clear();
 277 }
 278
 279 } // End namespace gold.