gold/common.cc

   1 // common.cc -- handle common symbols for gold
   2
   3 // Copyright 2006, 2007, 2008, 2009, 2010 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 arrange to run it
  40 // before anything else which needs to access the symbol table.
  41
  42 Task_token*
  43 Allocate_commons_task::is_runnable()
  44 {
  45   return NULL;
  46 }
  47
  48 // Release a blocker.
  49
  50 void
  51 Allocate_commons_task::locks(Task_locker* tl)
  52 {
  53   tl->add(this, this->blocker_);
  54 }
  55
  56 // Allocate the common symbols.
  57
  58 void
  59 Allocate_commons_task::run(Workqueue*)
  60 {
  61   this->symtab_->allocate_commons(this->layout_, this->mapfile_);
  62 }
  63
  64 // This class is used to sort the common symbol.  We normally put the
  65 // larger common symbols first.  This can be changed by using
  66 // --sort-commons, which tells the linker to sort by alignment.
  67
  68 template<int size>
  69 class Sort_commons
  70 {
  71  public:
  72   Sort_commons(const Symbol_table* symtab,
  73                Symbol_table::Sort_commons_order sort_order)
  74     : symtab_(symtab), sort_order_(sort_order)
  75   { }
  76
  77   bool operator()(const Symbol* a, const Symbol* b) const;
  78
  79  private:
  80   // The symbol table.
  81   const Symbol_table* symtab_;
  82   // How to sort.
  83   Symbol_table::Sort_commons_order sort_order_;
  84 };
  85
  86 template<int size>
  87 bool
  88 Sort_commons<size>::operator()(const Symbol* pa, const Symbol* pb) const
  89 {
  90   if (pa == NULL)
  91     return false;
  92   if (pb == NULL)
  93     return true;
  94
  95   const Symbol_table* symtab = this->symtab_;
  96   const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
  97   const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
  98
  99   // The size.
 100   typename Sized_symbol<size>::Size_type sa = psa->symsize();
 101   typename Sized_symbol<size>::Size_type sb = psb->symsize();
 102
 103   // The alignment.
 104   typename Sized_symbol<size>::Value_type aa = psa->value();
 105   typename Sized_symbol<size>::Value_type ab = psb->value();
 106
 107   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_DESCENDING)
 108     {
 109       if (aa < ab)
 110         return false;
 111       else if (ab < aa)
 112         return true;
 113     }
 114   else if (this->sort_order_
 115            == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_ASCENDING)
 116     {
 117       if (aa < ab)
 118         return true;
 119       else if (ab < aa)
 120         return false;
 121     }
 122   else
 123     gold_assert(this->sort_order_
 124                 == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING);
 125
 126   // Sort by descending size.
 127   if (sa < sb)
 128     return false;
 129   else if (sb < sa)
 130     return true;
 131
 132   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING)
 133     {
 134       // When the symbols are the same size, we sort them by
 135       // alignment, largest alignment first.
 136       if (aa < ab)
 137         return false;
 138       else if (ab < aa)
 139         return true;
 140     }
 141
 142   // Otherwise we stabilize the sort by sorting by name.
 143   return strcmp(psa->name(), psb->name()) < 0;
 144 }
 145
 146 // Allocate the common symbols.
 147
 148 void
 149 Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
 150 {
 151   Sort_commons_order sort_order;
 152   if (!parameters->options().user_set_sort_common())
 153     sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 154   else
 155     {
 156       const char* order = parameters->options().sort_common();
 157       if (*order == '\0' || strcmp(order, "descending") == 0)
 158         sort_order = SORT_COMMONS_BY_ALIGNMENT_DESCENDING;
 159       else if (strcmp(order, "ascending") == 0)
 160         sort_order = SORT_COMMONS_BY_ALIGNMENT_ASCENDING;
 161       else
 162         {
 163           gold_error("invalid --sort-common argument: %s", order);
 164           sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 165         }
 166     }
 167
 168   if (parameters->target().get_size() == 32)
 169     {
 170 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 171       this->do_allocate_commons<32>(layout, mapfile, sort_order);
 172 #else
 173       gold_unreachable();
 174 #endif
 175     }
 176   else if (parameters->target().get_size() == 64)
 177     {
 178 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 179       this->do_allocate_commons<64>(layout, mapfile, sort_order);
 180 #else
 181       gold_unreachable();
 182 #endif
 183     }
 184   else
 185     gold_unreachable();
 186 }
 187
 188 // Allocated the common symbols, sized version.
 189
 190 template<int size>
 191 void
 192 Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile,
 193                                   Sort_commons_order sort_order)
 194 {
 195   if (!this->commons_.empty())
 196     this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
 197                                          &this->commons_, mapfile,
 198                                          sort_order);
 199   if (!this->tls_commons_.empty())
 200     this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
 201                                          &this->tls_commons_, mapfile,
 202                                          sort_order);
 203   if (!this->small_commons_.empty())
 204     this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
 205                                          &this->small_commons_, mapfile,
 206                                          sort_order);
 207   if (!this->large_commons_.empty())
 208     this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
 209                                          &this->large_commons_, mapfile,
 210                                          sort_order);
 211 }
 212
 213 // Allocate the common symbols in a list.  IS_TLS indicates whether
 214 // these are TLS common symbols.
 215
 216 template<int size>
 217 void
 218 Symbol_table::do_allocate_commons_list(
 219     Layout* layout,
 220     Commons_section_type commons_section_type,
 221     Commons_type* commons,
 222     Mapfile* mapfile,
 223     Sort_commons_order sort_order)
 224 {
 225   typedef typename Sized_symbol<size>::Value_type Value_type;
 226   typedef typename Sized_symbol<size>::Size_type Size_type;
 227
 228   // We've kept a list of all the common symbols.  But the symbol may
 229   // have been resolved to a defined symbol by now.  And it may be a
 230   // forwarder.  First remove all non-common symbols.
 231   bool any = false;
 232   uint64_t addralign = 0;
 233   for (Commons_type::iterator p = commons->begin();
 234        p != commons->end();
 235        ++p)
 236     {
 237       Symbol* sym = *p;
 238       if (sym->is_forwarder())
 239         {
 240           sym = this->resolve_forwards(sym);
 241           *p = sym;
 242         }
 243       if (!sym->is_common())
 244         *p = NULL;
 245       else
 246         {
 247           any = true;
 248           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 249           if (ssym->value() > addralign)
 250             addralign = ssym->value();
 251         }
 252     }
 253   if (!any)
 254     return;
 255
 256   // Sort the common symbols.
 257   std::sort(commons->begin(), commons->end(),
 258             Sort_commons<size>(this, sort_order));
 259
 260   // Place them in a newly allocated BSS section.
 261   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 262   const char* name;
 263   const char* ds_name;
 264   switch (commons_section_type)
 265     {
 266     case COMMONS_NORMAL:
 267       name = ".bss";
 268       ds_name = "** common";
 269       break;
 270     case COMMONS_TLS:
 271       flags |= elfcpp::SHF_TLS;
 272       name = ".tbss";
 273       ds_name = "** tls common";
 274       break;
 275     case COMMONS_SMALL:
 276       flags |= parameters->target().small_common_section_flags();
 277       name = ".sbss";
 278       ds_name = "** small common";
 279       break;
 280     case COMMONS_LARGE:
 281       flags |= parameters->target().large_common_section_flags();
 282       name = ".lbss";
 283       ds_name = "** large common";
 284       break;
 285     default:
 286       gold_unreachable();
 287     }
 288
 289   Output_data_space* poc = new Output_data_space(addralign, ds_name);
 290   Output_section* os = layout->add_output_section_data(name,
 291                                                        elfcpp::SHT_NOBITS,
 292                                                        flags, poc,
 293                                                        ORDER_INVALID,
 294                                                        false);
 295   if (os != NULL)
 296     {
 297       if (commons_section_type == COMMONS_SMALL)
 298         os->set_is_small_section();
 299       else if (commons_section_type == COMMONS_LARGE)
 300         os->set_is_large_section();
 301     }
 302
 303   // Allocate them all.
 304
 305   off_t off = 0;
 306   for (Commons_type::iterator p = commons->begin();
 307        p != commons->end();
 308        ++p)
 309     {
 310       Symbol* sym = *p;
 311       if (sym == NULL)
 312         break;
 313
 314       // Because we followed forwarding symbols above, but we didn't
 315       // do it reliably before adding symbols to the list, it is
 316       // possible for us to have the same symbol on the list twice.
 317       // This can happen in the horrible case where a program defines
 318       // a common symbol with the same name as a versioned libc
 319       // symbol.  That will show up here as a symbol which has already
 320       // been allocated and is therefore no longer a common symbol.
 321       if (!sym->is_common())
 322         continue;
 323
 324       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 325
 326       // Record the symbol in the map file now, before we change its
 327       // value.  Pass the size in separately so that we don't have to
 328       // templatize the map code, which is not performance sensitive.
 329       if (mapfile != NULL)
 330         mapfile->report_allocate_common(sym, ssym->symsize());
 331
 332       off = align_address(off, ssym->value());
 333       ssym->allocate_common(poc, off);
 334       off += ssym->symsize();
 335     }
 336
 337   poc->set_current_data_size(off);
 338
 339   commons->clear();
 340 }
 341
 342 } // End namespace gold.