gold/common.cc

   1 // common.cc -- handle common symbols for gold
   2
   3 // Copyright 2006, 2007, 2008, 2009, 2010, 2011, 2012
   4 // Free Software Foundation, Inc.
   5 // Written by Ian Lance Taylor <iant@google.com>.
   6
   7 // This file is part of gold.
   8
   9 // This program is free software; you can redistribute it and/or modify
  10 // it under the terms of the GNU General Public License as published by
  11 // the Free Software Foundation; either version 3 of the License, or
  12 // (at your option) any later version.
  13
  14 // This program is distributed in the hope that it will be useful,
  15 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 // GNU General Public License for more details.
  18
  19 // You should have received a copy of the GNU General Public License
  20 // along with this program; if not, write to the Free Software
  21 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  22 // MA 02110-1301, USA.
  23
  24 #include "gold.h"
  25
  26 #include <algorithm>
  27
  28 #include "workqueue.h"
  29 #include "mapfile.h"
  30 #include "layout.h"
  31 #include "output.h"
  32 #include "symtab.h"
  33 #include "common.h"
  34
  35 namespace gold
  36 {
  37
  38 // Allocate_commons_task methods.
  39
  40 // This task allocates the common symbols.  We arrange to run it
  41 // before anything else which needs to access the symbol table.
  42
  43 Task_token*
  44 Allocate_commons_task::is_runnable()
  45 {
  46   return NULL;
  47 }
  48
  49 // Release a blocker.
  50
  51 void
  52 Allocate_commons_task::locks(Task_locker* tl)
  53 {
  54   tl->add(this, this->blocker_);
  55 }
  56
  57 // Allocate the common symbols.
  58
  59 void
  60 Allocate_commons_task::run(Workqueue*)
  61 {
  62   this->symtab_->allocate_commons(this->layout_, this->mapfile_);
  63 }
  64
  65 // This class is used to sort the common symbol.  We normally put the
  66 // larger common symbols first.  This can be changed by using
  67 // --sort-commons, which tells the linker to sort by alignment.
  68
  69 template<int size>
  70 class Sort_commons
  71 {
  72  public:
  73   Sort_commons(const Symbol_table* symtab,
  74                Symbol_table::Sort_commons_order sort_order)
  75     : symtab_(symtab), sort_order_(sort_order)
  76   { }
  77
  78   bool operator()(const Symbol* a, const Symbol* b) const;
  79
  80  private:
  81   // The symbol table.
  82   const Symbol_table* symtab_;
  83   // How to sort.
  84   Symbol_table::Sort_commons_order sort_order_;
  85 };
  86
  87 template<int size>
  88 bool
  89 Sort_commons<size>::operator()(const Symbol* pa, const Symbol* pb) const
  90 {
  91   if (pa == NULL)
  92     return false;
  93   if (pb == NULL)
  94     return true;
  95
  96   const Symbol_table* symtab = this->symtab_;
  97   const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
  98   const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
  99
 100   // The size.
 101   typename Sized_symbol<size>::Size_type sa = psa->symsize();
 102   typename Sized_symbol<size>::Size_type sb = psb->symsize();
 103
 104   // The alignment.
 105   typename Sized_symbol<size>::Value_type aa = psa->value();
 106   typename Sized_symbol<size>::Value_type ab = psb->value();
 107
 108   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_DESCENDING)
 109     {
 110       if (aa < ab)
 111         return false;
 112       else if (ab < aa)
 113         return true;
 114     }
 115   else if (this->sort_order_
 116            == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_ASCENDING)
 117     {
 118       if (aa < ab)
 119         return true;
 120       else if (ab < aa)
 121         return false;
 122     }
 123   else
 124     gold_assert(this->sort_order_
 125                 == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING);
 126
 127   // Sort by descending size.
 128   if (sa < sb)
 129     return false;
 130   else if (sb < sa)
 131     return true;
 132
 133   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING)
 134     {
 135       // When the symbols are the same size, we sort them by
 136       // alignment, largest alignment first.
 137       if (aa < ab)
 138         return false;
 139       else if (ab < aa)
 140         return true;
 141     }
 142
 143   // Otherwise we stabilize the sort by sorting by name.
 144   return strcmp(psa->name(), psb->name()) < 0;
 145 }
 146
 147 // Allocate the common symbols.
 148
 149 void
 150 Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
 151 {
 152   Sort_commons_order sort_order;
 153   if (!parameters->options().user_set_sort_common())
 154     sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 155   else
 156     {
 157       const char* order = parameters->options().sort_common();
 158       if (*order == '\0' || strcmp(order, "descending") == 0)
 159         sort_order = SORT_COMMONS_BY_ALIGNMENT_DESCENDING;
 160       else if (strcmp(order, "ascending") == 0)
 161         sort_order = SORT_COMMONS_BY_ALIGNMENT_ASCENDING;
 162       else
 163         {
 164           gold_error("invalid --sort-common argument: %s", order);
 165           sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 166         }
 167     }
 168
 169   if (parameters->target().get_size() == 32)
 170     {
 171 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 172       this->do_allocate_commons<32>(layout, mapfile, sort_order);
 173 #else
 174       gold_unreachable();
 175 #endif
 176     }
 177   else if (parameters->target().get_size() == 64)
 178     {
 179 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 180       this->do_allocate_commons<64>(layout, mapfile, sort_order);
 181 #else
 182       gold_unreachable();
 183 #endif
 184     }
 185   else
 186     gold_unreachable();
 187 }
 188
 189 // Allocated the common symbols, sized version.
 190
 191 template<int size>
 192 void
 193 Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile,
 194                                   Sort_commons_order sort_order)
 195 {
 196   if (!this->commons_.empty())
 197     this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
 198                                          &this->commons_, mapfile,
 199                                          sort_order);
 200   if (!this->tls_commons_.empty())
 201     this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
 202                                          &this->tls_commons_, mapfile,
 203                                          sort_order);
 204   if (!this->small_commons_.empty())
 205     this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
 206                                          &this->small_commons_, mapfile,
 207                                          sort_order);
 208   if (!this->large_commons_.empty())
 209     this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
 210                                          &this->large_commons_, mapfile,
 211                                          sort_order);
 212 }
 213
 214 // Allocate the common symbols in a list.  IS_TLS indicates whether
 215 // these are TLS common symbols.
 216
 217 template<int size>
 218 void
 219 Symbol_table::do_allocate_commons_list(
 220     Layout* layout,
 221     Commons_section_type commons_section_type,
 222     Commons_type* commons,
 223     Mapfile* mapfile,
 224     Sort_commons_order sort_order)
 225 {
 226   // We've kept a list of all the common symbols.  But the symbol may
 227   // have been resolved to a defined symbol by now.  And it may be a
 228   // forwarder.  First remove all non-common symbols.
 229   bool any = false;
 230   uint64_t addralign = 0;
 231   for (Commons_type::iterator p = commons->begin();
 232        p != commons->end();
 233        ++p)
 234     {
 235       Symbol* sym = *p;
 236       if (sym->is_forwarder())
 237         {
 238           sym = this->resolve_forwards(sym);
 239           *p = sym;
 240         }
 241       if (!sym->is_common())
 242         *p = NULL;
 243       else
 244         {
 245           any = true;
 246           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 247           if (ssym->value() > addralign)
 248             addralign = ssym->value();
 249         }
 250     }
 251   if (!any)
 252     return;
 253
 254   // Sort the common symbols.
 255   std::sort(commons->begin(), commons->end(),
 256             Sort_commons<size>(this, sort_order));
 257
 258   // Place them in a newly allocated BSS section.
 259   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 260   const char* name;
 261   const char* ds_name;
 262   switch (commons_section_type)
 263     {
 264     case COMMONS_NORMAL:
 265       name = ".bss";
 266       ds_name = "** common";
 267       break;
 268     case COMMONS_TLS:
 269       flags |= elfcpp::SHF_TLS;
 270       name = ".tbss";
 271       ds_name = "** tls common";
 272       break;
 273     case COMMONS_SMALL:
 274       flags |= parameters->target().small_common_section_flags();
 275       name = ".sbss";
 276       ds_name = "** small common";
 277       break;
 278     case COMMONS_LARGE:
 279       flags |= parameters->target().large_common_section_flags();
 280       name = ".lbss";
 281       ds_name = "** large common";
 282       break;
 283     default:
 284       gold_unreachable();
 285     }
 286
 287   Output_data_space* poc;
 288   Output_section* os;
 289
 290   if (!parameters->incremental_update())
 291     {
 292       poc = new Output_data_space(addralign, ds_name);
 293       os = layout->add_output_section_data(name, elfcpp::SHT_NOBITS, flags,
 294                                            poc, ORDER_INVALID, false);
 295     }
 296   else
 297     {
 298       // When doing an incremental update, we need to allocate each common
 299       // directly from the output section's free list.
 300       poc = NULL;
 301       os = layout->find_output_section(name);
 302     }
 303
 304   if (os != NULL)
 305     {
 306       if (commons_section_type == COMMONS_SMALL)
 307         os->set_is_small_section();
 308       else if (commons_section_type == COMMONS_LARGE)
 309         os->set_is_large_section();
 310     }
 311
 312   // Allocate them all.
 313
 314   off_t off = 0;
 315   for (Commons_type::iterator p = commons->begin();
 316        p != commons->end();
 317        ++p)
 318     {
 319       Symbol* sym = *p;
 320       if (sym == NULL)
 321         break;
 322
 323       // Because we followed forwarding symbols above, but we didn't
 324       // do it reliably before adding symbols to the list, it is
 325       // possible for us to have the same symbol on the list twice.
 326       // This can happen in the horrible case where a program defines
 327       // a common symbol with the same name as a versioned libc
 328       // symbol.  That will show up here as a symbol which has already
 329       // been allocated and is therefore no longer a common symbol.
 330       if (!sym->is_common())
 331         continue;
 332
 333       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 334
 335       // Record the symbol in the map file now, before we change its
 336       // value.  Pass the size in separately so that we don't have to
 337       // templatize the map code, which is not performance sensitive.
 338       if (mapfile != NULL)
 339         mapfile->report_allocate_common(sym, ssym->symsize());
 340
 341       if (poc != NULL)
 342         {
 343           off = align_address(off, ssym->value());
 344           ssym->allocate_common(poc, off);
 345           off += ssym->symsize();
 346         }
 347       else
 348         {
 349           // For an incremental update, allocate from the free list.
 350           off = os->allocate(ssym->symsize(), ssym->value());
 351           if (off == -1)
 352             gold_fallback(_("out of patch space in section %s; "
 353                             "relink with --incremental-full"),
 354                           os->name());
 355           ssym->allocate_common(os, off);
 356         }
 357     }
 358
 359   if (poc != NULL)
 360     poc->set_current_data_size(off);
 361
 362   commons->clear();
 363 }
 364
 365 } // End namespace gold.