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.  We normally put the
  68 // larger common symbols first.  This can be changed by using
  69 // --sort-commons, which tells the linker to sort by alignment.
  70
  71 template<int size>
  72 class Sort_commons
  73 {
  74  public:
  75   Sort_commons(const Symbol_table* symtab,
  76                Symbol_table::Sort_commons_order sort_order)
  77     : symtab_(symtab), sort_order_(sort_order)
  78   { }
  79
  80   bool operator()(const Symbol* a, const Symbol* b) const;
  81
  82  private:
  83   // The symbol table.
  84   const Symbol_table* symtab_;
  85   // How to sort.
  86   Symbol_table::Sort_commons_order sort_order_;
  87 };
  88
  89 template<int size>
  90 bool
  91 Sort_commons<size>::operator()(const Symbol* pa, const Symbol* pb) const
  92 {
  93   if (pa == NULL)
  94     {
  95       if (pb == NULL)
  96         {
  97           // Stabilize sort.  The order really doesn't matter, because
  98           // these entries will be discarded, but we want to return
  99           // the same result every time we compare pa and pb.
 100           return pa < pb;
 101         }
 102       return false;
 103     }
 104   if (pb == NULL)
 105     return true;
 106
 107   const Symbol_table* symtab = this->symtab_;
 108   const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
 109   const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
 110
 111   // The size.
 112   typename Sized_symbol<size>::Size_type sa = psa->symsize();
 113   typename Sized_symbol<size>::Size_type sb = psb->symsize();
 114
 115   // The alignment.
 116   typename Sized_symbol<size>::Value_type aa = psa->value();
 117   typename Sized_symbol<size>::Value_type ab = psb->value();
 118
 119   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_DESCENDING)
 120     {
 121       if (aa < ab)
 122         return false;
 123       else if (ab < aa)
 124         return true;
 125     }
 126   else if (this->sort_order_
 127            == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_ASCENDING)
 128     {
 129       if (aa < ab)
 130         return true;
 131       else if (ab < aa)
 132         return false;
 133     }
 134   else
 135     gold_assert(this->sort_order_
 136                 == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING);
 137
 138   // Sort by descending size.
 139   if (sa < sb)
 140     return false;
 141   else if (sb < sa)
 142     return true;
 143
 144   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING)
 145     {
 146       // When the symbols are the same size, we sort them by
 147       // alignment, largest alignment first.
 148       if (aa < ab)
 149         return false;
 150       else if (ab < aa)
 151         return true;
 152     }
 153
 154   // Otherwise we stabilize the sort by sorting by name.
 155   return strcmp(psa->name(), psb->name()) < 0;
 156 }
 157
 158 // Allocate the common symbols.
 159
 160 void
 161 Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
 162 {
 163   Sort_commons_order sort_order;
 164   if (!parameters->options().user_set_sort_common())
 165     sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 166   else
 167     {
 168       const char* order = parameters->options().sort_common();
 169       if (*order == '\0' || strcmp(order, "descending") == 0)
 170         sort_order = SORT_COMMONS_BY_ALIGNMENT_DESCENDING;
 171       else if (strcmp(order, "ascending") == 0)
 172         sort_order = SORT_COMMONS_BY_ALIGNMENT_ASCENDING;
 173       else
 174         {
 175           gold_error("invalid --sort-common argument: %s", order);
 176           sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 177         }
 178     }
 179
 180   if (parameters->target().get_size() == 32)
 181     {
 182 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 183       this->do_allocate_commons<32>(layout, mapfile, sort_order);
 184 #else
 185       gold_unreachable();
 186 #endif
 187     }
 188   else if (parameters->target().get_size() == 64)
 189     {
 190 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 191       this->do_allocate_commons<64>(layout, mapfile, sort_order);
 192 #else
 193       gold_unreachable();
 194 #endif
 195     }
 196   else
 197     gold_unreachable();
 198 }
 199
 200 // Allocated the common symbols, sized version.
 201
 202 template<int size>
 203 void
 204 Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile,
 205                                   Sort_commons_order sort_order)
 206 {
 207   if (!this->commons_.empty())
 208     this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
 209                                          &this->commons_, mapfile,
 210                                          sort_order);
 211   if (!this->tls_commons_.empty())
 212     this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
 213                                          &this->tls_commons_, mapfile,
 214                                          sort_order);
 215   if (!this->small_commons_.empty())
 216     this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
 217                                          &this->small_commons_, mapfile,
 218                                          sort_order);
 219   if (!this->large_commons_.empty())
 220     this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
 221                                          &this->large_commons_, mapfile,
 222                                          sort_order);
 223 }
 224
 225 // Allocate the common symbols in a list.  IS_TLS indicates whether
 226 // these are TLS common symbols.
 227
 228 template<int size>
 229 void
 230 Symbol_table::do_allocate_commons_list(
 231     Layout* layout,
 232     Commons_section_type commons_section_type,
 233     Commons_type* commons,
 234     Mapfile* mapfile,
 235     Sort_commons_order sort_order)
 236 {
 237   typedef typename Sized_symbol<size>::Value_type Value_type;
 238   typedef typename Sized_symbol<size>::Size_type Size_type;
 239
 240   // We've kept a list of all the common symbols.  But the symbol may
 241   // have been resolved to a defined symbol by now.  And it may be a
 242   // forwarder.  First remove all non-common symbols.
 243   bool any = false;
 244   uint64_t addralign = 0;
 245   for (Commons_type::iterator p = commons->begin();
 246        p != commons->end();
 247        ++p)
 248     {
 249       Symbol* sym = *p;
 250       if (sym->is_forwarder())
 251         {
 252           sym = this->resolve_forwards(sym);
 253           *p = sym;
 254         }
 255       if (!sym->is_common())
 256         *p = NULL;
 257       else
 258         {
 259           any = true;
 260           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 261           if (ssym->value() > addralign)
 262             addralign = ssym->value();
 263         }
 264     }
 265   if (!any)
 266     return;
 267
 268   // Sort the common symbols.
 269   std::sort(commons->begin(), commons->end(),
 270             Sort_commons<size>(this, sort_order));
 271
 272   // Place them in a newly allocated BSS section.
 273   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 274   const char* name;
 275   const char* ds_name;
 276   switch (commons_section_type)
 277     {
 278     case COMMONS_NORMAL:
 279       name = ".bss";
 280       ds_name = "** common";
 281       break;
 282     case COMMONS_TLS:
 283       flags |= elfcpp::SHF_TLS;
 284       name = ".tbss";
 285       ds_name = "** tls common";
 286       break;
 287     case COMMONS_SMALL:
 288       flags |= parameters->target().small_common_section_flags();
 289       name = ".sbss";
 290       ds_name = "** small common";
 291       break;
 292     case COMMONS_LARGE:
 293       flags |= parameters->target().large_common_section_flags();
 294       name = ".lbss";
 295       ds_name = "** large common";
 296       break;
 297     default:
 298       gold_unreachable();
 299     }
 300
 301   Output_data_space *poc = new Output_data_space(addralign, ds_name);
 302   Output_section *os = layout->add_output_section_data(name,
 303                                                        elfcpp::SHT_NOBITS,
 304                                                        flags, poc, false,
 305                                                        false, false, false);
 306   if (os != NULL)
 307     {
 308       if (commons_section_type == COMMONS_SMALL)
 309         os->set_is_small_section();
 310       else if (commons_section_type == COMMONS_LARGE)
 311         os->set_is_large_section();
 312     }
 313
 314   // Allocate them all.
 315
 316   off_t off = 0;
 317   for (Commons_type::iterator p = commons->begin();
 318        p != commons->end();
 319        ++p)
 320     {
 321       Symbol* sym = *p;
 322       if (sym == NULL)
 323         break;
 324
 325       // Because we followed forwarding symbols above, but we didn't
 326       // do it reliably before adding symbols to the list, it is
 327       // possible for us to have the same symbol on the list twice.
 328       // This can happen in the horrible case where a program defines
 329       // a common symbol with the same name as a versioned libc
 330       // symbol.  That will show up here as a symbol which has already
 331       // been allocated and is therefore no longer a common symbol.
 332       if (!sym->is_common())
 333         continue;
 334
 335       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 336
 337       // Record the symbol in the map file now, before we change its
 338       // value.  Pass the size in separately so that we don't have to
 339       // templatize the map code, which is not performance sensitive.
 340       if (mapfile != NULL)
 341         mapfile->report_allocate_common(sym, ssym->symsize());
 342
 343       off = align_address(off, ssym->value());
 344       ssym->allocate_common(poc, off);
 345       off += ssym->symsize();
 346     }
 347
 348   poc->set_current_data_size(off);
 349
 350   commons->clear();
 351 }
 352
 353 } // End namespace gold.