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     {
  92       if (pb == NULL)
  93         {
  94           // Stabilize sort.  The order really doesn't matter, because
  95           // these entries will be discarded, but we want to return
  96           // the same result every time we compare pa and pb.
  97           return pa < pb;
  98         }
  99       return false;
 100     }
 101   if (pb == NULL)
 102     return true;
 103
 104   const Symbol_table* symtab = this->symtab_;
 105   const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
 106   const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
 107
 108   // The size.
 109   typename Sized_symbol<size>::Size_type sa = psa->symsize();
 110   typename Sized_symbol<size>::Size_type sb = psb->symsize();
 111
 112   // The alignment.
 113   typename Sized_symbol<size>::Value_type aa = psa->value();
 114   typename Sized_symbol<size>::Value_type ab = psb->value();
 115
 116   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_DESCENDING)
 117     {
 118       if (aa < ab)
 119         return false;
 120       else if (ab < aa)
 121         return true;
 122     }
 123   else if (this->sort_order_
 124            == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_ASCENDING)
 125     {
 126       if (aa < ab)
 127         return true;
 128       else if (ab < aa)
 129         return false;
 130     }
 131   else
 132     gold_assert(this->sort_order_
 133                 == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING);
 134
 135   // Sort by descending size.
 136   if (sa < sb)
 137     return false;
 138   else if (sb < sa)
 139     return true;
 140
 141   if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING)
 142     {
 143       // When the symbols are the same size, we sort them by
 144       // alignment, largest alignment first.
 145       if (aa < ab)
 146         return false;
 147       else if (ab < aa)
 148         return true;
 149     }
 150
 151   // Otherwise we stabilize the sort by sorting by name.
 152   return strcmp(psa->name(), psb->name()) < 0;
 153 }
 154
 155 // Allocate the common symbols.
 156
 157 void
 158 Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
 159 {
 160   Sort_commons_order sort_order;
 161   if (!parameters->options().user_set_sort_common())
 162     sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 163   else
 164     {
 165       const char* order = parameters->options().sort_common();
 166       if (*order == '\0' || strcmp(order, "descending") == 0)
 167         sort_order = SORT_COMMONS_BY_ALIGNMENT_DESCENDING;
 168       else if (strcmp(order, "ascending") == 0)
 169         sort_order = SORT_COMMONS_BY_ALIGNMENT_ASCENDING;
 170       else
 171         {
 172           gold_error("invalid --sort-common argument: %s", order);
 173           sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
 174         }
 175     }
 176
 177   if (parameters->target().get_size() == 32)
 178     {
 179 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
 180       this->do_allocate_commons<32>(layout, mapfile, sort_order);
 181 #else
 182       gold_unreachable();
 183 #endif
 184     }
 185   else if (parameters->target().get_size() == 64)
 186     {
 187 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
 188       this->do_allocate_commons<64>(layout, mapfile, sort_order);
 189 #else
 190       gold_unreachable();
 191 #endif
 192     }
 193   else
 194     gold_unreachable();
 195 }
 196
 197 // Allocated the common symbols, sized version.
 198
 199 template<int size>
 200 void
 201 Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile,
 202                                   Sort_commons_order sort_order)
 203 {
 204   if (!this->commons_.empty())
 205     this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
 206                                          &this->commons_, mapfile,
 207                                          sort_order);
 208   if (!this->tls_commons_.empty())
 209     this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
 210                                          &this->tls_commons_, mapfile,
 211                                          sort_order);
 212   if (!this->small_commons_.empty())
 213     this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
 214                                          &this->small_commons_, mapfile,
 215                                          sort_order);
 216   if (!this->large_commons_.empty())
 217     this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
 218                                          &this->large_commons_, mapfile,
 219                                          sort_order);
 220 }
 221
 222 // Allocate the common symbols in a list.  IS_TLS indicates whether
 223 // these are TLS common symbols.
 224
 225 template<int size>
 226 void
 227 Symbol_table::do_allocate_commons_list(
 228     Layout* layout,
 229     Commons_section_type commons_section_type,
 230     Commons_type* commons,
 231     Mapfile* mapfile,
 232     Sort_commons_order sort_order)
 233 {
 234   typedef typename Sized_symbol<size>::Value_type Value_type;
 235   typedef typename Sized_symbol<size>::Size_type Size_type;
 236
 237   // We've kept a list of all the common symbols.  But the symbol may
 238   // have been resolved to a defined symbol by now.  And it may be a
 239   // forwarder.  First remove all non-common symbols.
 240   bool any = false;
 241   uint64_t addralign = 0;
 242   for (Commons_type::iterator p = commons->begin();
 243        p != commons->end();
 244        ++p)
 245     {
 246       Symbol* sym = *p;
 247       if (sym->is_forwarder())
 248         {
 249           sym = this->resolve_forwards(sym);
 250           *p = sym;
 251         }
 252       if (!sym->is_common())
 253         *p = NULL;
 254       else
 255         {
 256           any = true;
 257           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 258           if (ssym->value() > addralign)
 259             addralign = ssym->value();
 260         }
 261     }
 262   if (!any)
 263     return;
 264
 265   // Sort the common symbols.
 266   std::sort(commons->begin(), commons->end(),
 267             Sort_commons<size>(this, sort_order));
 268
 269   // Place them in a newly allocated BSS section.
 270   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 271   const char* name;
 272   const char* ds_name;
 273   switch (commons_section_type)
 274     {
 275     case COMMONS_NORMAL:
 276       name = ".bss";
 277       ds_name = "** common";
 278       break;
 279     case COMMONS_TLS:
 280       flags |= elfcpp::SHF_TLS;
 281       name = ".tbss";
 282       ds_name = "** tls common";
 283       break;
 284     case COMMONS_SMALL:
 285       flags |= parameters->target().small_common_section_flags();
 286       name = ".sbss";
 287       ds_name = "** small common";
 288       break;
 289     case COMMONS_LARGE:
 290       flags |= parameters->target().large_common_section_flags();
 291       name = ".lbss";
 292       ds_name = "** large common";
 293       break;
 294     default:
 295       gold_unreachable();
 296     }
 297
 298   Output_data_space *poc = new Output_data_space(addralign, ds_name);
 299   Output_section *os = layout->add_output_section_data(name,
 300                                                        elfcpp::SHT_NOBITS,
 301                                                        flags, poc,
 302                                                        ORDER_INVALID,
 303                                                        false);
 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       off = align_address(off, ssym->value());
 342       ssym->allocate_common(poc, off);
 343       off += ssym->symsize();
 344     }
 345
 346   poc->set_current_data_size(off);
 347
 348   commons->clear();
 349 }
 350
 351 } // End namespace gold.