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   this->do_allocate_commons_list<size>(layout, false, &this->commons_,
 150                                        mapfile);
 151   this->do_allocate_commons_list<size>(layout, true, &this->tls_commons_,
 152                                        mapfile);
 153 }
 154
 155 // Allocate the common symbols in a list.  IS_TLS indicates whether
 156 // these are TLS common symbols.
 157
 158 template<int size>
 159 void
 160 Symbol_table::do_allocate_commons_list(Layout* layout, bool is_tls,
 161                                        Commons_type* commons,
 162                                        Mapfile* mapfile)
 163 {
 164   typedef typename Sized_symbol<size>::Value_type Value_type;
 165   typedef typename Sized_symbol<size>::Size_type Size_type;
 166
 167   // We've kept a list of all the common symbols.  But the symbol may
 168   // have been resolved to a defined symbol by now.  And it may be a
 169   // forwarder.  First remove all non-common symbols.
 170   bool any = false;
 171   uint64_t addralign = 0;
 172   for (Commons_type::iterator p = commons->begin();
 173        p != commons->end();
 174        ++p)
 175     {
 176       Symbol* sym = *p;
 177       if (sym->is_forwarder())
 178         {
 179           sym = this->resolve_forwards(sym);
 180           *p = sym;
 181         }
 182       if (!sym->is_common())
 183         *p = NULL;
 184       else
 185         {
 186           any = true;
 187           Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 188           if (ssym->value() > addralign)
 189             addralign = ssym->value();
 190         }
 191     }
 192   if (!any)
 193     return;
 194
 195   // Sort the common symbols by size, so that they pack better into
 196   // memory.
 197   std::sort(commons->begin(), commons->end(),
 198             Sort_commons<size>(this));
 199
 200   // Place them in a newly allocated BSS section.
 201
 202   Output_data_space *poc = new Output_data_space(addralign,
 203                                                  (is_tls
 204                                                   ? "** tls common"
 205                                                   : "** common"));
 206
 207   const char* name = ".bss";
 208   elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
 209   if (is_tls)
 210     {
 211       name = ".tbss";
 212       flags |= elfcpp::SHF_TLS;
 213     }
 214   layout->add_output_section_data(name, elfcpp::SHT_NOBITS, flags, poc);
 215
 216   // Allocate them all.
 217
 218   off_t off = 0;
 219   for (Commons_type::iterator p = commons->begin();
 220        p != commons->end();
 221        ++p)
 222     {
 223       Symbol* sym = *p;
 224       if (sym == NULL)
 225         break;
 226       Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
 227
 228       // Record the symbol in the map file now, before we change its
 229       // value.  Pass the size in separately so that we don't have to
 230       // templatize the map code, which is not performance sensitive.
 231       if (mapfile != NULL)
 232         mapfile->report_allocate_common(sym, ssym->symsize());
 233
 234       off = align_address(off, ssym->value());
 235       ssym->allocate_common(poc, off);
 236       off += ssym->symsize();
 237     }
 238
 239   poc->set_current_data_size(off);
 240
 241   commons->clear();
 242 }
 243
 244 } // End namespace gold.