1 // common.cc -- handle common symbols for gold 2 3 // Copyright (C) 2006-2016 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 // We've kept a list of all the common symbols. But the symbol may 226 // have been resolved to a defined symbol by now. And it may be a 227 // forwarder. First remove all non-common symbols. 228 bool any = false; 229 uint64_t addralign = 0; 230 for (Commons_type::iterator p = commons->begin(); 231 p != commons->end(); 232 ++p) 233 { 234 Symbol* sym = *p; 235 if (sym->is_forwarder()) 236 { 237 sym = this->resolve_forwards(sym); 238 *p = sym; 239 } 240 if (!sym->is_common()) 241 *p = NULL; 242 else 243 { 244 any = true; 245 Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym); 246 if (ssym->value() > addralign) 247 addralign = ssym->value(); 248 } 249 } 250 if (!any) 251 return; 252 253 // Sort the common symbols. 254 std::sort(commons->begin(), commons->end(), 255 Sort_commons<size>(this, sort_order)); 256 257 // Place them in a newly allocated BSS section. 258 elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC; 259 const char* name; 260 const char* ds_name; 261 switch (commons_section_type) 262 { 263 case COMMONS_NORMAL: 264 name = ".bss"; 265 ds_name = "** common"; 266 break; 267 case COMMONS_TLS: 268 flags |= elfcpp::SHF_TLS; 269 name = ".tbss"; 270 ds_name = "** tls common"; 271 break; 272 case COMMONS_SMALL: 273 flags |= parameters->target().small_common_section_flags(); 274 name = ".sbss"; 275 ds_name = "** small common"; 276 break; 277 case COMMONS_LARGE: 278 flags |= parameters->target().large_common_section_flags(); 279 name = ".lbss"; 280 ds_name = "** large common"; 281 break; 282 default: 283 gold_unreachable(); 284 } 285 286 Output_data_space* poc; 287 Output_section* os; 288 289 if (!parameters->incremental_update()) 290 { 291 poc = new Output_data_space(addralign, ds_name); 292 os = layout->add_output_section_data(name, elfcpp::SHT_NOBITS, flags, 293 poc, ORDER_INVALID, false); 294 } 295 else 296 { 297 // When doing an incremental update, we need to allocate each common 298 // directly from the output section's free list. 299 poc = NULL; 300 os = layout->find_output_section(name); 301 } 302 303 if (os != NULL) 304 { 305 if (commons_section_type == COMMONS_SMALL) 306 os->set_is_small_section(); 307 else if (commons_section_type == COMMONS_LARGE) 308 os->set_is_large_section(); 309 } 310 311 // Allocate them all. 312 313 off_t off = 0; 314 for (Commons_type::iterator p = commons->begin(); 315 p != commons->end(); 316 ++p) 317 { 318 Symbol* sym = *p; 319 if (sym == NULL) 320 break; 321 322 // Because we followed forwarding symbols above, but we didn't 323 // do it reliably before adding symbols to the list, it is 324 // possible for us to have the same symbol on the list twice. 325 // This can happen in the horrible case where a program defines 326 // a common symbol with the same name as a versioned libc 327 // symbol. That will show up here as a symbol which has already 328 // been allocated and is therefore no longer a common symbol. 329 if (!sym->is_common()) 330 continue; 331 332 Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym); 333 334 // Record the symbol in the map file now, before we change its 335 // value. Pass the size in separately so that we don't have to 336 // templatize the map code, which is not performance sensitive. 337 if (mapfile != NULL) 338 mapfile->report_allocate_common(sym, ssym->symsize()); 339 340 if (poc != NULL) 341 { 342 off = align_address(off, ssym->value()); 343 ssym->allocate_common(poc, off); 344 off += ssym->symsize(); 345 } 346 else 347 { 348 // For an incremental update, allocate from the free list. 349 off = os->allocate(ssym->symsize(), ssym->value()); 350 if (off == -1) 351 gold_fallback(_("out of patch space in section %s; " 352 "relink with --incremental-full"), 353 os->name()); 354 ssym->allocate_common(os, off); 355 } 356 } 357 358 if (poc != NULL) 359 poc->set_current_data_size(off); 360 361 commons->clear(); 362 } 363 364 } // End namespace gold. 365