1 // target-reloc.h -- target specific relocation support -*- C++ -*-
3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
4 // Written by Ian Lance Taylor <iant@google.com>.
6 // This file is part of gold.
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.
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.
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.
23 #ifndef GOLD_TARGET_RELOC_H
24 #define GOLD_TARGET_RELOC_H
30 #include "reloc-types.h"
35 // This function implements the generic part of reloc scanning. The
36 // template parameter Scan must be a class type which provides two
37 // functions: local() and global(). Those functions implement the
38 // machine specific part of scanning. We do it this way to
39 // avoidmaking a function call for each relocation, and to avoid
40 // repeating the generic code for each target.
42 template<int size, bool big_endian, typename Target_type, int sh_type,
46 const General_options& options,
50 Sized_relobj<size, big_endian>* object,
51 unsigned int data_shndx,
52 const unsigned char* prelocs,
54 Output_section* output_section,
55 bool needs_special_offset_handling,
57 const unsigned char* plocal_syms)
59 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
60 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
61 const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
64 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
66 Reltype reloc(prelocs);
68 if (needs_special_offset_handling
69 && !output_section->is_input_address_mapped(object, data_shndx,
70 reloc.get_r_offset()))
73 typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
74 unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
75 unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
77 if (r_sym < local_count)
79 gold_assert(plocal_syms != NULL);
80 typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
82 unsigned int shndx = lsym.get_st_shndx();
84 shndx = object->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
86 && shndx != elfcpp::SHN_UNDEF
87 && !object->is_section_included(shndx))
89 // RELOC is a relocation against a local symbol in a
90 // section we are discarding. We can ignore this
91 // relocation. It will eventually become a reloc
92 // against the value zero.
94 // FIXME: We should issue a warning if this is an
95 // allocated section; is this the best place to do it?
97 // FIXME: The old GNU linker would in some cases look
98 // for the linkonce section which caused this section to
99 // be discarded, and, if the other section was the same
100 // size, change the reloc to refer to the other section.
101 // That seems risky and weird to me, and I don't know of
102 // any case where it is actually required.
107 scan.local(options, symtab, layout, target, object, data_shndx,
108 output_section, reloc, r_type, lsym);
112 Symbol* gsym = object->global_symbol(r_sym);
113 gold_assert(gsym != NULL);
114 if (gsym->is_forwarder())
115 gsym = symtab->resolve_forwards(gsym);
117 scan.global(options, symtab, layout, target, object, data_shndx,
118 output_section, reloc, r_type, gsym);
123 // Behavior for relocations to discarded comdat sections.
127 CB_UNDETERMINED, // Not yet determined -- need to look at section name.
128 CB_PRETEND, // Attempt to map to the corresponding kept section.
129 CB_IGNORE, // Ignore the relocation.
130 CB_WARNING // Print a warning.
133 // Decide what the linker should do for relocations that refer to discarded
134 // comdat sections. This decision is based on the name of the section being
137 inline Comdat_behavior
138 get_comdat_behavior(const char* name)
140 if (Layout::is_debug_info_section(name))
142 if (strcmp(name, ".eh_frame") == 0
143 || strcmp(name, ".gcc_except_table") == 0)
148 // This function implements the generic part of relocation processing.
149 // The template parameter Relocate must be a class type which provides
150 // a single function, relocate(), which implements the machine
151 // specific part of a relocation.
153 // SIZE is the ELF size: 32 or 64. BIG_ENDIAN is the endianness of
154 // the data. SH_TYPE is the section type: SHT_REL or SHT_RELA.
155 // RELOCATE implements operator() to do a relocation.
157 // PRELOCS points to the relocation data. RELOC_COUNT is the number
158 // of relocs. OUTPUT_SECTION is the output section.
159 // NEEDS_SPECIAL_OFFSET_HANDLING is true if input offsets need to be
160 // mapped to output offsets.
162 // VIEW is the section data, VIEW_ADDRESS is its memory address, and
163 // VIEW_SIZE is the size. These refer to the input section, unless
164 // NEEDS_SPECIAL_OFFSET_HANDLING is true, in which case they refer to
165 // the output section.
167 // RELOC_SYMBOL_CHANGES is used for -fsplit-stack support. If it is
168 // not NULL, it is a vector indexed by relocation index. If that
169 // entry is not NULL, it points to a global symbol which used as the
170 // symbol for the relocation, ignoring the symbol index in the
173 template<int size, bool big_endian, typename Target_type, int sh_type,
177 const Relocate_info<size, big_endian>* relinfo,
179 const unsigned char* prelocs,
181 Output_section* output_section,
182 bool needs_special_offset_handling,
184 typename elfcpp::Elf_types<size>::Elf_Addr view_address,
185 section_size_type view_size,
186 const Reloc_symbol_changes* reloc_symbol_changes)
188 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
189 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
192 Sized_relobj<size, big_endian>* object = relinfo->object;
193 unsigned int local_count = object->local_symbol_count();
195 Comdat_behavior comdat_behavior = CB_UNDETERMINED;
197 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
199 Reltype reloc(prelocs);
201 section_offset_type offset =
202 convert_to_section_size_type(reloc.get_r_offset());
204 if (needs_special_offset_handling)
206 offset = output_section->output_offset(relinfo->object,
213 typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
214 unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
215 unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
217 const Sized_symbol<size>* sym;
219 Symbol_value<size> symval;
220 const Symbol_value<size> *psymval;
221 if (r_sym < local_count
222 && (reloc_symbol_changes == NULL
223 || (*reloc_symbol_changes)[i] == NULL))
226 psymval = object->local_symbol(r_sym);
228 // If the local symbol belongs to a section we are discarding,
229 // and that section is a debug section, try to find the
230 // corresponding kept section and map this symbol to its
231 // counterpart in the kept section. The symbol must not
232 // correspond to a section we are folding.
234 unsigned int shndx = psymval->input_shndx(&is_ordinary);
236 && shndx != elfcpp::SHN_UNDEF
237 && !object->is_section_included(shndx)
238 && !(relinfo->symtab->is_section_folded(object, shndx)))
240 if (comdat_behavior == CB_UNDETERMINED)
242 std::string name = object->section_name(relinfo->data_shndx);
243 comdat_behavior = get_comdat_behavior(name.c_str());
245 if (comdat_behavior == CB_PRETEND)
248 typename elfcpp::Elf_types<size>::Elf_Addr value =
249 object->map_to_kept_section(shndx, &found);
251 symval.set_output_value(value + psymval->input_value());
253 symval.set_output_value(0);
257 if (comdat_behavior == CB_WARNING)
258 gold_warning_at_location(relinfo, i, offset,
259 _("relocation refers to discarded "
261 symval.set_output_value(0);
263 symval.set_no_output_symtab_entry();
270 if (reloc_symbol_changes != NULL
271 && (*reloc_symbol_changes)[i] != NULL)
272 gsym = (*reloc_symbol_changes)[i];
275 gsym = object->global_symbol(r_sym);
276 gold_assert(gsym != NULL);
277 if (gsym->is_forwarder())
278 gsym = relinfo->symtab->resolve_forwards(gsym);
281 sym = static_cast<const Sized_symbol<size>*>(gsym);
282 if (sym->has_symtab_index())
283 symval.set_output_symtab_index(sym->symtab_index());
285 symval.set_no_output_symtab_entry();
286 symval.set_output_value(sym->value());
290 if (!relocate.relocate(relinfo, target, output_section, i, reloc,
291 r_type, sym, psymval, view + offset,
292 view_address + offset, view_size))
295 if (offset < 0 || static_cast<section_size_type>(offset) >= view_size)
297 gold_error_at_location(relinfo, i, offset,
298 _("reloc has bad offset %zu"),
299 static_cast<size_t>(offset));
304 && sym->is_undefined()
305 && sym->binding() != elfcpp::STB_WEAK
306 && !target->is_defined_by_abi(sym)
307 && (!parameters->options().shared() // -shared
308 || parameters->options().defs())) // -z defs
309 gold_undefined_symbol_at_location(sym, relinfo, i, offset);
311 if (sym != NULL && sym->has_warning())
312 relinfo->symtab->issue_warning(sym, relinfo, i, offset);
316 // This class may be used as a typical class for the
317 // Scan_relocatable_reloc parameter to scan_relocatable_relocs. The
318 // template parameter Classify_reloc must be a class type which
319 // provides a function get_size_for_reloc which returns the number of
320 // bytes to which a reloc applies. This class is intended to capture
321 // the most typical target behaviour, while still permitting targets
322 // to define their own independent class for Scan_relocatable_reloc.
324 template<int sh_type, typename Classify_reloc>
325 class Default_scan_relocatable_relocs
328 // Return the strategy to use for a local symbol which is not a
329 // section symbol, given the relocation type.
330 inline Relocatable_relocs::Reloc_strategy
331 local_non_section_strategy(unsigned int r_type, Relobj*, unsigned int r_sym)
333 // We assume that relocation type 0 is NONE. Targets which are
334 // different must override.
335 if (r_type == 0 && r_sym == 0)
336 return Relocatable_relocs::RELOC_DISCARD;
337 return Relocatable_relocs::RELOC_COPY;
340 // Return the strategy to use for a local symbol which is a section
341 // symbol, given the relocation type.
342 inline Relocatable_relocs::Reloc_strategy
343 local_section_strategy(unsigned int r_type, Relobj* object)
345 if (sh_type == elfcpp::SHT_RELA)
346 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA;
349 Classify_reloc classify;
350 switch (classify.get_size_for_reloc(r_type, object))
353 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0;
355 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1;
357 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2;
359 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4;
361 return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8;
368 // Return the strategy to use for a global symbol, given the
369 // relocation type, the object, and the symbol index.
370 inline Relocatable_relocs::Reloc_strategy
371 global_strategy(unsigned int, Relobj*, unsigned int)
372 { return Relocatable_relocs::RELOC_COPY; }
375 // Scan relocs during a relocatable link. This is a default
376 // definition which should work for most targets.
377 // Scan_relocatable_reloc must name a class type which provides three
378 // functions which return a Relocatable_relocs::Reloc_strategy code:
379 // global_strategy, local_non_section_strategy, and
380 // local_section_strategy. Most targets should be able to use
381 // Default_scan_relocatable_relocs as this class.
383 template<int size, bool big_endian, int sh_type,
384 typename Scan_relocatable_reloc>
386 scan_relocatable_relocs(
387 const General_options&,
390 Sized_relobj<size, big_endian>* object,
391 unsigned int data_shndx,
392 const unsigned char* prelocs,
394 Output_section* output_section,
395 bool needs_special_offset_handling,
396 size_t local_symbol_count,
397 const unsigned char* plocal_syms,
398 Relocatable_relocs* rr)
400 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
401 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
402 const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
403 Scan_relocatable_reloc scan;
405 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
407 Reltype reloc(prelocs);
409 Relocatable_relocs::Reloc_strategy strategy;
411 if (needs_special_offset_handling
412 && !output_section->is_input_address_mapped(object, data_shndx,
413 reloc.get_r_offset()))
414 strategy = Relocatable_relocs::RELOC_DISCARD;
417 typename elfcpp::Elf_types<size>::Elf_WXword r_info =
419 const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
420 const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
422 if (r_sym >= local_symbol_count)
423 strategy = scan.global_strategy(r_type, object, r_sym);
426 gold_assert(plocal_syms != NULL);
427 typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
429 unsigned int shndx = lsym.get_st_shndx();
431 shndx = object->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
433 && shndx != elfcpp::SHN_UNDEF
434 && !object->is_section_included(shndx))
436 // RELOC is a relocation against a local symbol
437 // defined in a section we are discarding. Discard
438 // the reloc. FIXME: Should we issue a warning?
439 strategy = Relocatable_relocs::RELOC_DISCARD;
441 else if (lsym.get_st_type() != elfcpp::STT_SECTION)
442 strategy = scan.local_non_section_strategy(r_type, object,
446 strategy = scan.local_section_strategy(r_type, object);
447 if (strategy != Relocatable_relocs::RELOC_DISCARD)
448 object->output_section(shndx)->set_needs_symtab_index();
453 rr->set_next_reloc_strategy(strategy);
457 // Relocate relocs during a relocatable link. This is a default
458 // definition which should work for most targets.
460 template<int size, bool big_endian, int sh_type>
462 relocate_for_relocatable(
463 const Relocate_info<size, big_endian>* relinfo,
464 const unsigned char* prelocs,
466 Output_section* output_section,
467 typename elfcpp::Elf_types<size>::Elf_Addr offset_in_output_section,
468 const Relocatable_relocs* rr,
470 typename elfcpp::Elf_types<size>::Elf_Addr view_address,
472 unsigned char* reloc_view,
473 section_size_type reloc_view_size)
475 typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
476 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
477 typedef typename Reloc_types<sh_type, size, big_endian>::Reloc_write
479 const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
480 const Address invalid_address = static_cast<Address>(0) - 1;
482 Sized_relobj<size, big_endian>* const object = relinfo->object;
483 const unsigned int local_count = object->local_symbol_count();
485 unsigned char* pwrite = reloc_view;
487 for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
489 Relocatable_relocs::Reloc_strategy strategy = rr->strategy(i);
490 if (strategy == Relocatable_relocs::RELOC_DISCARD)
493 Reltype reloc(prelocs);
494 Reltype_write reloc_write(pwrite);
496 typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
497 const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
498 const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
500 // Get the new symbol index.
502 unsigned int new_symndx;
503 if (r_sym < local_count)
507 case Relocatable_relocs::RELOC_COPY:
508 new_symndx = object->symtab_index(r_sym);
509 gold_assert(new_symndx != -1U);
512 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
513 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
514 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
515 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
516 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
517 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
519 // We are adjusting a section symbol. We need to find
520 // the symbol table index of the section symbol for
521 // the output section corresponding to input section
522 // in which this symbol is defined.
523 gold_assert(r_sym < local_count);
526 object->local_symbol_input_shndx(r_sym, &is_ordinary);
527 gold_assert(is_ordinary);
528 Output_section* os = object->output_section(shndx);
529 gold_assert(os != NULL);
530 gold_assert(os->needs_symtab_index());
531 new_symndx = os->symtab_index();
541 const Symbol* gsym = object->global_symbol(r_sym);
542 gold_assert(gsym != NULL);
543 if (gsym->is_forwarder())
544 gsym = relinfo->symtab->resolve_forwards(gsym);
546 gold_assert(gsym->has_symtab_index());
547 new_symndx = gsym->symtab_index();
550 // Get the new offset--the location in the output section where
551 // this relocation should be applied.
553 Address offset = reloc.get_r_offset();
555 if (offset_in_output_section != invalid_address)
556 new_offset = offset + offset_in_output_section;
559 section_offset_type sot_offset =
560 convert_types<section_offset_type, Address>(offset);
561 section_offset_type new_sot_offset =
562 output_section->output_offset(object, relinfo->data_shndx,
564 gold_assert(new_sot_offset != -1);
565 new_offset = new_sot_offset;
568 // In an object file, r_offset is an offset within the section.
569 // In an executable or dynamic object, generated by
570 // --emit-relocs, r_offset is an absolute address.
571 if (!parameters->options().relocatable())
573 new_offset += view_address;
574 if (offset_in_output_section != invalid_address)
575 new_offset -= offset_in_output_section;
578 reloc_write.put_r_offset(new_offset);
579 reloc_write.put_r_info(elfcpp::elf_r_info<size>(new_symndx, r_type));
581 // Handle the reloc addend based on the strategy.
583 if (strategy == Relocatable_relocs::RELOC_COPY)
585 if (sh_type == elfcpp::SHT_RELA)
586 Reloc_types<sh_type, size, big_endian>::
587 copy_reloc_addend(&reloc_write,
592 // The relocation uses a section symbol in the input file.
593 // We are adjusting it to use a section symbol in the output
594 // file. The input section symbol refers to some address in
595 // the input section. We need the relocation in the output
596 // file to refer to that same address. This adjustment to
597 // the addend is the same calculation we use for a simple
598 // absolute relocation for the input section symbol.
600 const Symbol_value<size>* psymval = object->local_symbol(r_sym);
602 unsigned char* padd = view + offset;
605 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
607 typename elfcpp::Elf_types<size>::Elf_Swxword addend;
608 addend = Reloc_types<sh_type, size, big_endian>::
609 get_reloc_addend(&reloc);
610 addend = psymval->value(object, addend);
611 Reloc_types<sh_type, size, big_endian>::
612 set_reloc_addend(&reloc_write, addend);
616 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
619 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
620 Relocate_functions<size, big_endian>::rel8(padd, object,
624 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
625 Relocate_functions<size, big_endian>::rel16(padd, object,
629 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
630 Relocate_functions<size, big_endian>::rel32(padd, object,
634 case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
635 Relocate_functions<size, big_endian>::rel64(padd, object,
644 pwrite += reloc_size;
647 gold_assert(static_cast<section_size_type>(pwrite - reloc_view)
651 } // End namespace gold.
653 #endif // !defined(GOLD_TARGET_RELOC_H)