1 // target.h -- target support for gold -*- C++ -*-
3 // Copyright 2006, 2007, 2008, 2009 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 // The abstract class Target is the interface for target specific
24 // support. It defines abstract methods which each target must
25 // implement. Typically there will be one target per processor, but
26 // in some cases it may be necessary to have subclasses.
28 // For speed and consistency we want to use inline functions to handle
29 // relocation processing. So besides implementations of the abstract
30 // methods, each target is expected to define a template
31 // specialization of the relocation functions.
38 #include "parameters.h"
46 template<int size, bool big_endian>
48 class Relocatable_relocs;
49 template<int size, bool big_endian>
51 class Reloc_symbol_changes;
59 // The abstract class for target specific handling.
67 // Virtual function which is set to return true by a target if
68 // it can use relocation types to determine if a function's
71 can_check_for_function_pointers() const
74 // Return the bit size that this target implements. This should
78 { return this->pti_->size; }
80 // Return whether this target is big-endian.
83 { return this->pti_->is_big_endian; }
85 // Machine code to store in e_machine field of ELF header.
88 { return this->pti_->machine_code; }
90 // Processor specific flags to store in e_flags field of ELF header.
92 processor_specific_flags() const
93 { return this->processor_specific_flags_; }
95 // Whether processor specific flags are set at least once.
97 are_processor_specific_flags_set() const
98 { return this->are_processor_specific_flags_set_; }
100 // Whether this target has a specific make_symbol function.
102 has_make_symbol() const
103 { return this->pti_->has_make_symbol; }
105 // Whether this target has a specific resolve function.
108 { return this->pti_->has_resolve; }
110 // Whether this target has a specific code fill function.
112 has_code_fill() const
113 { return this->pti_->has_code_fill; }
115 // Return the default name of the dynamic linker.
117 dynamic_linker() const
118 { return this->pti_->dynamic_linker; }
120 // Return the default address to use for the text segment.
122 default_text_segment_address() const
123 { return this->pti_->default_text_segment_address; }
125 // Return the ABI specified page size.
129 if (parameters->options().max_page_size() > 0)
130 return parameters->options().max_page_size();
132 return this->pti_->abi_pagesize;
135 // Return the common page size used on actual systems.
137 common_pagesize() const
139 if (parameters->options().common_page_size() > 0)
140 return std::min(parameters->options().common_page_size(),
141 this->abi_pagesize());
143 return std::min(this->pti_->common_pagesize,
144 this->abi_pagesize());
147 // If we see some object files with .note.GNU-stack sections, and
148 // some objects files without them, this returns whether we should
149 // consider the object files without them to imply that the stack
150 // should be executable.
152 is_default_stack_executable() const
153 { return this->pti_->is_default_stack_executable; }
155 // Return a character which may appear as a prefix for a wrap
156 // symbol. If this character appears, we strip it when checking for
157 // wrapping and add it back when forming the final symbol name.
158 // This should be '\0' if not special prefix is required, which is
162 { return this->pti_->wrap_char; }
164 // Return the special section index which indicates a small common
165 // symbol. This will return SHN_UNDEF if there are no small common
168 small_common_shndx() const
169 { return this->pti_->small_common_shndx; }
171 // Return values to add to the section flags for the section holding
172 // small common symbols.
174 small_common_section_flags() const
176 gold_assert(this->pti_->small_common_shndx != elfcpp::SHN_UNDEF);
177 return this->pti_->small_common_section_flags;
180 // Return the special section index which indicates a large common
181 // symbol. This will return SHN_UNDEF if there are no large common
184 large_common_shndx() const
185 { return this->pti_->large_common_shndx; }
187 // Return values to add to the section flags for the section holding
188 // large common symbols.
190 large_common_section_flags() const
192 gold_assert(this->pti_->large_common_shndx != elfcpp::SHN_UNDEF);
193 return this->pti_->large_common_section_flags;
196 // This hook is called when an output section is created.
198 new_output_section(Output_section* os) const
199 { this->do_new_output_section(os); }
201 // This is called to tell the target to complete any sections it is
202 // handling. After this all sections must have their final size.
204 finalize_sections(Layout* layout, const Input_objects* input_objects,
205 Symbol_table* symtab)
206 { return this->do_finalize_sections(layout, input_objects, symtab); }
208 // Return the value to use for a global symbol which needs a special
209 // value in the dynamic symbol table. This will only be called if
210 // the backend first calls symbol->set_needs_dynsym_value().
212 dynsym_value(const Symbol* sym) const
213 { return this->do_dynsym_value(sym); }
215 // Return a string to use to fill out a code section. This is
216 // basically one or more NOPS which must fill out the specified
219 code_fill(section_size_type length) const
220 { return this->do_code_fill(length); }
222 // Return whether SYM is known to be defined by the ABI. This is
223 // used to avoid inappropriate warnings about undefined symbols.
225 is_defined_by_abi(const Symbol* sym) const
226 { return this->do_is_defined_by_abi(sym); }
228 // Adjust the output file header before it is written out. VIEW
229 // points to the header in external form. LEN is the length.
231 adjust_elf_header(unsigned char* view, int len) const
232 { return this->do_adjust_elf_header(view, len); }
234 // Return whether NAME is a local label name. This is used to implement the
235 // --discard-locals options.
237 is_local_label_name(const char* name) const
238 { return this->do_is_local_label_name(name); }
240 // Get the symbol index to use for a target specific reloc.
242 reloc_symbol_index(void* arg, unsigned int type) const
243 { return this->do_reloc_symbol_index(arg, type); }
245 // Get the addend to use for a target specific reloc.
247 reloc_addend(void* arg, unsigned int type, uint64_t addend) const
248 { return this->do_reloc_addend(arg, type, addend); }
250 // A function starts at OFFSET in section SHNDX in OBJECT. That
251 // function was compiled with -fsplit-stack, but it refers to a
252 // function which was compiled without -fsplit-stack. VIEW is a
253 // modifiable view of the section; VIEW_SIZE is the size of the
254 // view. The target has to adjust the function so that it allocates
257 calls_non_split(Relobj* object, unsigned int shndx,
258 section_offset_type fnoffset, section_size_type fnsize,
259 unsigned char* view, section_size_type view_size,
260 std::string* from, std::string* to) const
262 this->do_calls_non_split(object, shndx, fnoffset, fnsize, view, view_size,
266 // Make an ELF object.
267 template<int size, bool big_endian>
269 make_elf_object(const std::string& name, Input_file* input_file,
270 off_t offset, const elfcpp::Ehdr<size, big_endian>& ehdr)
271 { return this->do_make_elf_object(name, input_file, offset, ehdr); }
273 // Make an output section.
275 make_output_section(const char* name, elfcpp::Elf_Word type,
276 elfcpp::Elf_Xword flags)
277 { return this->do_make_output_section(name, type, flags); }
279 // Return true if target wants to perform relaxation.
283 // Run the dummy relaxation pass twice if relaxation debugging is enabled.
284 if (is_debugging_enabled(DEBUG_RELAXATION))
287 return this->do_may_relax();
290 // Perform a relaxation pass. Return true if layout may be changed.
292 relax(int pass, const Input_objects* input_objects, Symbol_table* symtab,
295 // Run the dummy relaxation pass twice if relaxation debugging is enabled.
296 if (is_debugging_enabled(DEBUG_RELAXATION))
299 return this->do_relax(pass, input_objects, symtab, layout);
302 // Return the target-specific name of attributes section. This is
303 // NULL if a target does not use attributes section or if it uses
304 // the default section name ".gnu.attributes".
306 attributes_section() const
307 { return this->pti_->attributes_section; }
309 // Return the vendor name of vendor attributes.
311 attributes_vendor() const
312 { return this->pti_->attributes_vendor; }
314 // Whether a section called NAME is an attribute section.
316 is_attributes_section(const char* name) const
318 return ((this->pti_->attributes_section != NULL
319 && strcmp(name, this->pti_->attributes_section) == 0)
320 || strcmp(name, ".gnu.attributes") == 0);
323 // Return a bit mask of argument types for attribute with TAG.
325 attribute_arg_type(int tag) const
326 { return this->do_attribute_arg_type(tag); }
328 // Return the attribute tag of the position NUM in the list of fixed
329 // attributes. Normally there is no reordering and
330 // attributes_order(NUM) == NUM.
332 attributes_order(int num) const
333 { return this->do_attributes_order(num); }
335 // When a target is selected as the default target, we call this method,
336 // which may be used for expensive, target-specific initialization.
338 select_as_default_target()
339 { this->do_select_as_default_target(); }
342 // This struct holds the constant information for a child class. We
343 // use a struct to avoid the overhead of virtual function calls for
344 // simple information.
347 // Address size (32 or 64).
349 // Whether the target is big endian.
351 // The code to store in the e_machine field of the ELF header.
352 elfcpp::EM machine_code;
353 // Whether this target has a specific make_symbol function.
354 bool has_make_symbol;
355 // Whether this target has a specific resolve function.
357 // Whether this target has a specific code fill function.
359 // Whether an object file with no .note.GNU-stack sections implies
360 // that the stack should be executable.
361 bool is_default_stack_executable;
362 // Prefix character to strip when checking for wrapping.
364 // The default dynamic linker name.
365 const char* dynamic_linker;
366 // The default text segment address.
367 uint64_t default_text_segment_address;
368 // The ABI specified page size.
369 uint64_t abi_pagesize;
370 // The common page size used by actual implementations.
371 uint64_t common_pagesize;
372 // The special section index for small common symbols; SHN_UNDEF
374 elfcpp::Elf_Half small_common_shndx;
375 // The special section index for large common symbols; SHN_UNDEF
377 elfcpp::Elf_Half large_common_shndx;
378 // Section flags for small common section.
379 elfcpp::Elf_Xword small_common_section_flags;
380 // Section flags for large common section.
381 elfcpp::Elf_Xword large_common_section_flags;
382 // Name of attributes section if it is not ".gnu.attributes".
383 const char* attributes_section;
384 // Vendor name of vendor attributes.
385 const char* attributes_vendor;
388 Target(const Target_info* pti)
389 : pti_(pti), processor_specific_flags_(0),
390 are_processor_specific_flags_set_(false)
393 // Virtual function which may be implemented by the child class.
395 do_new_output_section(Output_section*) const
398 // Virtual function which may be implemented by the child class.
400 do_finalize_sections(Layout*, const Input_objects*, Symbol_table*)
403 // Virtual function which may be implemented by the child class.
405 do_dynsym_value(const Symbol*) const
406 { gold_unreachable(); }
408 // Virtual function which must be implemented by the child class if
411 do_code_fill(section_size_type) const
412 { gold_unreachable(); }
414 // Virtual function which may be implemented by the child class.
416 do_is_defined_by_abi(const Symbol*) const
419 // Adjust the output file header before it is written out. VIEW
420 // points to the header in external form. LEN is the length, and
421 // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.
422 // By default, we do nothing.
424 do_adjust_elf_header(unsigned char*, int) const
427 // Virtual function which may be overriden by the child class.
429 do_is_local_label_name(const char*) const;
431 // Virtual function that must be overridden by a target which uses
432 // target specific relocations.
434 do_reloc_symbol_index(void*, unsigned int) const
435 { gold_unreachable(); }
437 // Virtual function that must be overidden by a target which uses
438 // target specific relocations.
440 do_reloc_addend(void*, unsigned int, uint64_t) const
441 { gold_unreachable(); }
443 // Virtual function which may be overridden by the child class.
445 do_calls_non_split(Relobj* object, unsigned int, section_offset_type,
446 section_size_type, unsigned char*, section_size_type,
447 std::string*, std::string*) const;
449 // make_elf_object hooks. There are four versions of these for
450 // different address sizes and endianities.
452 // Set processor specific flags.
454 set_processor_specific_flags(elfcpp::Elf_Word flags)
456 this->processor_specific_flags_ = flags;
457 this->are_processor_specific_flags_set_ = true;
460 #ifdef HAVE_TARGET_32_LITTLE
461 // Virtual functions which may be overriden by the child class.
463 do_make_elf_object(const std::string&, Input_file*, off_t,
464 const elfcpp::Ehdr<32, false>&);
467 #ifdef HAVE_TARGET_32_BIG
468 // Virtual functions which may be overriden by the child class.
470 do_make_elf_object(const std::string&, Input_file*, off_t,
471 const elfcpp::Ehdr<32, true>&);
474 #ifdef HAVE_TARGET_64_LITTLE
475 // Virtual functions which may be overriden by the child class.
477 do_make_elf_object(const std::string&, Input_file*, off_t,
478 const elfcpp::Ehdr<64, false>& ehdr);
481 #ifdef HAVE_TARGET_64_BIG
482 // Virtual functions which may be overriden by the child class.
484 do_make_elf_object(const std::string& name, Input_file* input_file,
485 off_t offset, const elfcpp::Ehdr<64, true>& ehdr);
488 // Virtual functions which may be overriden by the child class.
489 virtual Output_section*
490 do_make_output_section(const char* name, elfcpp::Elf_Word type,
491 elfcpp::Elf_Xword flags);
493 // Virtual function which may be overriden by the child class.
496 { return parameters->options().relax(); }
498 // Virtual function which may be overriden by the child class.
500 do_relax(int, const Input_objects*, Symbol_table*, Layout*)
503 // A function for targets to call. Return whether BYTES/LEN matches
504 // VIEW/VIEW_SIZE at OFFSET.
506 match_view(const unsigned char* view, section_size_type view_size,
507 section_offset_type offset, const char* bytes, size_t len) const;
509 // Set the contents of a VIEW/VIEW_SIZE to nops starting at OFFSET
512 set_view_to_nop(unsigned char* view, section_size_type view_size,
513 section_offset_type offset, size_t len) const;
515 // This must be overriden by the child class if it has target-specific
516 // attributes subsection in the attribute section.
518 do_attribute_arg_type(int) const
519 { gold_unreachable(); }
521 // This may be overridden by the child class.
523 do_attributes_order(int num) const
526 // This may be overridden by the child class.
528 do_select_as_default_target()
532 // The implementations of the four do_make_elf_object virtual functions are
533 // almost identical except for their sizes and endianity. We use a template.
534 // for their implementations.
535 template<int size, bool big_endian>
537 do_make_elf_object_implementation(const std::string&, Input_file*, off_t,
538 const elfcpp::Ehdr<size, big_endian>&);
540 Target(const Target&);
541 Target& operator=(const Target&);
543 // The target information.
544 const Target_info* pti_;
545 // Processor-specific flags.
546 elfcpp::Elf_Word processor_specific_flags_;
547 // Whether the processor-specific flags are set at least once.
548 bool are_processor_specific_flags_set_;
551 // The abstract class for a specific size and endianness of target.
552 // Each actual target implementation class should derive from an
553 // instantiation of Sized_target.
555 template<int size, bool big_endian>
556 class Sized_target : public Target
559 // Make a new symbol table entry for the target. This should be
560 // overridden by a target which needs additional information in the
561 // symbol table. This will only be called if has_make_symbol()
563 virtual Sized_symbol<size>*
565 { gold_unreachable(); }
567 // Resolve a symbol for the target. This should be overridden by a
568 // target which needs to take special action. TO is the
569 // pre-existing symbol. SYM is the new symbol, seen in OBJECT.
570 // VERSION is the version of SYM. This will only be called if
571 // has_resolve() returns true.
573 resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
575 { gold_unreachable(); }
577 // Process the relocs for a section, and record information of the
578 // mapping from source to destination sections. This mapping is later
579 // used to determine unreferenced garbage sections. This procedure is
580 // only called during garbage collection.
582 gc_process_relocs(Symbol_table* symtab,
584 Sized_relobj<size, big_endian>* object,
585 unsigned int data_shndx,
586 unsigned int sh_type,
587 const unsigned char* prelocs,
589 Output_section* output_section,
590 bool needs_special_offset_handling,
591 size_t local_symbol_count,
592 const unsigned char* plocal_symbols) = 0;
594 // Scan the relocs for a section, and record any information
595 // required for the symbol. SYMTAB is the symbol table. OBJECT is
596 // the object in which the section appears. DATA_SHNDX is the
597 // section index that these relocs apply to. SH_TYPE is the type of
598 // the relocation section, SHT_REL or SHT_RELA. PRELOCS points to
599 // the relocation data. RELOC_COUNT is the number of relocs.
600 // LOCAL_SYMBOL_COUNT is the number of local symbols.
601 // OUTPUT_SECTION is the output section.
602 // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
603 // sections are not mapped as usual. PLOCAL_SYMBOLS points to the
604 // local symbol data from OBJECT. GLOBAL_SYMBOLS is the array of
605 // pointers to the global symbol table from OBJECT.
607 scan_relocs(Symbol_table* symtab,
609 Sized_relobj<size, big_endian>* object,
610 unsigned int data_shndx,
611 unsigned int sh_type,
612 const unsigned char* prelocs,
614 Output_section* output_section,
615 bool needs_special_offset_handling,
616 size_t local_symbol_count,
617 const unsigned char* plocal_symbols) = 0;
619 // Relocate section data. SH_TYPE is the type of the relocation
620 // section, SHT_REL or SHT_RELA. PRELOCS points to the relocation
621 // information. RELOC_COUNT is the number of relocs.
622 // OUTPUT_SECTION is the output section.
623 // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
624 // to correspond to the output section. VIEW is a view into the
625 // output file holding the section contents, VIEW_ADDRESS is the
626 // virtual address of the view, and VIEW_SIZE is the size of the
627 // view. If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
628 // parameters refer to the complete output section data, not just
629 // the input section data.
631 relocate_section(const Relocate_info<size, big_endian>*,
632 unsigned int sh_type,
633 const unsigned char* prelocs,
635 Output_section* output_section,
636 bool needs_special_offset_handling,
638 typename elfcpp::Elf_types<size>::Elf_Addr view_address,
639 section_size_type view_size,
640 const Reloc_symbol_changes*) = 0;
642 // Scan the relocs during a relocatable link. The parameters are
643 // like scan_relocs, with an additional Relocatable_relocs
644 // parameter, used to record the disposition of the relocs.
646 scan_relocatable_relocs(Symbol_table* symtab,
648 Sized_relobj<size, big_endian>* object,
649 unsigned int data_shndx,
650 unsigned int sh_type,
651 const unsigned char* prelocs,
653 Output_section* output_section,
654 bool needs_special_offset_handling,
655 size_t local_symbol_count,
656 const unsigned char* plocal_symbols,
657 Relocatable_relocs*) = 0;
659 // Relocate a section during a relocatable link. The parameters are
660 // like relocate_section, with additional parameters for the view of
661 // the output reloc section.
663 relocate_for_relocatable(const Relocate_info<size, big_endian>*,
664 unsigned int sh_type,
665 const unsigned char* prelocs,
667 Output_section* output_section,
668 off_t offset_in_output_section,
669 const Relocatable_relocs*,
671 typename elfcpp::Elf_types<size>::Elf_Addr
673 section_size_type view_size,
674 unsigned char* reloc_view,
675 section_size_type reloc_view_size) = 0;
678 Sized_target(const Target::Target_info* pti)
681 gold_assert(pti->size == size);
682 gold_assert(pti->is_big_endian ? big_endian : !big_endian);
686 } // End namespace gold.
688 #endif // !defined(GOLD_TARGET_H)