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"
43 class General_options;
45 template<int size, bool big_endian>
47 class Relocatable_relocs;
48 template<int size, bool big_endian>
56 // The abstract class for target specific handling.
64 // Return the bit size that this target implements. This should
68 { return this->pti_->size; }
70 // Return whether this target is big-endian.
73 { return this->pti_->is_big_endian; }
75 // Machine code to store in e_machine field of ELF header.
78 { return this->pti_->machine_code; }
80 // Whether this target has a specific make_symbol function.
82 has_make_symbol() const
83 { return this->pti_->has_make_symbol; }
85 // Whether this target has a specific resolve function.
88 { return this->pti_->has_resolve; }
90 // Whether this target has a specific code fill function.
93 { return this->pti_->has_code_fill; }
95 // Return the default name of the dynamic linker.
97 dynamic_linker() const
98 { return this->pti_->dynamic_linker; }
100 // Return the default address to use for the text segment.
102 default_text_segment_address() const
103 { return this->pti_->default_text_segment_address; }
105 // Return the ABI specified page size.
109 if (parameters->options().max_page_size() > 0)
110 return parameters->options().max_page_size();
112 return this->pti_->abi_pagesize;
115 // Return the common page size used on actual systems.
117 common_pagesize() const
119 if (parameters->options().common_page_size() > 0)
120 return std::min(parameters->options().common_page_size(),
121 this->abi_pagesize());
123 return std::min(this->pti_->common_pagesize,
124 this->abi_pagesize());
127 // If we see some object files with .note.GNU-stack sections, and
128 // some objects files without them, this returns whether we should
129 // consider the object files without them to imply that the stack
130 // should be executable.
132 is_default_stack_executable() const
133 { return this->pti_->is_default_stack_executable; }
135 // Return a character which may appear as a prefix for a wrap
136 // symbol. If this character appears, we strip it when checking for
137 // wrapping and add it back when forming the final symbol name.
138 // This should be '\0' if not special prefix is required, which is
142 { return this->pti_->wrap_char; }
144 // Return the special section index which indicates a small common
145 // symbol. This will return SHN_UNDEF if there are no small common
148 small_common_shndx() const
149 { return this->pti_->small_common_shndx; }
151 // Return values to add to the section flags for the section holding
152 // small common symbols.
154 small_common_section_flags() const
156 gold_assert(this->pti_->small_common_shndx != elfcpp::SHN_UNDEF);
157 return this->pti_->small_common_section_flags;
160 // Return the special section index which indicates a large common
161 // symbol. This will return SHN_UNDEF if there are no large common
164 large_common_shndx() const
165 { return this->pti_->large_common_shndx; }
167 // Return values to add to the section flags for the section holding
168 // large common symbols.
170 large_common_section_flags() const
172 gold_assert(this->pti_->large_common_shndx != elfcpp::SHN_UNDEF);
173 return this->pti_->large_common_section_flags;
176 // This hook is called when an output section is created.
178 new_output_section(Output_section* os) const
179 { this->do_new_output_section(os); }
181 // This is called to tell the target to complete any sections it is
182 // handling. After this all sections must have their final size.
184 finalize_sections(Layout* layout)
185 { return this->do_finalize_sections(layout); }
187 // Return the value to use for a global symbol which needs a special
188 // value in the dynamic symbol table. This will only be called if
189 // the backend first calls symbol->set_needs_dynsym_value().
191 dynsym_value(const Symbol* sym) const
192 { return this->do_dynsym_value(sym); }
194 // Return a string to use to fill out a code section. This is
195 // basically one or more NOPS which must fill out the specified
198 code_fill(section_size_type length) const
199 { return this->do_code_fill(length); }
201 // Return whether SYM is known to be defined by the ABI. This is
202 // used to avoid inappropriate warnings about undefined symbols.
204 is_defined_by_abi(const Symbol* sym) const
205 { return this->do_is_defined_by_abi(sym); }
207 // Adjust the output file header before it is written out. VIEW
208 // points to the header in external form. LEN is the length.
210 adjust_elf_header(unsigned char* view, int len) const
211 { return this->do_adjust_elf_header(view, len); }
213 // Return whether NAME is a local label name. This is used to implement the
214 // --discard-locals options.
216 is_local_label_name(const char* name) const
217 { return this->do_is_local_label_name(name); }
219 // Make an ELF object.
220 template<int size, bool big_endian>
222 make_elf_object(const std::string& name, Input_file* input_file,
223 off_t offset, const elfcpp::Ehdr<size, big_endian>& ehdr)
224 { return this->do_make_elf_object(name, input_file, offset, ehdr); }
227 // This struct holds the constant information for a child class. We
228 // use a struct to avoid the overhead of virtual function calls for
229 // simple information.
232 // Address size (32 or 64).
234 // Whether the target is big endian.
236 // The code to store in the e_machine field of the ELF header.
237 elfcpp::EM machine_code;
238 // Whether this target has a specific make_symbol function.
239 bool has_make_symbol;
240 // Whether this target has a specific resolve function.
242 // Whether this target has a specific code fill function.
244 // Whether an object file with no .note.GNU-stack sections implies
245 // that the stack should be executable.
246 bool is_default_stack_executable;
247 // Prefix character to strip when checking for wrapping.
249 // The default dynamic linker name.
250 const char* dynamic_linker;
251 // The default text segment address.
252 uint64_t default_text_segment_address;
253 // The ABI specified page size.
254 uint64_t abi_pagesize;
255 // The common page size used by actual implementations.
256 uint64_t common_pagesize;
257 // The special section index for small common symbols; SHN_UNDEF
259 elfcpp::Elf_Half small_common_shndx;
260 // The special section index for large common symbols; SHN_UNDEF
262 elfcpp::Elf_Half large_common_shndx;
263 // Section flags for small common section.
264 elfcpp::Elf_Xword small_common_section_flags;
265 // Section flags for large common section.
266 elfcpp::Elf_Xword large_common_section_flags;
269 Target(const Target_info* pti)
273 // Virtual function which may be implemented by the child class.
275 do_new_output_section(Output_section*) const
278 // Virtual function which may be implemented by the child class.
280 do_finalize_sections(Layout*)
283 // Virtual function which may be implemented by the child class.
285 do_dynsym_value(const Symbol*) const
286 { gold_unreachable(); }
288 // Virtual function which must be implemented by the child class if
291 do_code_fill(section_size_type) const
292 { gold_unreachable(); }
294 // Virtual function which may be implemented by the child class.
296 do_is_defined_by_abi(const Symbol*) const
299 // Adjust the output file header before it is written out. VIEW
300 // points to the header in external form. LEN is the length, and
301 // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.
302 // By default, we do nothing.
304 do_adjust_elf_header(unsigned char*, int) const
307 // Virtual function which may be overriden by the child class.
309 do_is_local_label_name(const char*) const;
311 // make_elf_object hooks. There are four versions of these for
312 // different address sizes and endianities.
314 #ifdef HAVE_TARGET_32_LITTLE
315 // Virtual functions which may be overriden by the child class.
317 do_make_elf_object(const std::string&, Input_file*, off_t,
318 const elfcpp::Ehdr<32, false>&);
321 #ifdef HAVE_TARGET_32_BIG
322 // Virtual functions which may be overriden by the child class.
324 do_make_elf_object(const std::string&, Input_file*, off_t,
325 const elfcpp::Ehdr<32, true>&);
328 #ifdef HAVE_TARGET_64_LITTLE
329 // Virtual functions which may be overriden by the child class.
331 do_make_elf_object(const std::string&, Input_file*, off_t,
332 const elfcpp::Ehdr<64, false>& ehdr);
335 #ifdef HAVE_TARGET_64_BIG
336 // Virtual functions which may be overriden by the child class.
338 do_make_elf_object(const std::string& name, Input_file* input_file,
339 off_t offset, const elfcpp::Ehdr<64, true>& ehdr);
343 // The implementations of the four do_make_elf_object virtual functions are
344 // almost identical except for their sizes and endianity. We use a template.
345 // for their implementations.
346 template<int size, bool big_endian>
348 do_make_elf_object_implementation(const std::string&, Input_file*, off_t,
349 const elfcpp::Ehdr<size, big_endian>&);
351 Target(const Target&);
352 Target& operator=(const Target&);
354 // The target information.
355 const Target_info* pti_;
358 // The abstract class for a specific size and endianness of target.
359 // Each actual target implementation class should derive from an
360 // instantiation of Sized_target.
362 template<int size, bool big_endian>
363 class Sized_target : public Target
366 // Make a new symbol table entry for the target. This should be
367 // overridden by a target which needs additional information in the
368 // symbol table. This will only be called if has_make_symbol()
370 virtual Sized_symbol<size>*
372 { gold_unreachable(); }
374 // Resolve a symbol for the target. This should be overridden by a
375 // target which needs to take special action. TO is the
376 // pre-existing symbol. SYM is the new symbol, seen in OBJECT.
377 // VERSION is the version of SYM. This will only be called if
378 // has_resolve() returns true.
380 resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
382 { gold_unreachable(); }
384 // Process the relocs for a section, and record information of the
385 // mapping from source to destination sections. This mapping is later
386 // used to determine unreferenced garbage sections. This procedure is
387 // only called during garbage collection.
389 gc_process_relocs(const General_options& options,
390 Symbol_table* symtab,
392 Sized_relobj<size, big_endian>* object,
393 unsigned int data_shndx,
394 unsigned int sh_type,
395 const unsigned char* prelocs,
397 Output_section* output_section,
398 bool needs_special_offset_handling,
399 size_t local_symbol_count,
400 const unsigned char* plocal_symbols) = 0;
402 // Scan the relocs for a section, and record any information
403 // required for the symbol. OPTIONS is the command line options.
404 // SYMTAB is the symbol table. OBJECT is the object in which the
405 // section appears. DATA_SHNDX is the section index that these
406 // relocs apply to. SH_TYPE is the type of the relocation section,
407 // SHT_REL or SHT_RELA. PRELOCS points to the relocation data.
408 // RELOC_COUNT is the number of relocs. LOCAL_SYMBOL_COUNT is the
409 // number of local symbols. OUTPUT_SECTION is the output section.
410 // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
411 // sections are not mapped as usual. PLOCAL_SYMBOLS points to the
412 // local symbol data from OBJECT. GLOBAL_SYMBOLS is the array of
413 // pointers to the global symbol table from OBJECT.
415 scan_relocs(const General_options& options,
416 Symbol_table* symtab,
418 Sized_relobj<size, big_endian>* object,
419 unsigned int data_shndx,
420 unsigned int sh_type,
421 const unsigned char* prelocs,
423 Output_section* output_section,
424 bool needs_special_offset_handling,
425 size_t local_symbol_count,
426 const unsigned char* plocal_symbols) = 0;
428 // Relocate section data. SH_TYPE is the type of the relocation
429 // section, SHT_REL or SHT_RELA. PRELOCS points to the relocation
430 // information. RELOC_COUNT is the number of relocs.
431 // OUTPUT_SECTION is the output section.
432 // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
433 // to correspond to the output section. VIEW is a view into the
434 // output file holding the section contents, VIEW_ADDRESS is the
435 // virtual address of the view, and VIEW_SIZE is the size of the
436 // view. If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
437 // parameters refer to the complete output section data, not just
438 // the input section data.
440 relocate_section(const Relocate_info<size, big_endian>*,
441 unsigned int sh_type,
442 const unsigned char* prelocs,
444 Output_section* output_section,
445 bool needs_special_offset_handling,
447 typename elfcpp::Elf_types<size>::Elf_Addr view_address,
448 section_size_type view_size) = 0;
450 // Scan the relocs during a relocatable link. The parameters are
451 // like scan_relocs, with an additional Relocatable_relocs
452 // parameter, used to record the disposition of the relocs.
454 scan_relocatable_relocs(const General_options& options,
455 Symbol_table* symtab,
457 Sized_relobj<size, big_endian>* object,
458 unsigned int data_shndx,
459 unsigned int sh_type,
460 const unsigned char* prelocs,
462 Output_section* output_section,
463 bool needs_special_offset_handling,
464 size_t local_symbol_count,
465 const unsigned char* plocal_symbols,
466 Relocatable_relocs*) = 0;
468 // Relocate a section during a relocatable link. The parameters are
469 // like relocate_section, with additional parameters for the view of
470 // the output reloc section.
472 relocate_for_relocatable(const Relocate_info<size, big_endian>*,
473 unsigned int sh_type,
474 const unsigned char* prelocs,
476 Output_section* output_section,
477 off_t offset_in_output_section,
478 const Relocatable_relocs*,
480 typename elfcpp::Elf_types<size>::Elf_Addr
482 section_size_type view_size,
483 unsigned char* reloc_view,
484 section_size_type reloc_view_size) = 0;
487 Sized_target(const Target::Target_info* pti)
490 gold_assert(pti->size == size);
491 gold_assert(pti->is_big_endian ? big_endian : !big_endian);
495 } // End namespace gold.
497 #endif // !defined(GOLD_TARGET_H)