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a2fb1b05 ILT |
1 | // layout.cc -- lay out output file sections for gold |
2 | ||
3 | #include "gold.h" | |
4 | ||
5 | #include <cassert> | |
6 | #include <cstring> | |
54dc6425 | 7 | #include <algorithm> |
a2fb1b05 ILT |
8 | #include <iostream> |
9 | #include <utility> | |
10 | ||
11 | #include "output.h" | |
12 | #include "layout.h" | |
13 | ||
14 | namespace gold | |
15 | { | |
16 | ||
17 | // Layout_task methods. | |
18 | ||
19 | Layout_task::~Layout_task() | |
20 | { | |
21 | } | |
22 | ||
23 | // This task can be run when it is unblocked. | |
24 | ||
25 | Task::Is_runnable_type | |
26 | Layout_task::is_runnable(Workqueue*) | |
27 | { | |
28 | if (this->this_blocker_->is_blocked()) | |
29 | return IS_BLOCKED; | |
30 | return IS_RUNNABLE; | |
31 | } | |
32 | ||
33 | // We don't need to hold any locks for the duration of this task. In | |
34 | // fact this task will be the only one running. | |
35 | ||
36 | Task_locker* | |
37 | Layout_task::locks(Workqueue*) | |
38 | { | |
39 | return NULL; | |
40 | } | |
41 | ||
42 | // Lay out the sections. This is called after all the input objects | |
43 | // have been read. | |
44 | ||
45 | void | |
46 | Layout_task::run(Workqueue*) | |
47 | { | |
48 | Layout layout(this->options_); | |
54dc6425 ILT |
49 | layout.init(); |
50 | for (Input_objects::Object_list::const_iterator p = | |
51 | this->input_objects_->begin(); | |
a2fb1b05 ILT |
52 | p != this->input_objects_->end(); |
53 | ++p) | |
54 | (*p)->layout(&layout); | |
54dc6425 | 55 | layout.finalize(this->input_objects_); |
a2fb1b05 ILT |
56 | } |
57 | ||
58 | // Layout methods. | |
59 | ||
54dc6425 ILT |
60 | Layout::Layout(const General_options& options) |
61 | : options_(options), namepool_(), signatures_(), | |
62 | section_name_map_(), segment_list_(), section_list_(), | |
63 | data_list_() | |
64 | { | |
65 | } | |
66 | ||
67 | // Prepare for doing layout. | |
68 | ||
69 | void | |
70 | Layout::init() | |
71 | { | |
72 | // Make space for more than enough segments for a typical file. | |
73 | // This is just for efficiency--it's OK if we wind up needing more. | |
74 | segment_list_.reserve(12); | |
75 | } | |
76 | ||
a2fb1b05 ILT |
77 | // Hash a key we use to look up an output section mapping. |
78 | ||
79 | size_t | |
80 | Layout::Hash_key::operator()(const Layout::Key& k) const | |
81 | { | |
82 | return reinterpret_cast<size_t>(k.first) + k.second.first + k.second.second; | |
83 | } | |
84 | ||
85 | // Whether to include this section in the link. | |
86 | ||
87 | template<int size, bool big_endian> | |
88 | bool | |
89 | Layout::include_section(Object*, const char*, | |
90 | const elfcpp::Shdr<size, big_endian>& shdr) | |
91 | { | |
92 | // Some section types are never linked. Some are only linked when | |
93 | // doing a relocateable link. | |
94 | switch (shdr.get_sh_type()) | |
95 | { | |
96 | case elfcpp::SHT_NULL: | |
97 | case elfcpp::SHT_SYMTAB: | |
98 | case elfcpp::SHT_DYNSYM: | |
99 | case elfcpp::SHT_STRTAB: | |
100 | case elfcpp::SHT_HASH: | |
101 | case elfcpp::SHT_DYNAMIC: | |
102 | case elfcpp::SHT_SYMTAB_SHNDX: | |
103 | return false; | |
104 | ||
105 | case elfcpp::SHT_RELA: | |
106 | case elfcpp::SHT_REL: | |
107 | case elfcpp::SHT_GROUP: | |
108 | return this->options_.is_relocatable(); | |
109 | ||
110 | default: | |
111 | // FIXME: Handle stripping debug sections here. | |
112 | return true; | |
113 | } | |
114 | } | |
115 | ||
116 | // Return the output section to use for input section NAME, with | |
117 | // header HEADER, from object OBJECT. Set *OFF to the offset of this | |
118 | // input section without the output section. | |
119 | ||
120 | template<int size, bool big_endian> | |
121 | Output_section* | |
122 | Layout::layout(Object* object, const char* name, | |
123 | const elfcpp::Shdr<size, big_endian>& shdr, off_t* off) | |
124 | { | |
125 | if (!this->include_section(object, name, shdr)) | |
126 | return NULL; | |
127 | ||
128 | // Unless we are doing a relocateable link, .gnu.linkonce sections | |
129 | // are laid out as though they were named for the sections are | |
130 | // placed into. | |
131 | if (!this->options_.is_relocatable() && Layout::is_linkonce(name)) | |
132 | name = Layout::linkonce_output_name(name); | |
133 | ||
134 | // FIXME: Handle SHF_OS_NONCONFORMING here. | |
135 | ||
136 | // Canonicalize the section name. | |
137 | name = this->namepool_.add(name); | |
138 | ||
139 | // Find the output section. The output section is selected based on | |
140 | // the section name, type, and flags. | |
141 | ||
142 | // FIXME: If we want to do relaxation, we need to modify this | |
143 | // algorithm. We also build a list of input sections for each | |
144 | // output section. Then we relax all the input sections. Then we | |
145 | // walk down the list and adjust all the offsets. | |
146 | ||
147 | elfcpp::Elf_Word type = shdr.get_sh_type(); | |
148 | elfcpp::Elf_Xword flags = shdr.get_sh_flags(); | |
149 | const Key key(name, std::make_pair(type, flags)); | |
150 | const std::pair<Key, Output_section*> v(key, NULL); | |
151 | std::pair<Section_name_map::iterator, bool> ins( | |
152 | this->section_name_map_.insert(v)); | |
153 | ||
154 | Output_section* os; | |
155 | if (!ins.second) | |
156 | os = ins.first->second; | |
157 | else | |
158 | { | |
159 | // This is the first time we've seen this name/type/flags | |
160 | // combination. | |
161 | os = this->make_output_section(name, type, flags); | |
162 | ins.first->second = os; | |
163 | } | |
164 | ||
165 | // FIXME: Handle SHF_LINK_ORDER somewhere. | |
166 | ||
167 | *off = os->add_input_section(object, name, shdr); | |
168 | ||
169 | return os; | |
170 | } | |
171 | ||
172 | // Return whether SEG1 should be before SEG2 in the output file. This | |
173 | // is based entirely on the segment type and flags. When this is | |
174 | // called the segment addresses has normally not yet been set. | |
175 | ||
176 | bool | |
177 | Layout::segment_precedes(const Output_segment* seg1, | |
178 | const Output_segment* seg2) | |
179 | { | |
180 | elfcpp::Elf_Word type1 = seg1->type(); | |
181 | elfcpp::Elf_Word type2 = seg2->type(); | |
182 | ||
183 | // The single PT_PHDR segment is required to precede any loadable | |
184 | // segment. We simply make it always first. | |
185 | if (type1 == elfcpp::PT_PHDR) | |
186 | { | |
187 | assert(type2 != elfcpp::PT_PHDR); | |
188 | return true; | |
189 | } | |
190 | if (type2 == elfcpp::PT_PHDR) | |
191 | return false; | |
192 | ||
193 | // The single PT_INTERP segment is required to precede any loadable | |
194 | // segment. We simply make it always second. | |
195 | if (type1 == elfcpp::PT_INTERP) | |
196 | { | |
197 | assert(type2 != elfcpp::PT_INTERP); | |
198 | return true; | |
199 | } | |
200 | if (type2 == elfcpp::PT_INTERP) | |
201 | return false; | |
202 | ||
203 | // We then put PT_LOAD segments before any other segments. | |
204 | if (type1 == elfcpp::PT_LOAD && type2 != elfcpp::PT_LOAD) | |
205 | return true; | |
206 | if (type2 == elfcpp::PT_LOAD && type1 != elfcpp::PT_LOAD) | |
207 | return false; | |
208 | ||
209 | const elfcpp::Elf_Word flags1 = seg1->flags(); | |
210 | const elfcpp::Elf_Word flags2 = seg2->flags(); | |
211 | ||
212 | // The order of non-PT_LOAD segments is unimportant. We simply sort | |
213 | // by the numeric segment type and flags values. There should not | |
214 | // be more than one segment with the same type and flags. | |
215 | if (type1 != elfcpp::PT_LOAD) | |
216 | { | |
217 | if (type1 != type2) | |
218 | return type1 < type2; | |
219 | assert(flags1 != flags2); | |
220 | return flags1 < flags2; | |
221 | } | |
222 | ||
223 | // We sort PT_LOAD segments based on the flags. Readonly segments | |
224 | // come before writable segments. Then executable segments come | |
225 | // before non-executable segments. Then the unlikely case of a | |
226 | // non-readable segment comes before the normal case of a readable | |
227 | // segment. If there are multiple segments with the same type and | |
228 | // flags, we require that the address be set, and we sort by | |
229 | // virtual address and then physical address. | |
230 | if ((flags1 & elfcpp::PF_W) != (flags2 & elfcpp::PF_W)) | |
231 | return (flags1 & elfcpp::PF_W) == 0; | |
232 | if ((flags1 & elfcpp::PF_X) != (flags2 & elfcpp::PF_X)) | |
233 | return (flags1 & elfcpp::PF_X) != 0; | |
234 | if ((flags1 & elfcpp::PF_R) != (flags2 & elfcpp::PF_R)) | |
235 | return (flags1 & elfcpp::PF_R) == 0; | |
236 | ||
237 | uint64_t vaddr1 = seg1->vaddr(); | |
238 | uint64_t vaddr2 = seg2->vaddr(); | |
239 | if (vaddr1 != vaddr2) | |
240 | return vaddr1 < vaddr2; | |
241 | ||
242 | uint64_t paddr1 = seg1->paddr(); | |
243 | uint64_t paddr2 = seg2->paddr(); | |
244 | assert(paddr1 != paddr2); | |
245 | return paddr1 < paddr2; | |
246 | } | |
247 | ||
248 | // Map section flags to segment flags. | |
249 | ||
250 | elfcpp::Elf_Word | |
251 | Layout::section_flags_to_segment(elfcpp::Elf_Xword flags) | |
252 | { | |
253 | elfcpp::Elf_Word ret = elfcpp::PF_R; | |
254 | if ((flags & elfcpp::SHF_WRITE) != 0) | |
255 | ret |= elfcpp::PF_W; | |
256 | if ((flags & elfcpp::SHF_EXECINSTR) != 0) | |
257 | ret |= elfcpp::PF_X; | |
258 | return ret; | |
259 | } | |
260 | ||
261 | // Make a new Output_section, and attach it to segments as | |
262 | // appropriate. | |
263 | ||
264 | Output_section* | |
265 | Layout::make_output_section(const char* name, elfcpp::Elf_Word type, | |
266 | elfcpp::Elf_Xword flags) | |
267 | { | |
268 | Output_section* os = new Output_section(name, type, flags); | |
269 | ||
270 | if ((flags & elfcpp::SHF_ALLOC) == 0) | |
271 | this->section_list_.push_back(os); | |
272 | else | |
273 | { | |
274 | // This output section goes into a PT_LOAD segment. | |
275 | ||
276 | elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags); | |
277 | ||
278 | // The only thing we really care about for PT_LOAD segments is | |
279 | // whether or not they are writable, so that is how we search | |
280 | // for them. People who need segments sorted on some other | |
281 | // basis will have to wait until we implement a mechanism for | |
282 | // them to describe the segments they want. | |
283 | ||
284 | Segment_list::const_iterator p; | |
285 | for (p = this->segment_list_.begin(); | |
286 | p != this->segment_list_.end(); | |
287 | ++p) | |
288 | { | |
289 | if ((*p)->type() == elfcpp::PT_LOAD | |
290 | && ((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W)) | |
291 | { | |
292 | (*p)->add_output_section(os); | |
a2fb1b05 ILT |
293 | break; |
294 | } | |
295 | } | |
296 | ||
297 | if (p == this->segment_list_.end()) | |
298 | { | |
299 | Output_segment* oseg = new Output_segment(elfcpp::PT_LOAD, | |
300 | seg_flags); | |
301 | this->segment_list_.push_back(oseg); | |
302 | oseg->add_output_section(os); | |
303 | } | |
304 | ||
305 | // If we see a loadable SHT_NOTE section, we create a PT_NOTE | |
306 | // segment. | |
307 | if (type == elfcpp::SHT_NOTE) | |
308 | { | |
309 | // See if we already have an equivalent PT_NOTE segment. | |
310 | for (p = this->segment_list_.begin(); | |
311 | p != segment_list_.end(); | |
312 | ++p) | |
313 | { | |
314 | if ((*p)->type() == elfcpp::PT_NOTE | |
315 | && (((*p)->flags() & elfcpp::PF_W) | |
316 | == (seg_flags & elfcpp::PF_W))) | |
317 | { | |
318 | (*p)->add_output_section(os); | |
a2fb1b05 ILT |
319 | break; |
320 | } | |
321 | } | |
322 | ||
323 | if (p == this->segment_list_.end()) | |
324 | { | |
325 | Output_segment* oseg = new Output_segment(elfcpp::PT_NOTE, | |
326 | seg_flags); | |
327 | this->segment_list_.push_back(oseg); | |
328 | oseg->add_output_section(os); | |
329 | } | |
330 | } | |
54dc6425 ILT |
331 | |
332 | // If we see a loadable SHF_TLS section, we create a PT_TLS | |
333 | // segment. | |
334 | if ((flags & elfcpp::SHF_TLS) != 0) | |
335 | { | |
336 | // See if we already have an equivalent PT_TLS segment. | |
337 | for (p = this->segment_list_.begin(); | |
338 | p != segment_list_.end(); | |
339 | ++p) | |
340 | { | |
341 | if ((*p)->type() == elfcpp::PT_TLS | |
342 | && (((*p)->flags() & elfcpp::PF_W) | |
343 | == (seg_flags & elfcpp::PF_W))) | |
344 | { | |
345 | (*p)->add_output_section(os); | |
346 | break; | |
347 | } | |
348 | } | |
349 | ||
350 | if (p == this->segment_list_.end()) | |
351 | { | |
352 | Output_segment* oseg = new Output_segment(elfcpp::PT_TLS, | |
353 | seg_flags); | |
354 | this->segment_list_.push_back(oseg); | |
355 | oseg->add_output_section(os); | |
356 | } | |
357 | } | |
a2fb1b05 ILT |
358 | } |
359 | ||
360 | return os; | |
361 | } | |
362 | ||
54dc6425 ILT |
363 | // Create the sections for the symbol table. |
364 | ||
365 | void | |
366 | Layout::create_symtab_sections() | |
367 | { | |
368 | } | |
369 | ||
370 | // Finalize the layout. When this is called, we have created all the | |
371 | // output sections and all the output segments which are based on | |
372 | // input sections. We have several things to do, and we have to do | |
373 | // them in the right order, so that we get the right results correctly | |
374 | // and efficiently. | |
375 | ||
376 | // 1) Finalize the list of output segments and create the segment | |
377 | // table header. | |
378 | ||
379 | // 2) Finalize the dynamic symbol table and associated sections. | |
380 | ||
381 | // 3) Determine the final file offset of all the output segments. | |
382 | ||
383 | // 4) Determine the final file offset of all the SHF_ALLOC output | |
384 | // sections. | |
385 | ||
386 | // 5) Finalize the symbol table: set symbol values to their final | |
387 | // value and make a final determination of which symbols are going | |
388 | // into the output symbol table. | |
389 | ||
390 | // 6) Create the symbol table sections and the section name table | |
391 | // section. | |
392 | ||
393 | // 7) Create the section table header. | |
394 | ||
395 | // 8) Determine the final file offset of all the output sections which | |
396 | // are not SHF_ALLOC, including the section table header. | |
397 | ||
398 | // 9) Finalize the ELF file header. | |
399 | ||
400 | void | |
401 | Layout::finalize(const Input_objects* input_objects) | |
402 | { | |
403 | if (input_objects->any_dynamic()) | |
404 | { | |
405 | // If there are any dynamic objects in the link, then we need | |
406 | // some additional segments: PT_PHDRS, PT_INTERP, and | |
407 | // PT_DYNAMIC. We also need to finalize the dynamic symbol | |
408 | // table and create the dynamic hash table. | |
409 | abort(); | |
410 | } | |
411 | ||
412 | // FIXME: Handle PT_GNU_STACK. | |
413 | ||
414 | std::sort(this->segment_list_.begin(), this->segment_list_.end(), | |
415 | Layout::Compare_segments()); | |
416 | ||
417 | Output_segment_headers* segment_headers; | |
418 | segment_headers = new Output_segment_headers(this->segment_list_); | |
419 | } | |
420 | ||
a2fb1b05 ILT |
421 | // The mapping of .gnu.linkonce section names to real section names. |
422 | ||
423 | #define MAPPING_INIT(f, t) { f, sizeof(f) - 1, t } | |
424 | const Layout::Linkonce_mapping Layout::linkonce_mapping[] = | |
425 | { | |
426 | MAPPING_INIT("d.rel.ro", ".data.rel.ro"), // Must be before "d". | |
427 | MAPPING_INIT("t", ".text"), | |
428 | MAPPING_INIT("r", ".rodata"), | |
429 | MAPPING_INIT("d", ".data"), | |
430 | MAPPING_INIT("b", ".bss"), | |
431 | MAPPING_INIT("s", ".sdata"), | |
432 | MAPPING_INIT("sb", ".sbss"), | |
433 | MAPPING_INIT("s2", ".sdata2"), | |
434 | MAPPING_INIT("sb2", ".sbss2"), | |
435 | MAPPING_INIT("wi", ".debug_info"), | |
436 | MAPPING_INIT("td", ".tdata"), | |
437 | MAPPING_INIT("tb", ".tbss"), | |
438 | MAPPING_INIT("lr", ".lrodata"), | |
439 | MAPPING_INIT("l", ".ldata"), | |
440 | MAPPING_INIT("lb", ".lbss"), | |
441 | }; | |
442 | #undef MAPPING_INIT | |
443 | ||
444 | const int Layout::linkonce_mapping_count = | |
445 | sizeof(Layout::linkonce_mapping) / sizeof(Layout::linkonce_mapping[0]); | |
446 | ||
447 | // Return the name of the output section to use for a .gnu.linkonce | |
448 | // section. This is based on the default ELF linker script of the old | |
449 | // GNU linker. For example, we map a name like ".gnu.linkonce.t.foo" | |
450 | // to ".text". | |
451 | ||
452 | const char* | |
453 | Layout::linkonce_output_name(const char* name) | |
454 | { | |
455 | const char* s = name + sizeof(".gnu.linkonce") - 1; | |
456 | if (*s != '.') | |
457 | return name; | |
458 | ++s; | |
459 | const Linkonce_mapping* plm = linkonce_mapping; | |
460 | for (int i = 0; i < linkonce_mapping_count; ++i, ++plm) | |
461 | { | |
462 | if (strncmp(s, plm->from, plm->fromlen) == 0 && s[plm->fromlen] == '.') | |
463 | return plm->to; | |
464 | } | |
465 | return name; | |
466 | } | |
467 | ||
468 | // Record the signature of a comdat section, and return whether to | |
469 | // include it in the link. If GROUP is true, this is a regular | |
470 | // section group. If GROUP is false, this is a group signature | |
471 | // derived from the name of a linkonce section. We want linkonce | |
472 | // signatures and group signatures to block each other, but we don't | |
473 | // want a linkonce signature to block another linkonce signature. | |
474 | ||
475 | bool | |
476 | Layout::add_comdat(const char* signature, bool group) | |
477 | { | |
478 | std::string sig(signature); | |
479 | std::pair<Signatures::iterator, bool> ins( | |
480 | this->signatures_.insert(std::make_pair(signature, group))); | |
481 | ||
482 | if (ins.second) | |
483 | { | |
484 | // This is the first time we've seen this signature. | |
485 | return true; | |
486 | } | |
487 | ||
488 | if (ins.first->second) | |
489 | { | |
490 | // We've already seen a real section group with this signature. | |
491 | return false; | |
492 | } | |
493 | else if (group) | |
494 | { | |
495 | // This is a real section group, and we've already seen a | |
496 | // linkonce section with tihs signature. Record that we've seen | |
497 | // a section group, and don't include this section group. | |
498 | ins.first->second = true; | |
499 | return false; | |
500 | } | |
501 | else | |
502 | { | |
503 | // We've already seen a linkonce section and this is a linkonce | |
504 | // section. These don't block each other--this may be the same | |
505 | // symbol name with different section types. | |
506 | return true; | |
507 | } | |
508 | } | |
509 | ||
510 | // Instantiate the templates we need. We could use the configure | |
511 | // script to restrict this to only the ones for implemented targets. | |
512 | ||
513 | template | |
514 | Output_section* | |
515 | Layout::layout<32, false>(Object* object, const char* name, | |
516 | const elfcpp::Shdr<32, false>& shdr, off_t*); | |
517 | ||
518 | template | |
519 | Output_section* | |
520 | Layout::layout<32, true>(Object* object, const char* name, | |
521 | const elfcpp::Shdr<32, true>& shdr, off_t*); | |
522 | ||
523 | template | |
524 | Output_section* | |
525 | Layout::layout<64, false>(Object* object, const char* name, | |
526 | const elfcpp::Shdr<64, false>& shdr, off_t*); | |
527 | ||
528 | template | |
529 | Output_section* | |
530 | Layout::layout<64, true>(Object* object, const char* name, | |
531 | const elfcpp::Shdr<64, true>& shdr, off_t*); | |
532 | ||
533 | ||
534 | } // End namespace gold. |