1 // merge.cc -- handle section merging for gold
2 
3 // Copyright (C) 2006-2021 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 <cstdlib>
26 #include <algorithm>
27 
28 #include "merge.h"
29 #include "compressed_output.h"
30 
31 namespace gold
32 {
33 
34 // Class Object_merge_map.
35 
36 // Destructor.
37 
~Object_merge_map()38 Object_merge_map::~Object_merge_map()
39 {
40   for (Section_merge_maps::iterator p = this->section_merge_maps_.begin();
41        p != this->section_merge_maps_.end();
42        ++p)
43     delete p->second;
44 }
45 
46 // Get the Input_merge_map to use for an input section, or NULL.
47 
48 const Object_merge_map::Input_merge_map*
get_input_merge_map(unsigned int shndx) const49 Object_merge_map::get_input_merge_map(unsigned int shndx) const
50 {
51   gold_assert(shndx != -1U);
52   const Section_merge_maps &maps = this->section_merge_maps_;
53   for (Section_merge_maps::const_iterator i = maps.begin(), e = maps.end();
54        i != e; ++i)
55     {
56       if (i->first == shndx)
57 	return i->second;
58     }
59   return NULL;
60 }
61 
62 // Get or create the Input_merge_map to use for an input section.
63 
64 Object_merge_map::Input_merge_map*
get_or_make_input_merge_map(const Output_section_data * output_data,unsigned int shndx)65 Object_merge_map::get_or_make_input_merge_map(
66     const Output_section_data* output_data, unsigned int shndx) {
67   Input_merge_map* map = this->get_input_merge_map(shndx);
68   if (map != NULL)
69     {
70       // For a given input section in a given object, every mapping
71       // must be done with the same Merge_map.
72       gold_assert(map->output_data == output_data);
73       return map;
74     }
75 
76   Input_merge_map* new_map = new Input_merge_map;
77   new_map->output_data = output_data;
78   Section_merge_maps &maps = this->section_merge_maps_;
79   maps.push_back(std::make_pair(shndx, new_map));
80   return new_map;
81 }
82 
83 // Add a mapping.
84 
85 void
add_mapping(const Output_section_data * output_data,unsigned int shndx,section_offset_type input_offset,section_size_type length,section_offset_type output_offset)86 Object_merge_map::add_mapping(const Output_section_data* output_data,
87 			      unsigned int shndx,
88 			      section_offset_type input_offset,
89 			      section_size_type length,
90 			      section_offset_type output_offset)
91 {
92   Input_merge_map* map = this->get_or_make_input_merge_map(output_data, shndx);
93   map->add_mapping(input_offset, length, output_offset);
94 }
95 
96 void
add_mapping(section_offset_type input_offset,section_size_type length,section_offset_type output_offset)97 Object_merge_map::Input_merge_map::add_mapping(
98     section_offset_type input_offset, section_size_type length,
99     section_offset_type output_offset) {
100   // Try to merge the new entry in the last one we saw.
101   if (!this->entries.empty())
102     {
103       Input_merge_entry& entry(this->entries.back());
104 
105       // Use section_size_type to avoid signed/unsigned warnings.
106       section_size_type input_offset_u = input_offset;
107       section_size_type output_offset_u = output_offset;
108 
109       // If this entry is not in order, we need to sort the vector
110       // before looking anything up.
111       if (input_offset_u < entry.input_offset + entry.length)
112 	{
113 	  gold_assert(input_offset < entry.input_offset);
114 	  gold_assert(input_offset_u + length
115 		      <= static_cast<section_size_type>(entry.input_offset));
116 	  this->sorted = false;
117 	}
118       else if (entry.input_offset + entry.length == input_offset_u
119 	       && (output_offset == -1
120 		   ? entry.output_offset == -1
121 		   : entry.output_offset + entry.length == output_offset_u))
122 	{
123 	  entry.length += length;
124 	  return;
125 	}
126     }
127 
128   Input_merge_entry entry;
129   entry.input_offset = input_offset;
130   entry.length = length;
131   entry.output_offset = output_offset;
132   this->entries.push_back(entry);
133 }
134 
135 // Get the output offset for an input address.
136 
137 bool
get_output_offset(unsigned int shndx,section_offset_type input_offset,section_offset_type * output_offset)138 Object_merge_map::get_output_offset(unsigned int shndx,
139 				    section_offset_type input_offset,
140 				    section_offset_type* output_offset)
141 {
142   Input_merge_map* map = this->get_input_merge_map(shndx);
143   if (map == NULL)
144     return false;
145 
146   if (!map->sorted)
147     {
148       std::sort(map->entries.begin(), map->entries.end(),
149 		Input_merge_compare());
150       map->sorted = true;
151     }
152 
153   Input_merge_entry entry;
154   entry.input_offset = input_offset;
155   std::vector<Input_merge_entry>::const_iterator p =
156     std::upper_bound(map->entries.begin(), map->entries.end(),
157 		     entry, Input_merge_compare());
158   if (p == map->entries.begin())
159     return false;
160   --p;
161   gold_assert(p->input_offset <= input_offset);
162 
163   if (input_offset - p->input_offset
164       >= static_cast<section_offset_type>(p->length))
165     return false;
166 
167   *output_offset = p->output_offset;
168   if (*output_offset != -1)
169     *output_offset += (input_offset - p->input_offset);
170   return true;
171 }
172 
173 // Return whether this is the merge map for section SHNDX.
174 
175 const Output_section_data*
find_merge_section(unsigned int shndx) const176 Object_merge_map::find_merge_section(unsigned int shndx) const {
177   const Object_merge_map::Input_merge_map* map =
178     this->get_input_merge_map(shndx);
179   if (map == NULL)
180     return NULL;
181   return map->output_data;
182 }
183 
184 // Initialize a mapping from input offsets to output addresses.
185 
186 template<int size>
187 void
initialize_input_to_output_map(unsigned int shndx,typename elfcpp::Elf_types<size>::Elf_Addr starting_address,Unordered_map<section_offset_type,typename elfcpp::Elf_types<size>::Elf_Addr> * initialize_map)188 Object_merge_map::initialize_input_to_output_map(
189     unsigned int shndx,
190     typename elfcpp::Elf_types<size>::Elf_Addr starting_address,
191     Unordered_map<section_offset_type,
192 		  typename elfcpp::Elf_types<size>::Elf_Addr>* initialize_map)
193 {
194   Input_merge_map* map = this->get_input_merge_map(shndx);
195   gold_assert(map != NULL);
196 
197   gold_assert(initialize_map->empty());
198   // We know how many entries we are going to add.
199   // reserve_unordered_map takes an expected count of buckets, not a
200   // count of elements, so double it to try to reduce collisions.
201   reserve_unordered_map(initialize_map, map->entries.size() * 2);
202 
203   for (Input_merge_map::Entries::const_iterator p = map->entries.begin();
204        p != map->entries.end();
205        ++p)
206     {
207       section_offset_type output_offset = p->output_offset;
208       if (output_offset != -1)
209 	output_offset += starting_address;
210       else
211 	{
212 	  // If we see a relocation against an address we have chosen
213 	  // to discard, we relocate to zero.  FIXME: We could also
214 	  // issue a warning in this case; that would require
215 	  // reporting this somehow and checking it in the routines in
216 	  // reloc.h.
217 	  output_offset = 0;
218 	}
219       initialize_map->insert(std::make_pair(p->input_offset, output_offset));
220     }
221 }
222 
223 // Class Output_merge_base.
224 
225 // Return the output offset for an input offset.  The input address is
226 // at offset OFFSET in section SHNDX in OBJECT.  If we know the
227 // offset, set *POUTPUT and return true.  Otherwise return false.
228 
229 bool
do_output_offset(const Relobj * object,unsigned int shndx,section_offset_type offset,section_offset_type * poutput) const230 Output_merge_base::do_output_offset(const Relobj* object,
231 				    unsigned int shndx,
232 				    section_offset_type offset,
233 				    section_offset_type* poutput) const
234 {
235   return object->merge_output_offset(shndx, offset, poutput);
236 }
237 
238 // Record a merged input section for script processing.
239 
240 void
record_input_section(Relobj * relobj,unsigned int shndx)241 Output_merge_base::record_input_section(Relobj* relobj, unsigned int shndx)
242 {
243   gold_assert(this->keeps_input_sections_ && relobj != NULL);
244   // If this is the first input section, record it.  We need do this because
245   // this->input_sections_ is unordered.
246   if (this->first_relobj_ == NULL)
247     {
248       this->first_relobj_ = relobj;
249       this->first_shndx_ = shndx;
250     }
251 
252   std::pair<Input_sections::iterator, bool> result =
253     this->input_sections_.insert(Section_id(relobj, shndx));
254   // We should insert a merge section once only.
255   gold_assert(result.second);
256 }
257 
258 // Class Output_merge_data.
259 
260 // Compute the hash code for a fixed-size constant.
261 
262 size_t
operator ()(Merge_data_key k) const263 Output_merge_data::Merge_data_hash::operator()(Merge_data_key k) const
264 {
265   const unsigned char* p = this->pomd_->constant(k);
266   section_size_type entsize =
267     convert_to_section_size_type(this->pomd_->entsize());
268 
269   // Fowler/Noll/Vo (FNV) hash (type FNV-1a).
270   if (sizeof(size_t) == 8)
271     {
272       size_t result = static_cast<size_t>(14695981039346656037ULL);
273       for (section_size_type i = 0; i < entsize; ++i)
274 	{
275 	  result &= (size_t) *p++;
276 	  result *= 1099511628211ULL;
277 	}
278       return result;
279     }
280   else
281     {
282       size_t result = 2166136261UL;
283       for (section_size_type i = 0; i < entsize; ++i)
284 	{
285 	  result ^= (size_t) *p++;
286 	  result *= 16777619UL;
287 	}
288       return result;
289     }
290 }
291 
292 // Return whether one hash table key equals another.
293 
294 bool
operator ()(Merge_data_key k1,Merge_data_key k2) const295 Output_merge_data::Merge_data_eq::operator()(Merge_data_key k1,
296 					     Merge_data_key k2) const
297 {
298   const unsigned char* p1 = this->pomd_->constant(k1);
299   const unsigned char* p2 = this->pomd_->constant(k2);
300   return memcmp(p1, p2, this->pomd_->entsize()) == 0;
301 }
302 
303 // Add a constant to the end of the section contents.
304 
305 void
add_constant(const unsigned char * p)306 Output_merge_data::add_constant(const unsigned char* p)
307 {
308   section_size_type entsize = convert_to_section_size_type(this->entsize());
309   section_size_type addralign =
310     convert_to_section_size_type(this->addralign());
311   section_size_type addsize = std::max(entsize, addralign);
312   if (this->len_ + addsize > this->alc_)
313     {
314       if (this->alc_ == 0)
315 	this->alc_ = 128 * addsize;
316       else
317 	this->alc_ *= 2;
318       this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->alc_));
319       if (this->p_ == NULL)
320 	gold_nomem();
321     }
322 
323   memcpy(this->p_ + this->len_, p, entsize);
324   if (addsize > entsize)
325     memset(this->p_ + this->len_ + entsize, 0, addsize - entsize);
326   this->len_ += addsize;
327 }
328 
329 // Add the input section SHNDX in OBJECT to a merged output section
330 // which holds fixed length constants.  Return whether we were able to
331 // handle the section; if not, it will be linked as usual without
332 // constant merging.
333 
334 bool
do_add_input_section(Relobj * object,unsigned int shndx)335 Output_merge_data::do_add_input_section(Relobj* object, unsigned int shndx)
336 {
337   section_size_type len;
338   bool is_new;
339   const unsigned char* p = object->decompressed_section_contents(shndx, &len,
340 								 &is_new);
341 
342   section_size_type entsize = convert_to_section_size_type(this->entsize());
343 
344   if (len % entsize != 0)
345     {
346       if (is_new)
347 	delete[] p;
348       return false;
349     }
350 
351   this->input_count_ += len / entsize;
352 
353   Object_merge_map* merge_map = object->get_or_create_merge_map();
354   Object_merge_map::Input_merge_map* input_merge_map =
355     merge_map->get_or_make_input_merge_map(this, shndx);
356 
357   for (section_size_type i = 0; i < len; i += entsize, p += entsize)
358     {
359       // Add the constant to the section contents.  If we find that it
360       // is already in the hash table, we will remove it again.
361       Merge_data_key k = this->len_;
362       this->add_constant(p);
363 
364       std::pair<Merge_data_hashtable::iterator, bool> ins =
365 	this->hashtable_.insert(k);
366 
367       if (!ins.second)
368 	{
369 	  // Key was already present.  Remove the copy we just added.
370 	  this->len_ -= entsize;
371 	  k = *ins.first;
372 	}
373 
374       // Record the offset of this constant in the output section.
375       input_merge_map->add_mapping(i, entsize, k);
376     }
377 
378   // For script processing, we keep the input sections.
379   if (this->keeps_input_sections())
380     record_input_section(object, shndx);
381 
382   if (is_new)
383     delete[] p;
384 
385   return true;
386 }
387 
388 // Set the final data size in a merged output section with fixed size
389 // constants.
390 
391 void
set_final_data_size()392 Output_merge_data::set_final_data_size()
393 {
394   // Release the memory we don't need.
395   this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->len_));
396   // An Output_merge_data object may be empty and realloc is allowed
397   // to return a NULL pointer in this case.  An Output_merge_data is empty
398   // if all its input sections have sizes that are not multiples of entsize.
399   gold_assert(this->p_ != NULL || this->len_ == 0);
400   this->set_data_size(this->len_);
401 }
402 
403 // Write the data of a merged output section with fixed size constants
404 // to the file.
405 
406 void
do_write(Output_file * of)407 Output_merge_data::do_write(Output_file* of)
408 {
409   of->write(this->offset(), this->p_, this->len_);
410 }
411 
412 // Write the data to a buffer.
413 
414 void
do_write_to_buffer(unsigned char * buffer)415 Output_merge_data::do_write_to_buffer(unsigned char* buffer)
416 {
417   memcpy(buffer, this->p_, this->len_);
418 }
419 
420 // Print merge stats to stderr.
421 
422 void
do_print_merge_stats(const char * section_name)423 Output_merge_data::do_print_merge_stats(const char* section_name)
424 {
425   fprintf(stderr,
426 	  _("%s: %s merged constants size: %lu; input: %zu; output: %zu\n"),
427 	  program_name, section_name,
428 	  static_cast<unsigned long>(this->entsize()),
429 	  this->input_count_, this->hashtable_.size());
430 }
431 
432 // Class Output_merge_string.
433 
434 // Add an input section to a merged string section.
435 
436 template<typename Char_type>
437 bool
do_add_input_section(Relobj * object,unsigned int shndx)438 Output_merge_string<Char_type>::do_add_input_section(Relobj* object,
439 						     unsigned int shndx)
440 {
441   section_size_type sec_len;
442   bool is_new;
443   uint64_t addralign = this->addralign();
444   const unsigned char* pdata = object->decompressed_section_contents(shndx,
445 								     &sec_len,
446 								     &is_new,
447 								     &addralign);
448 
449   const Char_type* p = reinterpret_cast<const Char_type*>(pdata);
450   const Char_type* pend = p + sec_len / sizeof(Char_type);
451   const Char_type* pend0 = pend;
452 
453   if (sec_len % sizeof(Char_type) != 0)
454     {
455       object->error(_("mergeable string section length not multiple of "
456 		      "character size"));
457       if (is_new)
458 	delete[] pdata;
459       return false;
460     }
461 
462   if (pend[-1] != 0)
463     {
464       gold_warning(_("%s: last entry in mergeable string section '%s' "
465 		     "not null terminated"),
466 		   object->name().c_str(),
467 		   object->section_name(shndx).c_str());
468       // Find the end of the last NULL-terminated string in the buffer.
469       while (pend0 > p && pend0[-1] != 0)
470 	--pend0;
471     }
472 
473   Merged_strings_list* merged_strings_list =
474       new Merged_strings_list(object, shndx);
475   this->merged_strings_lists_.push_back(merged_strings_list);
476   Merged_strings& merged_strings = merged_strings_list->merged_strings;
477 
478   // Count the number of non-null strings in the section and size the list.
479   size_t count = 0;
480   const Char_type* pt = p;
481   while (pt < pend0)
482     {
483       size_t len = string_length(pt);
484       if (len != 0)
485 	++count;
486       pt += len + 1;
487     }
488   if (pend0 < pend)
489     ++count;
490   merged_strings.reserve(count + 1);
491 
492   // The index I is in bytes, not characters.
493   section_size_type i = 0;
494 
495   // We assume here that the beginning of the section is correctly
496   // aligned, so each string within the section must retain the same
497   // modulo.
498   uintptr_t init_align_modulo = (reinterpret_cast<uintptr_t>(pdata)
499 				 & (addralign - 1));
500   bool has_misaligned_strings = false;
501 
502   while (p < pend)
503     {
504       size_t len = p < pend0 ? string_length(p) : pend - p;
505 
506       // Within merge input section each string must be aligned.
507       if (len != 0
508 	  && ((reinterpret_cast<uintptr_t>(p) & (addralign - 1))
509 	      != init_align_modulo))
510 	  has_misaligned_strings = true;
511 
512       Stringpool::Key key;
513       this->stringpool_.add_with_length(p, len, true, &key);
514 
515       merged_strings.push_back(Merged_string(i, key));
516       p += len + 1;
517       i += (len + 1) * sizeof(Char_type);
518     }
519 
520   // Record the last offset in the input section so that we can
521   // compute the length of the last string.
522   merged_strings.push_back(Merged_string(i, 0));
523 
524   this->input_count_ += count;
525   this->input_size_ += i;
526 
527   if (has_misaligned_strings)
528     gold_warning(_("%s: section %s contains incorrectly aligned strings;"
529 		   " the alignment of those strings won't be preserved"),
530 		 object->name().c_str(),
531 		 object->section_name(shndx).c_str());
532 
533   // For script processing, we keep the input sections.
534   if (this->keeps_input_sections())
535     record_input_section(object, shndx);
536 
537   if (is_new)
538     delete[] pdata;
539 
540   return true;
541 }
542 
543 // Finalize the mappings from the input sections to the output
544 // section, and return the final data size.
545 
546 template<typename Char_type>
547 section_size_type
finalize_merged_data()548 Output_merge_string<Char_type>::finalize_merged_data()
549 {
550   this->stringpool_.set_string_offsets();
551 
552   for (typename Merged_strings_lists::const_iterator l =
553 	 this->merged_strings_lists_.begin();
554        l != this->merged_strings_lists_.end();
555        ++l)
556     {
557       section_offset_type last_input_offset = 0;
558       section_offset_type last_output_offset = 0;
559       Relobj *object = (*l)->object;
560       Object_merge_map* merge_map = object->get_or_create_merge_map();
561       Object_merge_map::Input_merge_map* input_merge_map =
562         merge_map->get_or_make_input_merge_map(this, (*l)->shndx);
563 
564       for (typename Merged_strings::const_iterator p =
565 	     (*l)->merged_strings.begin();
566 	   p != (*l)->merged_strings.end();
567 	   ++p)
568 	{
569 	  section_size_type length = p->offset - last_input_offset;
570 	  if (length > 0)
571 	    input_merge_map->add_mapping(last_input_offset, length,
572                                          last_output_offset);
573 	  last_input_offset = p->offset;
574 	  if (p->stringpool_key != 0)
575 	    last_output_offset =
576 	        this->stringpool_.get_offset_from_key(p->stringpool_key);
577 	}
578       delete *l;
579     }
580 
581   // Save some memory.  This also ensures that this function will work
582   // if called twice, as may happen if Layout::set_segment_offsets
583   // finds a better alignment.
584   this->merged_strings_lists_.clear();
585 
586   return this->stringpool_.get_strtab_size();
587 }
588 
589 template<typename Char_type>
590 void
set_final_data_size()591 Output_merge_string<Char_type>::set_final_data_size()
592 {
593   const off_t final_data_size = this->finalize_merged_data();
594   this->set_data_size(final_data_size);
595 }
596 
597 // Write out a merged string section.
598 
599 template<typename Char_type>
600 void
do_write(Output_file * of)601 Output_merge_string<Char_type>::do_write(Output_file* of)
602 {
603   this->stringpool_.write(of, this->offset());
604 }
605 
606 // Write a merged string section to a buffer.
607 
608 template<typename Char_type>
609 void
do_write_to_buffer(unsigned char * buffer)610 Output_merge_string<Char_type>::do_write_to_buffer(unsigned char* buffer)
611 {
612   this->stringpool_.write_to_buffer(buffer, this->data_size());
613 }
614 
615 // Return the name of the types of string to use with
616 // do_print_merge_stats.
617 
618 template<typename Char_type>
619 const char*
string_name()620 Output_merge_string<Char_type>::string_name()
621 {
622   gold_unreachable();
623   return NULL;
624 }
625 
626 template<>
627 const char*
string_name()628 Output_merge_string<char>::string_name()
629 {
630   return "strings";
631 }
632 
633 template<>
634 const char*
string_name()635 Output_merge_string<uint16_t>::string_name()
636 {
637   return "16-bit strings";
638 }
639 
640 template<>
641 const char*
string_name()642 Output_merge_string<uint32_t>::string_name()
643 {
644   return "32-bit strings";
645 }
646 
647 // Print merge stats to stderr.
648 
649 template<typename Char_type>
650 void
do_print_merge_stats(const char * section_name)651 Output_merge_string<Char_type>::do_print_merge_stats(const char* section_name)
652 {
653   char buf[200];
654   snprintf(buf, sizeof buf, "%s merged %s", section_name, this->string_name());
655   fprintf(stderr, _("%s: %s input bytes: %zu\n"),
656 	  program_name, buf, this->input_size_);
657   fprintf(stderr, _("%s: %s input strings: %zu\n"),
658 	  program_name, buf, this->input_count_);
659   this->stringpool_.print_stats(buf);
660 }
661 
662 // Instantiate the templates we need.
663 
664 template
665 class Output_merge_string<char>;
666 
667 template
668 class Output_merge_string<uint16_t>;
669 
670 template
671 class Output_merge_string<uint32_t>;
672 
673 #if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
674 template
675 void
676 Object_merge_map::initialize_input_to_output_map<32>(
677     unsigned int shndx,
678     elfcpp::Elf_types<32>::Elf_Addr starting_address,
679     Unordered_map<section_offset_type, elfcpp::Elf_types<32>::Elf_Addr>*);
680 #endif
681 
682 #if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
683 template
684 void
685 Object_merge_map::initialize_input_to_output_map<64>(
686     unsigned int shndx,
687     elfcpp::Elf_types<64>::Elf_Addr starting_address,
688     Unordered_map<section_offset_type, elfcpp::Elf_types<64>::Elf_Addr>*);
689 #endif
690 
691 } // End namespace gold.
692