1 // stringpool.cc -- a string pool 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 <cstring>
26 #include <algorithm>
27 #include <vector>
28 
29 #include "output.h"
30 #include "parameters.h"
31 #include "stringpool.h"
32 
33 namespace gold
34 {
35 
36 template<typename Stringpool_char>
Stringpool_template(uint64_t addralign)37 Stringpool_template<Stringpool_char>::Stringpool_template(uint64_t addralign)
38   : string_set_(), key_to_offset_(), strings_(), strtab_size_(0),
39     zero_null_(true), optimize_(false), offset_(sizeof(Stringpool_char)),
40     addralign_(addralign)
41 {
42   if (parameters->options_valid()
43       && parameters->options().optimize() >= 2
44       && addralign <= sizeof(Stringpool_char))
45     this->optimize_ = true;
46 }
47 
48 template<typename Stringpool_char>
49 void
clear()50 Stringpool_template<Stringpool_char>::clear()
51 {
52   for (typename std::list<Stringdata*>::iterator p = this->strings_.begin();
53        p != this->strings_.end();
54        ++p)
55     delete[] reinterpret_cast<char*>(*p);
56   this->strings_.clear();
57   this->key_to_offset_.clear();
58   this->string_set_.clear();
59 }
60 
61 template<typename Stringpool_char>
~Stringpool_template()62 Stringpool_template<Stringpool_char>::~Stringpool_template()
63 {
64   this->clear();
65 }
66 
67 // Resize the internal hashtable with the expectation we'll get n new
68 // elements.  Note that the hashtable constructor takes a "number of
69 // buckets you'd like," rather than "number of elements you'd like,"
70 // but that's the best we can do.
71 
72 template<typename Stringpool_char>
73 void
reserve(unsigned int n)74 Stringpool_template<Stringpool_char>::reserve(unsigned int n)
75 {
76   this->key_to_offset_.reserve(n);
77 
78 #if defined(HAVE_UNORDERED_MAP)
79   this->string_set_.rehash(this->string_set_.size() + n);
80   return;
81 #elif defined(HAVE_TR1_UNORDERED_MAP)
82   // rehash() implementation is broken in gcc 4.0.3's stl
83   //this->string_set_.rehash(this->string_set_.size() + n);
84   //return;
85 #elif defined(HAVE_EXT_HASH_MAP)
86   this->string_set_.resize(this->string_set_.size() + n);
87   return;
88 #endif
89 
90   // This is the generic "reserve" code, if no #ifdef above triggers.
91   String_set_type new_string_set(this->string_set_.size() + n);
92   new_string_set.insert(this->string_set_.begin(), this->string_set_.end());
93   this->string_set_.swap(new_string_set);
94 }
95 
96 // Compare two strings of arbitrary character type for equality.
97 
98 template<typename Stringpool_char>
99 bool
string_equal(const Stringpool_char * s1,const Stringpool_char * s2)100 Stringpool_template<Stringpool_char>::string_equal(const Stringpool_char* s1,
101 						   const Stringpool_char* s2)
102 {
103   while (*s1 != 0)
104     if (*s1++ != *s2++)
105       return false;
106   return *s2 == 0;
107 }
108 
109 // Specialize string_equal for char.
110 
111 template<>
112 inline bool
string_equal(const char * s1,const char * s2)113 Stringpool_template<char>::string_equal(const char* s1, const char* s2)
114 {
115   return strcmp(s1, s2) == 0;
116 }
117 
118 // Equality comparison function for the hash table.
119 
120 template<typename Stringpool_char>
121 inline bool
operator ()(const Hashkey & h1,const Hashkey & h2) const122 Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
123     const Hashkey& h1,
124     const Hashkey& h2) const
125 {
126   return (h1.hash_code == h2.hash_code
127 	  && h1.length == h2.length
128 	  && (h1.string == h2.string
129 	      || memcmp(h1.string, h2.string,
130 			h1.length * sizeof(Stringpool_char)) == 0));
131 }
132 
133 // Hash function.  The length is in characters, not bytes.
134 
135 template<typename Stringpool_char>
136 size_t
string_hash(const Stringpool_char * s,size_t length)137 Stringpool_template<Stringpool_char>::string_hash(const Stringpool_char* s,
138 						  size_t length)
139 {
140   return gold::string_hash<Stringpool_char>(s, length);
141 }
142 
143 // Add the string S to the list of canonical strings.  Return a
144 // pointer to the canonical string.  If PKEY is not NULL, set *PKEY to
145 // the key.  LENGTH is the length of S in characters.  Note that S may
146 // not be NUL terminated.
147 
148 template<typename Stringpool_char>
149 const Stringpool_char*
add_string(const Stringpool_char * s,size_t len)150 Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
151 						 size_t len)
152 {
153   // We are in trouble if we've already computed the string offsets.
154   gold_assert(this->strtab_size_ == 0);
155 
156   // The size we allocate for a new Stringdata.
157   const size_t buffer_size = 1000;
158   // The amount we multiply the Stringdata index when calculating the
159   // key.
160   const size_t key_mult = 1024;
161   gold_assert(key_mult >= buffer_size);
162 
163   // Convert len to the number of bytes we need to allocate, including
164   // the null character.
165   len = (len + 1) * sizeof(Stringpool_char);
166 
167   size_t alc;
168   bool front = true;
169   if (len > buffer_size)
170     {
171       alc = sizeof(Stringdata) + len;
172       front = false;
173     }
174   else if (this->strings_.empty())
175     alc = sizeof(Stringdata) + buffer_size;
176   else
177     {
178       Stringdata* psd = this->strings_.front();
179       if (len > psd->alc - psd->len)
180 	alc = sizeof(Stringdata) + buffer_size;
181       else
182 	{
183 	  char* ret = psd->data + psd->len;
184 	  memcpy(ret, s, len - sizeof(Stringpool_char));
185 	  memset(ret + len - sizeof(Stringpool_char), 0,
186 		 sizeof(Stringpool_char));
187 
188 	  psd->len += len;
189 
190 	  return reinterpret_cast<const Stringpool_char*>(ret);
191 	}
192     }
193 
194   Stringdata* psd = reinterpret_cast<Stringdata*>(new char[alc]);
195   psd->alc = alc - sizeof(Stringdata);
196   memcpy(psd->data, s, len - sizeof(Stringpool_char));
197   memset(psd->data + len - sizeof(Stringpool_char), 0,
198 	 sizeof(Stringpool_char));
199   psd->len = len;
200 
201   if (front)
202     this->strings_.push_front(psd);
203   else
204     this->strings_.push_back(psd);
205 
206   return reinterpret_cast<const Stringpool_char*>(psd->data);
207 }
208 
209 // Add a string to a string pool.
210 
211 template<typename Stringpool_char>
212 const Stringpool_char*
add(const Stringpool_char * s,bool copy,Key * pkey)213 Stringpool_template<Stringpool_char>::add(const Stringpool_char* s, bool copy,
214                                           Key* pkey)
215 {
216   return this->add_with_length(s, string_length(s), copy, pkey);
217 }
218 
219 // Add a new key offset entry.
220 
221 template<typename Stringpool_char>
222 void
new_key_offset(size_t length)223 Stringpool_template<Stringpool_char>::new_key_offset(size_t length)
224 {
225   section_offset_type offset;
226   if (this->zero_null_ && length == 0)
227     offset = 0;
228   else
229     {
230       offset = this->offset_;
231       // Align strings.
232       offset = align_address(offset, this->addralign_);
233       this->offset_ = offset + (length + 1) * sizeof(Stringpool_char);
234     }
235   this->key_to_offset_.push_back(offset);
236 }
237 
238 template<typename Stringpool_char>
239 const Stringpool_char*
add_with_length(const Stringpool_char * s,size_t length,bool copy,Key * pkey)240 Stringpool_template<Stringpool_char>::add_with_length(const Stringpool_char* s,
241 						      size_t length,
242 						      bool copy,
243 						      Key* pkey)
244 {
245   typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
246 
247   // We add 1 so that 0 is always invalid.
248   const Key k = this->key_to_offset_.size() + 1;
249 
250   if (!copy)
251     {
252       // When we don't need to copy the string, we can call insert
253       // directly.
254 
255       std::pair<Hashkey, Hashval> element(Hashkey(s, length), k);
256 
257       Insert_type ins = this->string_set_.insert(element);
258 
259       typename String_set_type::const_iterator p = ins.first;
260 
261       if (ins.second)
262 	{
263 	  // We just added the string.  The key value has now been
264 	  // used.
265 	  this->new_key_offset(length);
266 	}
267       else
268 	{
269 	  gold_assert(k != p->second);
270 	}
271 
272       if (pkey != NULL)
273 	*pkey = p->second;
274       return p->first.string;
275     }
276 
277   // When we have to copy the string, we look it up twice in the hash
278   // table.  The problem is that we can't insert S before we
279   // canonicalize it by copying it into the canonical list. The hash
280   // code will only be computed once.
281 
282   Hashkey hk(s, length);
283   typename String_set_type::const_iterator p = this->string_set_.find(hk);
284   if (p != this->string_set_.end())
285     {
286       if (pkey != NULL)
287 	*pkey = p->second;
288       return p->first.string;
289     }
290 
291   this->new_key_offset(length);
292 
293   hk.string = this->add_string(s, length);
294   // The contents of the string stay the same, so we don't need to
295   // adjust hk.hash_code or hk.length.
296 
297   std::pair<Hashkey, Hashval> element(hk, k);
298 
299   Insert_type ins = this->string_set_.insert(element);
300   gold_assert(ins.second);
301 
302   if (pkey != NULL)
303     *pkey = k;
304   return hk.string;
305 }
306 
307 template<typename Stringpool_char>
308 const Stringpool_char*
find(const Stringpool_char * s,Key * pkey) const309 Stringpool_template<Stringpool_char>::find(const Stringpool_char* s,
310 					   Key* pkey) const
311 {
312   Hashkey hk(s);
313   typename String_set_type::const_iterator p = this->string_set_.find(hk);
314   if (p == this->string_set_.end())
315     return NULL;
316 
317   if (pkey != NULL)
318     *pkey = p->second;
319 
320   return p->first.string;
321 }
322 
323 // Comparison routine used when sorting into an ELF strtab.  We want
324 // to sort this so that when one string is a suffix of another, we
325 // always see the shorter string immediately after the longer string.
326 // For example, we want to see these strings in this order:
327 //   abcd
328 //   cd
329 //   d
330 // When strings are not suffixes, we don't care what order they are
331 // in, but we need to ensure that suffixes wind up next to each other.
332 // So we do a reversed lexicographic sort on the reversed string.
333 
334 template<typename Stringpool_char>
335 bool
operator ()(const Stringpool_sort_info & sort_info1,const Stringpool_sort_info & sort_info2) const336 Stringpool_template<Stringpool_char>::Stringpool_sort_comparison::operator()(
337   const Stringpool_sort_info& sort_info1,
338   const Stringpool_sort_info& sort_info2) const
339 {
340   const Hashkey& h1(sort_info1->first);
341   const Hashkey& h2(sort_info2->first);
342   const Stringpool_char* s1 = h1.string;
343   const Stringpool_char* s2 = h2.string;
344   const size_t len1 = h1.length;
345   const size_t len2 = h2.length;
346   const size_t minlen = len1 < len2 ? len1 : len2;
347   const Stringpool_char* p1 = s1 + len1 - 1;
348   const Stringpool_char* p2 = s2 + len2 - 1;
349   for (size_t i = minlen; i > 0; --i, --p1, --p2)
350     {
351       if (*p1 != *p2)
352 	return *p1 > *p2;
353     }
354   return len1 > len2;
355 }
356 
357 // Return whether s1 is a suffix of s2.
358 
359 template<typename Stringpool_char>
360 bool
is_suffix(const Stringpool_char * s1,size_t len1,const Stringpool_char * s2,size_t len2)361 Stringpool_template<Stringpool_char>::is_suffix(const Stringpool_char* s1,
362                                                 size_t len1,
363 						const Stringpool_char* s2,
364                                                 size_t len2)
365 {
366   if (len1 > len2)
367     return false;
368   return memcmp(s1, s2 + len2 - len1, len1 * sizeof(Stringpool_char)) == 0;
369 }
370 
371 // Turn the stringpool into an ELF strtab: determine the offsets of
372 // each string in the table.
373 
374 template<typename Stringpool_char>
375 void
set_string_offsets()376 Stringpool_template<Stringpool_char>::set_string_offsets()
377 {
378   if (this->strtab_size_ != 0)
379     {
380       // We've already computed the offsets.
381       return;
382     }
383 
384   const size_t charsize = sizeof(Stringpool_char);
385 
386   // Offset 0 may be reserved for the empty string.
387   section_offset_type offset = this->zero_null_ ? charsize : 0;
388 
389   // Sorting to find suffixes can take over 25% of the total CPU time
390   // used by the linker.  Since it's merely an optimization to reduce
391   // the strtab size, and gives a relatively small benefit (it's
392   // typically rare for a symbol to be a suffix of another), we only
393   // take the time to sort when the user asks for heavy optimization.
394   if (!this->optimize_)
395     {
396       // If we are not optimizing, the offsets are already assigned.
397       offset = this->offset_;
398     }
399   else
400     {
401       size_t count = this->string_set_.size();
402 
403       std::vector<Stringpool_sort_info> v;
404       v.reserve(count);
405 
406       for (typename String_set_type::iterator p = this->string_set_.begin();
407            p != this->string_set_.end();
408            ++p)
409         v.push_back(Stringpool_sort_info(p));
410 
411       std::sort(v.begin(), v.end(), Stringpool_sort_comparison());
412 
413       section_offset_type last_offset = -1;
414       for (typename std::vector<Stringpool_sort_info>::iterator last = v.end(),
415              curr = v.begin();
416            curr != v.end();
417            last = curr++)
418         {
419 	  section_offset_type this_offset;
420           if (this->zero_null_ && (*curr)->first.string[0] == 0)
421             this_offset = 0;
422           else if (last != v.end()
423                    && ((((*curr)->first.length - (*last)->first.length)
424 			% this->addralign_) == 0)
425                    && is_suffix((*curr)->first.string,
426 				(*curr)->first.length,
427                                 (*last)->first.string,
428 				(*last)->first.length))
429             this_offset = (last_offset
430 			   + (((*last)->first.length - (*curr)->first.length)
431 			      * charsize));
432           else
433             {
434               this_offset = align_address(offset, this->addralign_);
435               offset = this_offset + ((*curr)->first.length + 1) * charsize;
436             }
437 	  this->key_to_offset_[(*curr)->second - 1] = this_offset;
438 	  last_offset = this_offset;
439         }
440     }
441 
442   this->strtab_size_ = offset;
443 }
444 
445 // Get the offset of a string in the ELF strtab.  The string must
446 // exist.
447 
448 template<typename Stringpool_char>
449 section_offset_type
get_offset(const Stringpool_char * s) const450 Stringpool_template<Stringpool_char>::get_offset(const Stringpool_char* s)
451   const
452 {
453   return this->get_offset_with_length(s, string_length(s));
454 }
455 
456 template<typename Stringpool_char>
457 section_offset_type
get_offset_with_length(const Stringpool_char * s,size_t length) const458 Stringpool_template<Stringpool_char>::get_offset_with_length(
459     const Stringpool_char* s,
460     size_t length) const
461 {
462   gold_assert(this->strtab_size_ != 0);
463   Hashkey hk(s, length);
464   typename String_set_type::const_iterator p = this->string_set_.find(hk);
465   if (p != this->string_set_.end())
466     return this->key_to_offset_[p->second - 1];
467   gold_unreachable();
468 }
469 
470 // Write the ELF strtab into the buffer.
471 
472 template<typename Stringpool_char>
473 void
write_to_buffer(unsigned char * buffer,section_size_type bufsize)474 Stringpool_template<Stringpool_char>::write_to_buffer(
475     unsigned char* buffer,
476     section_size_type bufsize)
477 {
478   gold_assert(this->strtab_size_ != 0);
479   gold_assert(bufsize >= this->strtab_size_);
480   if (this->zero_null_)
481     buffer[0] = '\0';
482   for (typename String_set_type::const_iterator p = this->string_set_.begin();
483        p != this->string_set_.end();
484        ++p)
485     {
486       const int len = (p->first.length + 1) * sizeof(Stringpool_char);
487       const section_offset_type offset = this->key_to_offset_[p->second - 1];
488       gold_assert(static_cast<section_size_type>(offset) + len
489 		  <= this->strtab_size_);
490       memcpy(buffer + offset, p->first.string, len);
491     }
492 }
493 
494 // Write the ELF strtab into the output file at the specified offset.
495 
496 template<typename Stringpool_char>
497 void
write(Output_file * of,off_t offset)498 Stringpool_template<Stringpool_char>::write(Output_file* of, off_t offset)
499 {
500   gold_assert(this->strtab_size_ != 0);
501   unsigned char* view = of->get_output_view(offset, this->strtab_size_);
502   this->write_to_buffer(view, this->strtab_size_);
503   of->write_output_view(offset, this->strtab_size_, view);
504 }
505 
506 // Print statistical information to stderr.  This is used for --stats.
507 
508 template<typename Stringpool_char>
509 void
print_stats(const char * name) const510 Stringpool_template<Stringpool_char>::print_stats(const char* name) const
511 {
512 #if defined(HAVE_UNORDERED_MAP) || defined(HAVE_TR1_UNORDERED_MAP) || defined(HAVE_EXT_HASH_MAP)
513   fprintf(stderr, _("%s: %s entries: %zu; buckets: %zu\n"),
514 	  program_name, name, this->string_set_.size(),
515 	  this->string_set_.bucket_count());
516 #else
517   fprintf(stderr, _("%s: %s entries: %zu\n"),
518 	  program_name, name, this->table_.size());
519 #endif
520   fprintf(stderr, _("%s: %s Stringdata structures: %zu\n"),
521 	  program_name, name, this->strings_.size());
522 }
523 
524 // Instantiate the templates we need.
525 
526 template
527 class Stringpool_template<char>;
528 
529 template
530 class Stringpool_template<uint16_t>;
531 
532 template
533 class Stringpool_template<uint32_t>;
534 
535 } // End namespace gold.
536