1/* ELF strtab with GC and suffix merging support.
2   Copyright (C) 2001-2022 Free Software Foundation, Inc.
3   Written by Jakub Jelinek <jakub@redhat.com>.
4
5   This file is part of BFD, the Binary File Descriptor library.
6
7   This program is free software; you can redistribute it and/or modify
8   it under the terms of the GNU General Public License as published by
9   the Free Software Foundation; either version 3 of the License, or
10   (at your option) any later version.
11
12   This program is distributed in the hope that it will be useful,
13   but WITHOUT ANY WARRANTY; without even the implied warranty of
14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15   GNU General Public License for more details.
16
17   You should have received a copy of the GNU General Public License
18   along with this program; if not, write to the Free Software
19   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
20   MA 02110-1301, USA.  */
21
22#include "sysdep.h"
23#include "bfd.h"
24#include "libbfd.h"
25#include "elf-bfd.h"
26#include "hashtab.h"
27#include "libiberty.h"
28
29/* An entry in the strtab hash table.  */
30
31struct elf_strtab_hash_entry
32{
33  struct bfd_hash_entry root;
34  /* Length of this entry.  This includes the zero terminator.  */
35  int len;
36  unsigned int refcount;
37  union {
38    /* Index within the merged section.  */
39    bfd_size_type index;
40    /* Entry this is a suffix of (if len < 0).  */
41    struct elf_strtab_hash_entry *suffix;
42  } u;
43};
44
45/* The strtab hash table.  */
46
47struct elf_strtab_hash
48{
49  struct bfd_hash_table table;
50  /* Next available index.  */
51  size_t size;
52  /* Number of array entries alloced.  */
53  size_t alloced;
54  /* Final strtab size.  */
55  bfd_size_type sec_size;
56  /* Array of pointers to strtab entries.  */
57  struct elf_strtab_hash_entry **array;
58};
59
60/* Routine to create an entry in a section merge hashtab.  */
61
62static struct bfd_hash_entry *
63elf_strtab_hash_newfunc (struct bfd_hash_entry *entry,
64			 struct bfd_hash_table *table,
65			 const char *string)
66{
67  /* Allocate the structure if it has not already been allocated by a
68     subclass.  */
69  if (entry == NULL)
70    entry = (struct bfd_hash_entry *)
71	bfd_hash_allocate (table, sizeof (struct elf_strtab_hash_entry));
72  if (entry == NULL)
73    return NULL;
74
75  /* Call the allocation method of the superclass.  */
76  entry = bfd_hash_newfunc (entry, table, string);
77
78  if (entry)
79    {
80      /* Initialize the local fields.  */
81      struct elf_strtab_hash_entry *ret;
82
83      ret = (struct elf_strtab_hash_entry *) entry;
84      ret->u.index = -1;
85      ret->refcount = 0;
86      ret->len = 0;
87    }
88
89  return entry;
90}
91
92/* Create a new hash table.  */
93
94struct elf_strtab_hash *
95_bfd_elf_strtab_init (void)
96{
97  struct elf_strtab_hash *table;
98  size_t amt = sizeof (struct elf_strtab_hash);
99
100  table = (struct elf_strtab_hash *) bfd_malloc (amt);
101  if (table == NULL)
102    return NULL;
103
104  if (!bfd_hash_table_init (&table->table, elf_strtab_hash_newfunc,
105			    sizeof (struct elf_strtab_hash_entry)))
106    {
107      free (table);
108      return NULL;
109    }
110
111  table->sec_size = 0;
112  table->size = 1;
113  table->alloced = 64;
114  amt = sizeof (struct elf_strtab_hasn_entry *);
115  table->array = ((struct elf_strtab_hash_entry **)
116		  bfd_malloc (table->alloced * amt));
117  if (table->array == NULL)
118    {
119      free (table);
120      return NULL;
121    }
122
123  table->array[0] = NULL;
124
125  return table;
126}
127
128/* Free a strtab.  */
129
130void
131_bfd_elf_strtab_free (struct elf_strtab_hash *tab)
132{
133  bfd_hash_table_free (&tab->table);
134  free (tab->array);
135  free (tab);
136}
137
138/* Get the index of an entity in a hash table, adding it if it is not
139   already present.  */
140
141size_t
142_bfd_elf_strtab_add (struct elf_strtab_hash *tab,
143		     const char *str,
144		     bool copy)
145{
146  register struct elf_strtab_hash_entry *entry;
147
148  /* We handle this specially, since we don't want to do refcounting
149     on it.  */
150  if (*str == '\0')
151    return 0;
152
153  BFD_ASSERT (tab->sec_size == 0);
154  entry = (struct elf_strtab_hash_entry *)
155	  bfd_hash_lookup (&tab->table, str, true, copy);
156
157  if (entry == NULL)
158    return (size_t) -1;
159
160  entry->refcount++;
161  if (entry->len == 0)
162    {
163      entry->len = strlen (str) + 1;
164      /* 2G strings lose.  */
165      BFD_ASSERT (entry->len > 0);
166      if (tab->size == tab->alloced)
167	{
168	  bfd_size_type amt = sizeof (struct elf_strtab_hash_entry *);
169	  tab->alloced *= 2;
170	  tab->array = (struct elf_strtab_hash_entry **)
171	      bfd_realloc_or_free (tab->array, tab->alloced * amt);
172	  if (tab->array == NULL)
173	    return (size_t) -1;
174	}
175
176      entry->u.index = tab->size++;
177      tab->array[entry->u.index] = entry;
178    }
179  return entry->u.index;
180}
181
182void
183_bfd_elf_strtab_addref (struct elf_strtab_hash *tab, size_t idx)
184{
185  if (idx == 0 || idx == (size_t) -1)
186    return;
187  BFD_ASSERT (tab->sec_size == 0);
188  BFD_ASSERT (idx < tab->size);
189  ++tab->array[idx]->refcount;
190}
191
192void
193_bfd_elf_strtab_delref (struct elf_strtab_hash *tab, size_t idx)
194{
195  if (idx == 0 || idx == (size_t) -1)
196    return;
197  BFD_ASSERT (tab->sec_size == 0);
198  BFD_ASSERT (idx < tab->size);
199  BFD_ASSERT (tab->array[idx]->refcount > 0);
200  --tab->array[idx]->refcount;
201}
202
203unsigned int
204_bfd_elf_strtab_refcount (struct elf_strtab_hash *tab, size_t idx)
205{
206  return tab->array[idx]->refcount;
207}
208
209void
210_bfd_elf_strtab_clear_all_refs (struct elf_strtab_hash *tab)
211{
212  size_t idx;
213
214  for (idx = 1; idx < tab->size; idx++)
215    tab->array[idx]->refcount = 0;
216}
217
218/* Save strtab refcounts prior to adding --as-needed library.  */
219
220struct strtab_save
221{
222  size_t size;
223  unsigned int refcount[1];
224};
225
226void *
227_bfd_elf_strtab_save (struct elf_strtab_hash *tab)
228{
229  struct strtab_save *save;
230  size_t idx, size;
231
232  size = sizeof (*save) + (tab->size - 1) * sizeof (save->refcount[0]);
233  save = bfd_malloc (size);
234  if (save == NULL)
235    return save;
236
237  save->size = tab->size;
238  for (idx = 1; idx < tab->size; idx++)
239    save->refcount[idx] = tab->array[idx]->refcount;
240  return save;
241}
242
243/* Restore strtab refcounts on finding --as-needed library not needed.  */
244
245void
246_bfd_elf_strtab_restore (struct elf_strtab_hash *tab, void *buf)
247{
248  size_t idx, curr_size = tab->size, save_size;
249  struct strtab_save *save = (struct strtab_save *) buf;
250
251  BFD_ASSERT (tab->sec_size == 0);
252  save_size = 1;
253  if (save != NULL)
254    save_size = save->size;
255  BFD_ASSERT (save_size <= curr_size);
256  tab->size = save_size;
257  for (idx = 1; idx < save_size; ++idx)
258    tab->array[idx]->refcount = save->refcount[idx];
259
260  for (; idx < curr_size; ++idx)
261    {
262      /* We don't remove entries from the hash table, just set their
263	 REFCOUNT to zero.  Setting LEN zero will result in the size
264	 growing if the entry is added again.  See _bfd_elf_strtab_add.  */
265      tab->array[idx]->refcount = 0;
266      tab->array[idx]->len = 0;
267    }
268}
269
270bfd_size_type
271_bfd_elf_strtab_size (struct elf_strtab_hash *tab)
272{
273  return tab->sec_size ? tab->sec_size : tab->size;
274}
275
276bfd_size_type
277_bfd_elf_strtab_len (struct elf_strtab_hash *tab)
278{
279  return tab->size;
280}
281
282bfd_size_type
283_bfd_elf_strtab_offset (struct elf_strtab_hash *tab, size_t idx)
284{
285  struct elf_strtab_hash_entry *entry;
286
287  if (idx == 0)
288    return 0;
289  BFD_ASSERT (idx < tab->size);
290  BFD_ASSERT (tab->sec_size);
291  entry = tab->array[idx];
292  BFD_ASSERT (entry->refcount > 0);
293  entry->refcount--;
294  return tab->array[idx]->u.index;
295}
296
297const char *
298_bfd_elf_strtab_str (struct elf_strtab_hash *tab, size_t idx,
299		     bfd_size_type *offset)
300{
301  if (idx == 0)
302    return NULL;
303  BFD_ASSERT (idx < tab->size);
304  BFD_ASSERT (tab->sec_size);
305  if (tab->array[idx]->refcount == 0)
306    return NULL;
307  if (offset)
308    *offset = tab->array[idx]->u.index;
309  return tab->array[idx]->root.string;
310}
311
312bool
313_bfd_elf_strtab_emit (register bfd *abfd, struct elf_strtab_hash *tab)
314{
315  bfd_size_type off = 1;
316  size_t i;
317
318  if (bfd_bwrite ("", 1, abfd) != 1)
319    return false;
320
321  for (i = 1; i < tab->size; ++i)
322    {
323      register const char *str;
324      register unsigned int len;
325
326      BFD_ASSERT (tab->array[i]->refcount == 0);
327      len = tab->array[i]->len;
328      if ((int) len < 0)
329	continue;
330
331      str = tab->array[i]->root.string;
332      if (bfd_bwrite (str, len, abfd) != len)
333	return false;
334
335      off += len;
336    }
337
338  BFD_ASSERT (off == tab->sec_size);
339  return true;
340}
341
342/* Compare two elf_strtab_hash_entry structures.  Called via qsort.
343   Won't ever return zero as all entries differ, so there is no issue
344   with qsort stability here.  */
345
346static int
347strrevcmp (const void *a, const void *b)
348{
349  struct elf_strtab_hash_entry *A = *(struct elf_strtab_hash_entry **) a;
350  struct elf_strtab_hash_entry *B = *(struct elf_strtab_hash_entry **) b;
351  unsigned int lenA = A->len;
352  unsigned int lenB = B->len;
353  const unsigned char *s = (const unsigned char *) A->root.string + lenA - 1;
354  const unsigned char *t = (const unsigned char *) B->root.string + lenB - 1;
355  int l = lenA < lenB ? lenA : lenB;
356
357  while (l)
358    {
359      if (*s != *t)
360	return (int) *s - (int) *t;
361      s--;
362      t--;
363      l--;
364    }
365  return lenA - lenB;
366}
367
368static inline int
369is_suffix (const struct elf_strtab_hash_entry *A,
370	   const struct elf_strtab_hash_entry *B)
371{
372  if (A->len <= B->len)
373    /* B cannot be a suffix of A unless A is equal to B, which is guaranteed
374       not to be equal by the hash table.  */
375    return 0;
376
377  return memcmp (A->root.string + (A->len - B->len),
378		 B->root.string, B->len - 1) == 0;
379}
380
381/* This function assigns final string table offsets for used strings,
382   merging strings matching suffixes of longer strings if possible.  */
383
384void
385_bfd_elf_strtab_finalize (struct elf_strtab_hash *tab)
386{
387  struct elf_strtab_hash_entry **array, **a, *e;
388  bfd_size_type amt, sec_size;
389  size_t size, i;
390
391  /* Sort the strings by suffix and length.  */
392  amt = tab->size;
393  amt *= sizeof (struct elf_strtab_hash_entry *);
394  array = (struct elf_strtab_hash_entry **) bfd_malloc (amt);
395  if (array == NULL)
396    goto alloc_failure;
397
398  for (i = 1, a = array; i < tab->size; ++i)
399    {
400      e = tab->array[i];
401      if (e->refcount)
402	{
403	  *a++ = e;
404	  /* Adjust the length to not include the zero terminator.  */
405	  e->len -= 1;
406	}
407      else
408	e->len = 0;
409    }
410
411  size = a - array;
412  if (size != 0)
413    {
414      qsort (array, size, sizeof (struct elf_strtab_hash_entry *), strrevcmp);
415
416      /* Loop over the sorted array and merge suffixes.  Start from the
417	 end because we want eg.
418
419	 s1 -> "d"
420	 s2 -> "bcd"
421	 s3 -> "abcd"
422
423	 to end up as
424
425	 s3 -> "abcd"
426	 s2 _____^
427	 s1 _______^
428
429	 ie. we don't want s1 pointing into the old s2.  */
430      e = *--a;
431      e->len += 1;
432      while (--a >= array)
433	{
434	  struct elf_strtab_hash_entry *cmp = *a;
435
436	  cmp->len += 1;
437	  if (is_suffix (e, cmp))
438	    {
439	      cmp->u.suffix = e;
440	      cmp->len = -cmp->len;
441	    }
442	  else
443	    e = cmp;
444	}
445    }
446
447 alloc_failure:
448  free (array);
449
450  /* Assign positions to the strings we want to keep.  */
451  sec_size = 1;
452  for (i = 1; i < tab->size; ++i)
453    {
454      e = tab->array[i];
455      if (e->refcount && e->len > 0)
456	{
457	  e->u.index = sec_size;
458	  sec_size += e->len;
459	}
460    }
461
462  tab->sec_size = sec_size;
463
464  /* Adjust the rest.  */
465  for (i = 1; i < tab->size; ++i)
466    {
467      e = tab->array[i];
468      if (e->refcount && e->len < 0)
469	e->u.index = e->u.suffix->u.index + (e->u.suffix->len + e->len);
470    }
471}
472