1/* ELF/DWARF string table handling.
2   Copyright (C) 2000, 2001, 2002, 2005, 2016 Red Hat, Inc.
3   This file is part of elfutils.
4   Written by Ulrich Drepper <drepper@redhat.com>, 2000.
5
6   This file is free software; you can redistribute it and/or modify
7   it under the terms of either
8
9     * the GNU Lesser General Public License as published by the Free
10       Software Foundation; either version 3 of the License, or (at
11       your option) any later version
12
13   or
14
15     * the GNU General Public License as published by the Free
16       Software Foundation; either version 2 of the License, or (at
17       your option) any later version
18
19   or both in parallel, as here.
20
21   elfutils is distributed in the hope that it will be useful, but
22   WITHOUT ANY WARRANTY; without even the implied warranty of
23   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
24   General Public License for more details.
25
26   You should have received copies of the GNU General Public License and
27   the GNU Lesser General Public License along with this program.  If
28   not, see <http://www.gnu.org/licenses/>.  */
29
30#ifdef HAVE_CONFIG_H
31# include <config.h>
32#endif
33
34#include <assert.h>
35#include <inttypes.h>
36#include <libelf.h>
37#include <stddef.h>
38#include <stdlib.h>
39#include <string.h>
40
41#include "libdwelfP.h"
42#include <system.h>
43
44
45struct Dwelf_Strent
46{
47  const char *string;
48  size_t len;
49  struct Dwelf_Strent *next;
50  struct Dwelf_Strent *left;
51  struct Dwelf_Strent *right;
52  size_t offset;
53  char reverse[0];
54};
55
56
57struct memoryblock
58{
59  struct memoryblock *next;
60  char memory[0];
61};
62
63
64struct Dwelf_Strtab
65{
66  struct Dwelf_Strent *root;
67  struct memoryblock *memory;
68  char *backp;
69  size_t left;
70  size_t total;
71  bool nullstr;
72
73  struct Dwelf_Strent null;
74};
75
76
77/* Cache for the pagesize.  */
78static size_t ps;
79/* We correct this value a bit so that `malloc' is not allocating more
80   than a page. */
81#define MALLOC_OVERHEAD (2 * sizeof (void *))
82
83
84Dwelf_Strtab *
85dwelf_strtab_init (bool nullstr)
86{
87  if (ps == 0)
88    {
89      ps = sysconf (_SC_PAGESIZE);
90      assert (sizeof (struct memoryblock) < ps - MALLOC_OVERHEAD);
91    }
92
93  Dwelf_Strtab *ret = calloc (1, sizeof (struct Dwelf_Strtab));
94  if (ret != NULL)
95    {
96      ret->nullstr = nullstr;
97
98      if (nullstr)
99	{
100	  ret->null.len = 1;
101	  ret->null.string = "";
102	}
103    }
104
105  return ret;
106}
107
108
109static int
110morememory (Dwelf_Strtab *st, size_t len)
111{
112  size_t overhead = offsetof (struct memoryblock, memory);
113  len += overhead + MALLOC_OVERHEAD;
114
115  /* Allocate nearest multiple of pagesize >= len.  */
116  len = ((len / ps) + (len % ps != 0)) * ps - MALLOC_OVERHEAD;
117
118  struct memoryblock *newmem = malloc (len);
119  if (newmem == NULL)
120    return 1;
121
122  newmem->next = st->memory;
123  st->memory = newmem;
124  st->backp = newmem->memory;
125  st->left = len - overhead;
126
127  return 0;
128}
129
130
131void
132dwelf_strtab_free (Dwelf_Strtab *st)
133{
134  struct memoryblock *mb = st->memory;
135
136  while (mb != NULL)
137    {
138      void *old = mb;
139      mb = mb->next;
140      free (old);
141    }
142
143  free (st);
144}
145
146
147static Dwelf_Strent *
148newstring (Dwelf_Strtab *st, const char *str, size_t len)
149{
150  /* Compute the amount of padding needed to make the structure aligned.  */
151  size_t align = ((__alignof__ (struct Dwelf_Strent)
152		   - (((uintptr_t) st->backp)
153		      & (__alignof__ (struct Dwelf_Strent) - 1)))
154		  & (__alignof__ (struct Dwelf_Strent) - 1));
155
156  /* Make sure there is enough room in the memory block.  */
157  if (st->left < align + sizeof (struct Dwelf_Strent) + len)
158    {
159      if (morememory (st, sizeof (struct Dwelf_Strent) + len))
160	return NULL;
161
162      align = 0;
163    }
164
165  /* Create the reserved string.  */
166  Dwelf_Strent *newstr = (Dwelf_Strent *) (st->backp + align);
167  newstr->string = str;
168  newstr->len = len;
169  newstr->next = NULL;
170  newstr->left = NULL;
171  newstr->right = NULL;
172  newstr->offset = 0;
173  for (int i = len - 2; i >= 0; --i)
174    newstr->reverse[i] = str[len - 2 - i];
175  newstr->reverse[len - 1] = '\0';
176  st->backp += align + sizeof (struct Dwelf_Strent) + len;
177  st->left -= align + sizeof (struct Dwelf_Strent) + len;
178
179  return newstr;
180}
181
182
183/* XXX This function should definitely be rewritten to use a balancing
184   tree algorithm (AVL, red-black trees).  For now a simple, correct
185   implementation is enough.  */
186static Dwelf_Strent **
187searchstring (Dwelf_Strent **sep, Dwelf_Strent *newstr)
188{
189  /* More strings?  */
190  if (*sep == NULL)
191    {
192      *sep = newstr;
193      return sep;
194    }
195
196  /* Compare the strings.  */
197  int cmpres = memcmp ((*sep)->reverse, newstr->reverse,
198		       MIN ((*sep)->len, newstr->len) - 1);
199  if (cmpres == 0)
200    /* We found a matching string.  */
201    return sep;
202  else if (cmpres > 0)
203    return searchstring (&(*sep)->left, newstr);
204  else
205    return searchstring (&(*sep)->right, newstr);
206}
207
208
209/* Add new string.  The actual string is assumed to be permanent.  */
210static Dwelf_Strent *
211strtab_add (Dwelf_Strtab *st, const char *str, size_t len)
212{
213  /* Make sure all "" strings get offset 0 but only if the table was
214     created with a special null entry in mind.  */
215  if (len == 1 && st->null.string != NULL)
216    return &st->null;
217
218  /* Allocate memory for the new string and its associated information.  */
219  Dwelf_Strent *newstr = newstring (st, str, len);
220  if (newstr == NULL)
221    return NULL;
222
223  /* Search in the array for the place to insert the string.  If there
224     is no string with matching prefix and no string with matching
225     leading substring, create a new entry.  */
226  Dwelf_Strent **sep = searchstring (&st->root, newstr);
227  if (*sep != newstr)
228    {
229      /* This is not the same entry.  This means we have a prefix match.  */
230      if ((*sep)->len > newstr->len)
231	{
232	  /* Check whether we already know this string.  */
233	  for (Dwelf_Strent *subs = (*sep)->next; subs != NULL;
234	       subs = subs->next)
235	    if (subs->len == newstr->len)
236	      {
237		/* We have an exact match with a substring.  Free the memory
238		   we allocated.  */
239		st->left += st->backp - (char *) newstr;
240		st->backp = (char *) newstr;
241
242		return subs;
243	      }
244
245	  /* We have a new substring.  This means we don't need the reverse
246	     string of this entry anymore.  */
247	  st->backp -= newstr->len;
248	  st->left += newstr->len;
249
250	  newstr->next = (*sep)->next;
251	  (*sep)->next = newstr;
252	}
253      else if ((*sep)->len != newstr->len)
254	{
255	  /* When we get here it means that the string we are about to
256	     add has a common prefix with a string we already have but
257	     it is longer.  In this case we have to put it first.  */
258	  st->total += newstr->len - (*sep)->len;
259	  newstr->next = *sep;
260	  newstr->left = (*sep)->left;
261	  newstr->right = (*sep)->right;
262	  *sep = newstr;
263	}
264      else
265	{
266	  /* We have an exact match.  Free the memory we allocated.  */
267	  st->left += st->backp - (char *) newstr;
268	  st->backp = (char *) newstr;
269
270	  newstr = *sep;
271	}
272    }
273  else
274    st->total += newstr->len;
275
276  return newstr;
277}
278
279Dwelf_Strent *
280dwelf_strtab_add (Dwelf_Strtab *st, const char *str)
281{
282  return strtab_add (st, str, strlen (str) + 1);
283}
284
285Dwelf_Strent *
286dwelf_strtab_add_len (Dwelf_Strtab *st, const char *str, size_t len)
287{
288  return strtab_add (st, str, len);
289}
290
291static void
292copystrings (Dwelf_Strent *nodep, char **freep, size_t *offsetp)
293{
294  if (nodep->left != NULL)
295    copystrings (nodep->left, freep, offsetp);
296
297  /* Process the current node.  */
298  nodep->offset = *offsetp;
299  *freep = (char *) mempcpy (*freep, nodep->string, nodep->len);
300  *offsetp += nodep->len;
301
302  for (Dwelf_Strent *subs = nodep->next; subs != NULL; subs = subs->next)
303    {
304      assert (subs->len < nodep->len);
305      subs->offset = nodep->offset + nodep->len - subs->len;
306      assert (subs->offset != 0 || subs->string[0] == '\0');
307    }
308
309  if (nodep->right != NULL)
310    copystrings (nodep->right, freep, offsetp);
311}
312
313
314Elf_Data *
315dwelf_strtab_finalize (Dwelf_Strtab *st, Elf_Data *data)
316{
317  size_t nulllen = st->nullstr ? 1 : 0;
318
319  /* Fill in the information.  */
320  data->d_buf = malloc (st->total + nulllen);
321  if (data->d_buf == NULL)
322    return NULL;
323
324  /* The first byte must always be zero if we created the table with a
325     null string.  */
326  if (st->nullstr)
327    *((char *) data->d_buf) = '\0';
328
329  data->d_type = ELF_T_BYTE;
330  data->d_size = st->total + nulllen;
331  data->d_off = 0;
332  data->d_align = 1;
333  data->d_version = EV_CURRENT;
334
335  /* Now run through the tree and add all the string while also updating
336     the offset members of the elfstrent records.  */
337  char *endp = (char *) data->d_buf + nulllen;
338  size_t copylen = nulllen;
339  if (st->root)
340    copystrings (st->root, &endp, &copylen);
341  assert (copylen == st->total + nulllen);
342
343  return data;
344}
345
346
347size_t
348dwelf_strent_off (Dwelf_Strent *se)
349{
350  return se->offset;
351}
352
353
354const char *
355dwelf_strent_str (Dwelf_Strent *se)
356{
357  return se->string;
358}
359