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1/*
2 * elf.c - ELF access library
3 *
4 * Adapted from kpatch (https://github.com/dynup/kpatch):
5 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
6 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version 2
11 * of the License, or (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, see <http://www.gnu.org/licenses/>.
20 */
21
22#include <sys/types.h>
23#include <sys/stat.h>
24#include <fcntl.h>
25#include <stdio.h>
26#include <stdlib.h>
27#include <string.h>
28#include <unistd.h>
29#include <errno.h>
30
31#include "elf.h"
32#include "warn.h"
33
34struct section *find_section_by_name(struct elf *elf, const char *name)
35{
36 struct section *sec;
37
38 list_for_each_entry(sec, &elf->sections, list)
39 if (!strcmp(sec->name, name))
40 return sec;
41
42 return NULL;
43}
44
45static struct section *find_section_by_index(struct elf *elf,
46 unsigned int idx)
47{
48 struct section *sec;
49
50 list_for_each_entry(sec, &elf->sections, list)
51 if (sec->idx == idx)
52 return sec;
53
54 return NULL;
55}
56
57static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
58{
59 struct section *sec;
60 struct symbol *sym;
61
62 list_for_each_entry(sec, &elf->sections, list)
63 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
64 if (sym->idx == idx)
65 return sym;
66
67 return NULL;
68}
69
70struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
71{
72 struct symbol *sym;
73
74 list_for_each_entry(sym, &sec->symbol_list, list)
75 if (sym->type != STT_SECTION &&
76 sym->offset == offset)
77 return sym;
78
79 return NULL;
80}
81
82struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
83{
84 struct section *sec;
85 struct symbol *sym;
86
87 list_for_each_entry(sec, &elf->sections, list)
88 list_for_each_entry(sym, &sec->symbol_list, list)
89 if (!strcmp(sym->name, name))
90 return sym;
91
92 return NULL;
93}
94
95struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
96{
97 struct symbol *sym;
98
99 list_for_each_entry(sym, &sec->symbol_list, list)
100 if (sym->type != STT_SECTION &&
101 offset >= sym->offset && offset < sym->offset + sym->len)
102 return sym;
103
104 return NULL;
105}
106
107struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
108 unsigned int len)
109{
110 struct rela *rela;
111 unsigned long o;
112
113 if (!sec->rela)
114 return NULL;
115
116 for (o = offset; o < offset + len; o++)
117 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
118 if (rela->offset == o)
119 return rela;
120
121 return NULL;
122}
123
124struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
125{
126 return find_rela_by_dest_range(sec, offset, 1);
127}
128
129struct symbol *find_containing_func(struct section *sec, unsigned long offset)
130{
131 struct symbol *func;
132
133 list_for_each_entry(func, &sec->symbol_list, list)
134 if (func->type == STT_FUNC && offset >= func->offset &&
135 offset < func->offset + func->len)
136 return func;
137
138 return NULL;
139}
140
141static int read_sections(struct elf *elf)
142{
143 Elf_Scn *s = NULL;
144 struct section *sec;
145 size_t shstrndx, sections_nr;
146 int i;
147
148 if (elf_getshdrnum(elf->elf, §ions_nr)) {
149 WARN_ELF("elf_getshdrnum");
150 return -1;
151 }
152
153 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
154 WARN_ELF("elf_getshdrstrndx");
155 return -1;
156 }
157
158 for (i = 0; i < sections_nr; i++) {
159 sec = malloc(sizeof(*sec));
160 if (!sec) {
161 perror("malloc");
162 return -1;
163 }
164 memset(sec, 0, sizeof(*sec));
165
166 INIT_LIST_HEAD(&sec->symbol_list);
167 INIT_LIST_HEAD(&sec->rela_list);
168 hash_init(sec->rela_hash);
169 hash_init(sec->symbol_hash);
170
171 list_add_tail(&sec->list, &elf->sections);
172
173 s = elf_getscn(elf->elf, i);
174 if (!s) {
175 WARN_ELF("elf_getscn");
176 return -1;
177 }
178
179 sec->idx = elf_ndxscn(s);
180
181 if (!gelf_getshdr(s, &sec->sh)) {
182 WARN_ELF("gelf_getshdr");
183 return -1;
184 }
185
186 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
187 if (!sec->name) {
188 WARN_ELF("elf_strptr");
189 return -1;
190 }
191
192 if (sec->sh.sh_size != 0) {
193 sec->data = elf_getdata(s, NULL);
194 if (!sec->data) {
195 WARN_ELF("elf_getdata");
196 return -1;
197 }
198 if (sec->data->d_off != 0 ||
199 sec->data->d_size != sec->sh.sh_size) {
200 WARN("unexpected data attributes for %s",
201 sec->name);
202 return -1;
203 }
204 }
205 sec->len = sec->sh.sh_size;
206 }
207
208 /* sanity check, one more call to elf_nextscn() should return NULL */
209 if (elf_nextscn(elf->elf, s)) {
210 WARN("section entry mismatch");
211 return -1;
212 }
213
214 return 0;
215}
216
217static int read_symbols(struct elf *elf)
218{
219 struct section *symtab, *sec;
220 struct symbol *sym, *pfunc;
221 struct list_head *entry, *tmp;
222 int symbols_nr, i;
223 char *coldstr;
224
225 symtab = find_section_by_name(elf, ".symtab");
226 if (!symtab) {
227 WARN("missing symbol table");
228 return -1;
229 }
230
231 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
232
233 for (i = 0; i < symbols_nr; i++) {
234 sym = malloc(sizeof(*sym));
235 if (!sym) {
236 perror("malloc");
237 return -1;
238 }
239 memset(sym, 0, sizeof(*sym));
240
241 sym->idx = i;
242
243 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
244 WARN_ELF("gelf_getsym");
245 goto err;
246 }
247
248 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
249 sym->sym.st_name);
250 if (!sym->name) {
251 WARN_ELF("elf_strptr");
252 goto err;
253 }
254
255 sym->type = GELF_ST_TYPE(sym->sym.st_info);
256 sym->bind = GELF_ST_BIND(sym->sym.st_info);
257
258 if (sym->sym.st_shndx > SHN_UNDEF &&
259 sym->sym.st_shndx < SHN_LORESERVE) {
260 sym->sec = find_section_by_index(elf,
261 sym->sym.st_shndx);
262 if (!sym->sec) {
263 WARN("couldn't find section for symbol %s",
264 sym->name);
265 goto err;
266 }
267 if (sym->type == STT_SECTION) {
268 sym->name = sym->sec->name;
269 sym->sec->sym = sym;
270 }
271 } else
272 sym->sec = find_section_by_index(elf, 0);
273
274 sym->offset = sym->sym.st_value;
275 sym->len = sym->sym.st_size;
276
277 /* sorted insert into a per-section list */
278 entry = &sym->sec->symbol_list;
279 list_for_each_prev(tmp, &sym->sec->symbol_list) {
280 struct symbol *s;
281
282 s = list_entry(tmp, struct symbol, list);
283
284 if (sym->offset > s->offset) {
285 entry = tmp;
286 break;
287 }
288
289 if (sym->offset == s->offset && sym->len >= s->len) {
290 entry = tmp;
291 break;
292 }
293 }
294 list_add(&sym->list, entry);
295 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
296 }
297
298 /* Create parent/child links for any cold subfunctions */
299 list_for_each_entry(sec, &elf->sections, list) {
300 list_for_each_entry(sym, &sec->symbol_list, list) {
301 if (sym->type != STT_FUNC)
302 continue;
303 sym->pfunc = sym->cfunc = sym;
304 coldstr = strstr(sym->name, ".cold.");
305 if (coldstr) {
306 coldstr[0] = '\0';
307 pfunc = find_symbol_by_name(elf, sym->name);
308 coldstr[0] = '.';
309
310 if (!pfunc) {
311 WARN("%s(): can't find parent function",
312 sym->name);
313 goto err;
314 }
315
316 sym->pfunc = pfunc;
317 pfunc->cfunc = sym;
318 }
319 }
320 }
321
322 return 0;
323
324err:
325 free(sym);
326 return -1;
327}
328
329static int read_relas(struct elf *elf)
330{
331 struct section *sec;
332 struct rela *rela;
333 int i;
334 unsigned int symndx;
335
336 list_for_each_entry(sec, &elf->sections, list) {
337 if (sec->sh.sh_type != SHT_RELA)
338 continue;
339
340 sec->base = find_section_by_name(elf, sec->name + 5);
341 if (!sec->base) {
342 WARN("can't find base section for rela section %s",
343 sec->name);
344 return -1;
345 }
346
347 sec->base->rela = sec;
348
349 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
350 rela = malloc(sizeof(*rela));
351 if (!rela) {
352 perror("malloc");
353 return -1;
354 }
355 memset(rela, 0, sizeof(*rela));
356
357 if (!gelf_getrela(sec->data, i, &rela->rela)) {
358 WARN_ELF("gelf_getrela");
359 return -1;
360 }
361
362 rela->type = GELF_R_TYPE(rela->rela.r_info);
363 rela->addend = rela->rela.r_addend;
364 rela->offset = rela->rela.r_offset;
365 symndx = GELF_R_SYM(rela->rela.r_info);
366 rela->sym = find_symbol_by_index(elf, symndx);
367 if (!rela->sym) {
368 WARN("can't find rela entry symbol %d for %s",
369 symndx, sec->name);
370 return -1;
371 }
372
373 list_add_tail(&rela->list, &sec->rela_list);
374 hash_add(sec->rela_hash, &rela->hash, rela->offset);
375
376 }
377 }
378
379 return 0;
380}
381
382struct elf *elf_open(const char *name, int flags)
383{
384 struct elf *elf;
385 Elf_Cmd cmd;
386
387 elf_version(EV_CURRENT);
388
389 elf = malloc(sizeof(*elf));
390 if (!elf) {
391 perror("malloc");
392 return NULL;
393 }
394 memset(elf, 0, sizeof(*elf));
395
396 INIT_LIST_HEAD(&elf->sections);
397
398 elf->fd = open(name, flags);
399 if (elf->fd == -1) {
400 fprintf(stderr, "objtool: Can't open '%s': %s\n",
401 name, strerror(errno));
402 goto err;
403 }
404
405 if ((flags & O_ACCMODE) == O_RDONLY)
406 cmd = ELF_C_READ_MMAP;
407 else if ((flags & O_ACCMODE) == O_RDWR)
408 cmd = ELF_C_RDWR;
409 else /* O_WRONLY */
410 cmd = ELF_C_WRITE;
411
412 elf->elf = elf_begin(elf->fd, cmd, NULL);
413 if (!elf->elf) {
414 WARN_ELF("elf_begin");
415 goto err;
416 }
417
418 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
419 WARN_ELF("gelf_getehdr");
420 goto err;
421 }
422
423 if (read_sections(elf))
424 goto err;
425
426 if (read_symbols(elf))
427 goto err;
428
429 if (read_relas(elf))
430 goto err;
431
432 return elf;
433
434err:
435 elf_close(elf);
436 return NULL;
437}
438
439struct section *elf_create_section(struct elf *elf, const char *name,
440 size_t entsize, int nr)
441{
442 struct section *sec, *shstrtab;
443 size_t size = entsize * nr;
444 struct Elf_Scn *s;
445 Elf_Data *data;
446
447 sec = malloc(sizeof(*sec));
448 if (!sec) {
449 perror("malloc");
450 return NULL;
451 }
452 memset(sec, 0, sizeof(*sec));
453
454 INIT_LIST_HEAD(&sec->symbol_list);
455 INIT_LIST_HEAD(&sec->rela_list);
456 hash_init(sec->rela_hash);
457 hash_init(sec->symbol_hash);
458
459 list_add_tail(&sec->list, &elf->sections);
460
461 s = elf_newscn(elf->elf);
462 if (!s) {
463 WARN_ELF("elf_newscn");
464 return NULL;
465 }
466
467 sec->name = strdup(name);
468 if (!sec->name) {
469 perror("strdup");
470 return NULL;
471 }
472
473 sec->idx = elf_ndxscn(s);
474 sec->len = size;
475 sec->changed = true;
476
477 sec->data = elf_newdata(s);
478 if (!sec->data) {
479 WARN_ELF("elf_newdata");
480 return NULL;
481 }
482
483 sec->data->d_size = size;
484 sec->data->d_align = 1;
485
486 if (size) {
487 sec->data->d_buf = malloc(size);
488 if (!sec->data->d_buf) {
489 perror("malloc");
490 return NULL;
491 }
492 memset(sec->data->d_buf, 0, size);
493 }
494
495 if (!gelf_getshdr(s, &sec->sh)) {
496 WARN_ELF("gelf_getshdr");
497 return NULL;
498 }
499
500 sec->sh.sh_size = size;
501 sec->sh.sh_entsize = entsize;
502 sec->sh.sh_type = SHT_PROGBITS;
503 sec->sh.sh_addralign = 1;
504 sec->sh.sh_flags = SHF_ALLOC;
505
506
507 /* Add section name to .shstrtab */
508 shstrtab = find_section_by_name(elf, ".shstrtab");
509 if (!shstrtab) {
510 WARN("can't find .shstrtab section");
511 return NULL;
512 }
513
514 s = elf_getscn(elf->elf, shstrtab->idx);
515 if (!s) {
516 WARN_ELF("elf_getscn");
517 return NULL;
518 }
519
520 data = elf_newdata(s);
521 if (!data) {
522 WARN_ELF("elf_newdata");
523 return NULL;
524 }
525
526 data->d_buf = sec->name;
527 data->d_size = strlen(name) + 1;
528 data->d_align = 1;
529
530 sec->sh.sh_name = shstrtab->len;
531
532 shstrtab->len += strlen(name) + 1;
533 shstrtab->changed = true;
534
535 return sec;
536}
537
538struct section *elf_create_rela_section(struct elf *elf, struct section *base)
539{
540 char *relaname;
541 struct section *sec;
542
543 relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
544 if (!relaname) {
545 perror("malloc");
546 return NULL;
547 }
548 strcpy(relaname, ".rela");
549 strcat(relaname, base->name);
550
551 sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
552 free(relaname);
553 if (!sec)
554 return NULL;
555
556 base->rela = sec;
557 sec->base = base;
558
559 sec->sh.sh_type = SHT_RELA;
560 sec->sh.sh_addralign = 8;
561 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
562 sec->sh.sh_info = base->idx;
563 sec->sh.sh_flags = SHF_INFO_LINK;
564
565 return sec;
566}
567
568int elf_rebuild_rela_section(struct section *sec)
569{
570 struct rela *rela;
571 int nr, idx = 0, size;
572 GElf_Rela *relas;
573
574 nr = 0;
575 list_for_each_entry(rela, &sec->rela_list, list)
576 nr++;
577
578 size = nr * sizeof(*relas);
579 relas = malloc(size);
580 if (!relas) {
581 perror("malloc");
582 return -1;
583 }
584
585 sec->data->d_buf = relas;
586 sec->data->d_size = size;
587
588 sec->sh.sh_size = size;
589
590 idx = 0;
591 list_for_each_entry(rela, &sec->rela_list, list) {
592 relas[idx].r_offset = rela->offset;
593 relas[idx].r_addend = rela->addend;
594 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
595 idx++;
596 }
597
598 return 0;
599}
600
601int elf_write(struct elf *elf)
602{
603 struct section *sec;
604 Elf_Scn *s;
605
606 /* Update section headers for changed sections: */
607 list_for_each_entry(sec, &elf->sections, list) {
608 if (sec->changed) {
609 s = elf_getscn(elf->elf, sec->idx);
610 if (!s) {
611 WARN_ELF("elf_getscn");
612 return -1;
613 }
614 if (!gelf_update_shdr(s, &sec->sh)) {
615 WARN_ELF("gelf_update_shdr");
616 return -1;
617 }
618 }
619 }
620
621 /* Make sure the new section header entries get updated properly. */
622 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
623
624 /* Write all changes to the file. */
625 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
626 WARN_ELF("elf_update");
627 return -1;
628 }
629
630 return 0;
631}
632
633void elf_close(struct elf *elf)
634{
635 struct section *sec, *tmpsec;
636 struct symbol *sym, *tmpsym;
637 struct rela *rela, *tmprela;
638
639 if (elf->elf)
640 elf_end(elf->elf);
641
642 if (elf->fd > 0)
643 close(elf->fd);
644
645 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
646 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
647 list_del(&sym->list);
648 hash_del(&sym->hash);
649 free(sym);
650 }
651 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
652 list_del(&rela->list);
653 hash_del(&rela->hash);
654 free(rela);
655 }
656 list_del(&sec->list);
657 free(sec);
658 }
659
660 free(elf);
661}