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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * elf.c - ELF access library
4 *
5 * Adapted from kpatch (https://github.com/dynup/kpatch):
6 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
7 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
8 */
9
10#include <sys/types.h>
11#include <sys/stat.h>
12#include <fcntl.h>
13#include <stdio.h>
14#include <stdlib.h>
15#include <string.h>
16#include <unistd.h>
17#include <errno.h>
18
19#include "elf.h"
20#include "warn.h"
21
22#define MAX_NAME_LEN 128
23
24struct section *find_section_by_name(struct elf *elf, const char *name)
25{
26 struct section *sec;
27
28 list_for_each_entry(sec, &elf->sections, list)
29 if (!strcmp(sec->name, name))
30 return sec;
31
32 return NULL;
33}
34
35static struct section *find_section_by_index(struct elf *elf,
36 unsigned int idx)
37{
38 struct section *sec;
39
40 list_for_each_entry(sec, &elf->sections, list)
41 if (sec->idx == idx)
42 return sec;
43
44 return NULL;
45}
46
47static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
48{
49 struct section *sec;
50 struct symbol *sym;
51
52 list_for_each_entry(sec, &elf->sections, list)
53 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
54 if (sym->idx == idx)
55 return sym;
56
57 return NULL;
58}
59
60struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
61{
62 struct symbol *sym;
63
64 list_for_each_entry(sym, &sec->symbol_list, list)
65 if (sym->type != STT_SECTION &&
66 sym->offset == offset)
67 return sym;
68
69 return NULL;
70}
71
72struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
73{
74 struct section *sec;
75 struct symbol *sym;
76
77 list_for_each_entry(sec, &elf->sections, list)
78 list_for_each_entry(sym, &sec->symbol_list, list)
79 if (!strcmp(sym->name, name))
80 return sym;
81
82 return NULL;
83}
84
85struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
86{
87 struct symbol *sym;
88
89 list_for_each_entry(sym, &sec->symbol_list, list)
90 if (sym->type != STT_SECTION &&
91 offset >= sym->offset && offset < sym->offset + sym->len)
92 return sym;
93
94 return NULL;
95}
96
97struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
98 unsigned int len)
99{
100 struct rela *rela;
101 unsigned long o;
102
103 if (!sec->rela)
104 return NULL;
105
106 for (o = offset; o < offset + len; o++)
107 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
108 if (rela->offset == o)
109 return rela;
110
111 return NULL;
112}
113
114struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
115{
116 return find_rela_by_dest_range(sec, offset, 1);
117}
118
119struct symbol *find_containing_func(struct section *sec, unsigned long offset)
120{
121 struct symbol *func;
122
123 list_for_each_entry(func, &sec->symbol_list, list)
124 if (func->type == STT_FUNC && offset >= func->offset &&
125 offset < func->offset + func->len)
126 return func;
127
128 return NULL;
129}
130
131static int read_sections(struct elf *elf)
132{
133 Elf_Scn *s = NULL;
134 struct section *sec;
135 size_t shstrndx, sections_nr;
136 int i;
137
138 if (elf_getshdrnum(elf->elf, §ions_nr)) {
139 WARN_ELF("elf_getshdrnum");
140 return -1;
141 }
142
143 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
144 WARN_ELF("elf_getshdrstrndx");
145 return -1;
146 }
147
148 for (i = 0; i < sections_nr; i++) {
149 sec = malloc(sizeof(*sec));
150 if (!sec) {
151 perror("malloc");
152 return -1;
153 }
154 memset(sec, 0, sizeof(*sec));
155
156 INIT_LIST_HEAD(&sec->symbol_list);
157 INIT_LIST_HEAD(&sec->rela_list);
158 hash_init(sec->rela_hash);
159 hash_init(sec->symbol_hash);
160
161 list_add_tail(&sec->list, &elf->sections);
162
163 s = elf_getscn(elf->elf, i);
164 if (!s) {
165 WARN_ELF("elf_getscn");
166 return -1;
167 }
168
169 sec->idx = elf_ndxscn(s);
170
171 if (!gelf_getshdr(s, &sec->sh)) {
172 WARN_ELF("gelf_getshdr");
173 return -1;
174 }
175
176 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
177 if (!sec->name) {
178 WARN_ELF("elf_strptr");
179 return -1;
180 }
181
182 if (sec->sh.sh_size != 0) {
183 sec->data = elf_getdata(s, NULL);
184 if (!sec->data) {
185 WARN_ELF("elf_getdata");
186 return -1;
187 }
188 if (sec->data->d_off != 0 ||
189 sec->data->d_size != sec->sh.sh_size) {
190 WARN("unexpected data attributes for %s",
191 sec->name);
192 return -1;
193 }
194 }
195 sec->len = sec->sh.sh_size;
196 }
197
198 /* sanity check, one more call to elf_nextscn() should return NULL */
199 if (elf_nextscn(elf->elf, s)) {
200 WARN("section entry mismatch");
201 return -1;
202 }
203
204 return 0;
205}
206
207static int read_symbols(struct elf *elf)
208{
209 struct section *symtab, *sec;
210 struct symbol *sym, *pfunc, *alias;
211 struct list_head *entry, *tmp;
212 int symbols_nr, i;
213 char *coldstr;
214
215 symtab = find_section_by_name(elf, ".symtab");
216 if (!symtab) {
217 WARN("missing symbol table");
218 return -1;
219 }
220
221 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
222
223 for (i = 0; i < symbols_nr; i++) {
224 sym = malloc(sizeof(*sym));
225 if (!sym) {
226 perror("malloc");
227 return -1;
228 }
229 memset(sym, 0, sizeof(*sym));
230 alias = sym;
231
232 sym->idx = i;
233
234 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
235 WARN_ELF("gelf_getsym");
236 goto err;
237 }
238
239 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
240 sym->sym.st_name);
241 if (!sym->name) {
242 WARN_ELF("elf_strptr");
243 goto err;
244 }
245
246 sym->type = GELF_ST_TYPE(sym->sym.st_info);
247 sym->bind = GELF_ST_BIND(sym->sym.st_info);
248
249 if (sym->sym.st_shndx > SHN_UNDEF &&
250 sym->sym.st_shndx < SHN_LORESERVE) {
251 sym->sec = find_section_by_index(elf,
252 sym->sym.st_shndx);
253 if (!sym->sec) {
254 WARN("couldn't find section for symbol %s",
255 sym->name);
256 goto err;
257 }
258 if (sym->type == STT_SECTION) {
259 sym->name = sym->sec->name;
260 sym->sec->sym = sym;
261 }
262 } else
263 sym->sec = find_section_by_index(elf, 0);
264
265 sym->offset = sym->sym.st_value;
266 sym->len = sym->sym.st_size;
267
268 /* sorted insert into a per-section list */
269 entry = &sym->sec->symbol_list;
270 list_for_each_prev(tmp, &sym->sec->symbol_list) {
271 struct symbol *s;
272
273 s = list_entry(tmp, struct symbol, list);
274
275 if (sym->offset > s->offset) {
276 entry = tmp;
277 break;
278 }
279
280 if (sym->offset == s->offset) {
281 if (sym->len && sym->len == s->len && alias == sym)
282 alias = s;
283
284 if (sym->len >= s->len) {
285 entry = tmp;
286 break;
287 }
288 }
289 }
290 sym->alias = alias;
291 list_add(&sym->list, entry);
292 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
293 }
294
295 /* Create parent/child links for any cold subfunctions */
296 list_for_each_entry(sec, &elf->sections, list) {
297 list_for_each_entry(sym, &sec->symbol_list, list) {
298 char pname[MAX_NAME_LEN + 1];
299 size_t pnamelen;
300 if (sym->type != STT_FUNC)
301 continue;
302 sym->pfunc = sym->cfunc = sym;
303 coldstr = strstr(sym->name, ".cold");
304 if (!coldstr)
305 continue;
306
307 pnamelen = coldstr - sym->name;
308 if (pnamelen > MAX_NAME_LEN) {
309 WARN("%s(): parent function name exceeds maximum length of %d characters",
310 sym->name, MAX_NAME_LEN);
311 return -1;
312 }
313
314 strncpy(pname, sym->name, pnamelen);
315 pname[pnamelen] = '\0';
316 pfunc = find_symbol_by_name(elf, pname);
317
318 if (!pfunc) {
319 WARN("%s(): can't find parent function",
320 sym->name);
321 return -1;
322 }
323
324 sym->pfunc = pfunc;
325 pfunc->cfunc = sym;
326
327 /*
328 * Unfortunately, -fnoreorder-functions puts the child
329 * inside the parent. Remove the overlap so we can
330 * have sane assumptions.
331 *
332 * Note that pfunc->len now no longer matches
333 * pfunc->sym.st_size.
334 */
335 if (sym->sec == pfunc->sec &&
336 sym->offset >= pfunc->offset &&
337 sym->offset + sym->len == pfunc->offset + pfunc->len) {
338 pfunc->len -= sym->len;
339 }
340 }
341 }
342
343 return 0;
344
345err:
346 free(sym);
347 return -1;
348}
349
350static int read_relas(struct elf *elf)
351{
352 struct section *sec;
353 struct rela *rela;
354 int i;
355 unsigned int symndx;
356
357 list_for_each_entry(sec, &elf->sections, list) {
358 if (sec->sh.sh_type != SHT_RELA)
359 continue;
360
361 sec->base = find_section_by_name(elf, sec->name + 5);
362 if (!sec->base) {
363 WARN("can't find base section for rela section %s",
364 sec->name);
365 return -1;
366 }
367
368 sec->base->rela = sec;
369
370 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
371 rela = malloc(sizeof(*rela));
372 if (!rela) {
373 perror("malloc");
374 return -1;
375 }
376 memset(rela, 0, sizeof(*rela));
377
378 if (!gelf_getrela(sec->data, i, &rela->rela)) {
379 WARN_ELF("gelf_getrela");
380 return -1;
381 }
382
383 rela->type = GELF_R_TYPE(rela->rela.r_info);
384 rela->addend = rela->rela.r_addend;
385 rela->offset = rela->rela.r_offset;
386 symndx = GELF_R_SYM(rela->rela.r_info);
387 rela->sym = find_symbol_by_index(elf, symndx);
388 rela->sec = sec;
389 if (!rela->sym) {
390 WARN("can't find rela entry symbol %d for %s",
391 symndx, sec->name);
392 return -1;
393 }
394
395 list_add_tail(&rela->list, &sec->rela_list);
396 hash_add(sec->rela_hash, &rela->hash, rela->offset);
397
398 }
399 }
400
401 return 0;
402}
403
404struct elf *elf_read(const char *name, int flags)
405{
406 struct elf *elf;
407 Elf_Cmd cmd;
408
409 elf_version(EV_CURRENT);
410
411 elf = malloc(sizeof(*elf));
412 if (!elf) {
413 perror("malloc");
414 return NULL;
415 }
416 memset(elf, 0, sizeof(*elf));
417
418 INIT_LIST_HEAD(&elf->sections);
419
420 elf->fd = open(name, flags);
421 if (elf->fd == -1) {
422 fprintf(stderr, "objtool: Can't open '%s': %s\n",
423 name, strerror(errno));
424 goto err;
425 }
426
427 if ((flags & O_ACCMODE) == O_RDONLY)
428 cmd = ELF_C_READ_MMAP;
429 else if ((flags & O_ACCMODE) == O_RDWR)
430 cmd = ELF_C_RDWR;
431 else /* O_WRONLY */
432 cmd = ELF_C_WRITE;
433
434 elf->elf = elf_begin(elf->fd, cmd, NULL);
435 if (!elf->elf) {
436 WARN_ELF("elf_begin");
437 goto err;
438 }
439
440 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
441 WARN_ELF("gelf_getehdr");
442 goto err;
443 }
444
445 if (read_sections(elf))
446 goto err;
447
448 if (read_symbols(elf))
449 goto err;
450
451 if (read_relas(elf))
452 goto err;
453
454 return elf;
455
456err:
457 elf_close(elf);
458 return NULL;
459}
460
461struct section *elf_create_section(struct elf *elf, const char *name,
462 size_t entsize, int nr)
463{
464 struct section *sec, *shstrtab;
465 size_t size = entsize * nr;
466 Elf_Scn *s;
467 Elf_Data *data;
468
469 sec = malloc(sizeof(*sec));
470 if (!sec) {
471 perror("malloc");
472 return NULL;
473 }
474 memset(sec, 0, sizeof(*sec));
475
476 INIT_LIST_HEAD(&sec->symbol_list);
477 INIT_LIST_HEAD(&sec->rela_list);
478 hash_init(sec->rela_hash);
479 hash_init(sec->symbol_hash);
480
481 list_add_tail(&sec->list, &elf->sections);
482
483 s = elf_newscn(elf->elf);
484 if (!s) {
485 WARN_ELF("elf_newscn");
486 return NULL;
487 }
488
489 sec->name = strdup(name);
490 if (!sec->name) {
491 perror("strdup");
492 return NULL;
493 }
494
495 sec->idx = elf_ndxscn(s);
496 sec->len = size;
497 sec->changed = true;
498
499 sec->data = elf_newdata(s);
500 if (!sec->data) {
501 WARN_ELF("elf_newdata");
502 return NULL;
503 }
504
505 sec->data->d_size = size;
506 sec->data->d_align = 1;
507
508 if (size) {
509 sec->data->d_buf = malloc(size);
510 if (!sec->data->d_buf) {
511 perror("malloc");
512 return NULL;
513 }
514 memset(sec->data->d_buf, 0, size);
515 }
516
517 if (!gelf_getshdr(s, &sec->sh)) {
518 WARN_ELF("gelf_getshdr");
519 return NULL;
520 }
521
522 sec->sh.sh_size = size;
523 sec->sh.sh_entsize = entsize;
524 sec->sh.sh_type = SHT_PROGBITS;
525 sec->sh.sh_addralign = 1;
526 sec->sh.sh_flags = SHF_ALLOC;
527
528
529 /* Add section name to .shstrtab (or .strtab for Clang) */
530 shstrtab = find_section_by_name(elf, ".shstrtab");
531 if (!shstrtab)
532 shstrtab = find_section_by_name(elf, ".strtab");
533 if (!shstrtab) {
534 WARN("can't find .shstrtab or .strtab section");
535 return NULL;
536 }
537
538 s = elf_getscn(elf->elf, shstrtab->idx);
539 if (!s) {
540 WARN_ELF("elf_getscn");
541 return NULL;
542 }
543
544 data = elf_newdata(s);
545 if (!data) {
546 WARN_ELF("elf_newdata");
547 return NULL;
548 }
549
550 data->d_buf = sec->name;
551 data->d_size = strlen(name) + 1;
552 data->d_align = 1;
553
554 sec->sh.sh_name = shstrtab->len;
555
556 shstrtab->len += strlen(name) + 1;
557 shstrtab->changed = true;
558
559 return sec;
560}
561
562struct section *elf_create_rela_section(struct elf *elf, struct section *base)
563{
564 char *relaname;
565 struct section *sec;
566
567 relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
568 if (!relaname) {
569 perror("malloc");
570 return NULL;
571 }
572 strcpy(relaname, ".rela");
573 strcat(relaname, base->name);
574
575 sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
576 free(relaname);
577 if (!sec)
578 return NULL;
579
580 base->rela = sec;
581 sec->base = base;
582
583 sec->sh.sh_type = SHT_RELA;
584 sec->sh.sh_addralign = 8;
585 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
586 sec->sh.sh_info = base->idx;
587 sec->sh.sh_flags = SHF_INFO_LINK;
588
589 return sec;
590}
591
592int elf_rebuild_rela_section(struct section *sec)
593{
594 struct rela *rela;
595 int nr, idx = 0, size;
596 GElf_Rela *relas;
597
598 nr = 0;
599 list_for_each_entry(rela, &sec->rela_list, list)
600 nr++;
601
602 size = nr * sizeof(*relas);
603 relas = malloc(size);
604 if (!relas) {
605 perror("malloc");
606 return -1;
607 }
608
609 sec->data->d_buf = relas;
610 sec->data->d_size = size;
611
612 sec->sh.sh_size = size;
613
614 idx = 0;
615 list_for_each_entry(rela, &sec->rela_list, list) {
616 relas[idx].r_offset = rela->offset;
617 relas[idx].r_addend = rela->addend;
618 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
619 idx++;
620 }
621
622 return 0;
623}
624
625int elf_write(struct elf *elf)
626{
627 struct section *sec;
628 Elf_Scn *s;
629
630 /* Update section headers for changed sections: */
631 list_for_each_entry(sec, &elf->sections, list) {
632 if (sec->changed) {
633 s = elf_getscn(elf->elf, sec->idx);
634 if (!s) {
635 WARN_ELF("elf_getscn");
636 return -1;
637 }
638 if (!gelf_update_shdr(s, &sec->sh)) {
639 WARN_ELF("gelf_update_shdr");
640 return -1;
641 }
642 }
643 }
644
645 /* Make sure the new section header entries get updated properly. */
646 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
647
648 /* Write all changes to the file. */
649 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
650 WARN_ELF("elf_update");
651 return -1;
652 }
653
654 return 0;
655}
656
657void elf_close(struct elf *elf)
658{
659 struct section *sec, *tmpsec;
660 struct symbol *sym, *tmpsym;
661 struct rela *rela, *tmprela;
662
663 if (elf->elf)
664 elf_end(elf->elf);
665
666 if (elf->fd > 0)
667 close(elf->fd);
668
669 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
670 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
671 list_del(&sym->list);
672 hash_del(&sym->hash);
673 free(sym);
674 }
675 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
676 list_del(&rela->list);
677 hash_del(&rela->hash);
678 free(rela);
679 }
680 list_del(&sec->list);
681 free(sec);
682 }
683
684 free(elf);
685}