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 <sys/mman.h>
13 #include <fcntl.h>
14 #include <stdio.h>
15 #include <stdlib.h>
16 #include <string.h>
17 #include <unistd.h>
18 #include <errno.h>
19 #include <objtool/builtin.h>
20
21 #include <objtool/elf.h>
22 #include <objtool/warn.h>
23
24 #define MAX_NAME_LEN 128
25
str_hash(const char * str)26 static inline u32 str_hash(const char *str)
27 {
28 return jhash(str, strlen(str), 0);
29 }
30
31 #define __elf_table(name) (elf->name##_hash)
32 #define __elf_bits(name) (elf->name##_bits)
33
34 #define elf_hash_add(name, node, key) \
35 hlist_add_head(node, &__elf_table(name)[hash_min(key, __elf_bits(name))])
36
37 #define elf_hash_for_each_possible(name, obj, member, key) \
38 hlist_for_each_entry(obj, &__elf_table(name)[hash_min(key, __elf_bits(name))], member)
39
40 #define elf_alloc_hash(name, size) \
41 ({ \
42 __elf_bits(name) = max(10, ilog2(size)); \
43 __elf_table(name) = mmap(NULL, sizeof(struct hlist_head) << __elf_bits(name), \
44 PROT_READ|PROT_WRITE, \
45 MAP_PRIVATE|MAP_ANON, -1, 0); \
46 if (__elf_table(name) == (void *)-1L) { \
47 WARN("mmap fail " #name); \
48 __elf_table(name) = NULL; \
49 } \
50 __elf_table(name); \
51 })
52
symbol_to_offset(struct rb_node * a,const struct rb_node * b)53 static bool symbol_to_offset(struct rb_node *a, const struct rb_node *b)
54 {
55 struct symbol *sa = rb_entry(a, struct symbol, node);
56 struct symbol *sb = rb_entry(b, struct symbol, node);
57
58 if (sa->offset < sb->offset)
59 return true;
60 if (sa->offset > sb->offset)
61 return false;
62
63 if (sa->len < sb->len)
64 return true;
65 if (sa->len > sb->len)
66 return false;
67
68 sa->alias = sb;
69
70 return false;
71 }
72
symbol_by_offset(const void * key,const struct rb_node * node)73 static int symbol_by_offset(const void *key, const struct rb_node *node)
74 {
75 const struct symbol *s = rb_entry(node, struct symbol, node);
76 const unsigned long *o = key;
77
78 if (*o < s->offset)
79 return -1;
80 if (*o >= s->offset + s->len)
81 return 1;
82
83 return 0;
84 }
85
find_section_by_name(const struct elf * elf,const char * name)86 struct section *find_section_by_name(const struct elf *elf, const char *name)
87 {
88 struct section *sec;
89
90 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
91 if (!strcmp(sec->name, name))
92 return sec;
93 }
94
95 return NULL;
96 }
97
find_section_by_index(struct elf * elf,unsigned int idx)98 static struct section *find_section_by_index(struct elf *elf,
99 unsigned int idx)
100 {
101 struct section *sec;
102
103 elf_hash_for_each_possible(section, sec, hash, idx) {
104 if (sec->idx == idx)
105 return sec;
106 }
107
108 return NULL;
109 }
110
find_symbol_by_index(struct elf * elf,unsigned int idx)111 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
112 {
113 struct symbol *sym;
114
115 elf_hash_for_each_possible(symbol, sym, hash, idx) {
116 if (sym->idx == idx)
117 return sym;
118 }
119
120 return NULL;
121 }
122
find_symbol_by_offset(struct section * sec,unsigned long offset)123 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
124 {
125 struct rb_node *node;
126
127 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
128 struct symbol *s = rb_entry(node, struct symbol, node);
129
130 if (s->offset == offset && s->type != STT_SECTION)
131 return s;
132 }
133
134 return NULL;
135 }
136
find_func_by_offset(struct section * sec,unsigned long offset)137 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
138 {
139 struct rb_node *node;
140
141 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
142 struct symbol *s = rb_entry(node, struct symbol, node);
143
144 if (s->offset == offset && s->type == STT_FUNC)
145 return s;
146 }
147
148 return NULL;
149 }
150
find_symbol_containing(const struct section * sec,unsigned long offset)151 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
152 {
153 struct rb_node *node;
154
155 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
156 struct symbol *s = rb_entry(node, struct symbol, node);
157
158 if (s->type != STT_SECTION)
159 return s;
160 }
161
162 return NULL;
163 }
164
find_func_containing(struct section * sec,unsigned long offset)165 struct symbol *find_func_containing(struct section *sec, unsigned long offset)
166 {
167 struct rb_node *node;
168
169 rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
170 struct symbol *s = rb_entry(node, struct symbol, node);
171
172 if (s->type == STT_FUNC)
173 return s;
174 }
175
176 return NULL;
177 }
178
find_symbol_by_name(const struct elf * elf,const char * name)179 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
180 {
181 struct symbol *sym;
182
183 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
184 if (!strcmp(sym->name, name))
185 return sym;
186 }
187
188 return NULL;
189 }
190
find_reloc_by_dest_range(const struct elf * elf,struct section * sec,unsigned long offset,unsigned int len)191 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
192 unsigned long offset, unsigned int len)
193 {
194 struct reloc *reloc, *r = NULL;
195 unsigned long o;
196
197 if (!sec->reloc)
198 return NULL;
199
200 sec = sec->reloc;
201
202 for_offset_range(o, offset, offset + len) {
203 elf_hash_for_each_possible(reloc, reloc, hash,
204 sec_offset_hash(sec, o)) {
205 if (reloc->sec != sec)
206 continue;
207
208 if (reloc->offset >= offset && reloc->offset < offset + len) {
209 if (!r || reloc->offset < r->offset)
210 r = reloc;
211 }
212 }
213 if (r)
214 return r;
215 }
216
217 return NULL;
218 }
219
find_reloc_by_dest(const struct elf * elf,struct section * sec,unsigned long offset)220 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
221 {
222 return find_reloc_by_dest_range(elf, sec, offset, 1);
223 }
224
read_sections(struct elf * elf)225 static int read_sections(struct elf *elf)
226 {
227 Elf_Scn *s = NULL;
228 struct section *sec;
229 size_t shstrndx, sections_nr;
230 int i;
231
232 if (elf_getshdrnum(elf->elf, §ions_nr)) {
233 WARN_ELF("elf_getshdrnum");
234 return -1;
235 }
236
237 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
238 WARN_ELF("elf_getshdrstrndx");
239 return -1;
240 }
241
242 if (!elf_alloc_hash(section, sections_nr) ||
243 !elf_alloc_hash(section_name, sections_nr))
244 return -1;
245
246 for (i = 0; i < sections_nr; i++) {
247 sec = malloc(sizeof(*sec));
248 if (!sec) {
249 perror("malloc");
250 return -1;
251 }
252 memset(sec, 0, sizeof(*sec));
253
254 INIT_LIST_HEAD(&sec->symbol_list);
255 INIT_LIST_HEAD(&sec->reloc_list);
256
257 s = elf_getscn(elf->elf, i);
258 if (!s) {
259 WARN_ELF("elf_getscn");
260 return -1;
261 }
262
263 sec->idx = elf_ndxscn(s);
264
265 if (!gelf_getshdr(s, &sec->sh)) {
266 WARN_ELF("gelf_getshdr");
267 return -1;
268 }
269
270 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
271 if (!sec->name) {
272 WARN_ELF("elf_strptr");
273 return -1;
274 }
275
276 if (sec->sh.sh_size != 0) {
277 sec->data = elf_getdata(s, NULL);
278 if (!sec->data) {
279 WARN_ELF("elf_getdata");
280 return -1;
281 }
282 if (sec->data->d_off != 0 ||
283 sec->data->d_size != sec->sh.sh_size) {
284 WARN("unexpected data attributes for %s",
285 sec->name);
286 return -1;
287 }
288 }
289
290 if (sec->sh.sh_flags & SHF_EXECINSTR)
291 elf->text_size += sec->sh.sh_size;
292
293 list_add_tail(&sec->list, &elf->sections);
294 elf_hash_add(section, &sec->hash, sec->idx);
295 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
296 }
297
298 if (stats) {
299 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
300 printf("section_bits: %d\n", elf->section_bits);
301 }
302
303 /* sanity check, one more call to elf_nextscn() should return NULL */
304 if (elf_nextscn(elf->elf, s)) {
305 WARN("section entry mismatch");
306 return -1;
307 }
308
309 return 0;
310 }
311
elf_add_symbol(struct elf * elf,struct symbol * sym)312 static void elf_add_symbol(struct elf *elf, struct symbol *sym)
313 {
314 struct list_head *entry;
315 struct rb_node *pnode;
316
317 sym->type = GELF_ST_TYPE(sym->sym.st_info);
318 sym->bind = GELF_ST_BIND(sym->sym.st_info);
319
320 sym->offset = sym->sym.st_value;
321 sym->len = sym->sym.st_size;
322
323 rb_add(&sym->node, &sym->sec->symbol_tree, symbol_to_offset);
324 pnode = rb_prev(&sym->node);
325 if (pnode)
326 entry = &rb_entry(pnode, struct symbol, node)->list;
327 else
328 entry = &sym->sec->symbol_list;
329 list_add(&sym->list, entry);
330 elf_hash_add(symbol, &sym->hash, sym->idx);
331 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
332
333 /*
334 * Don't store empty STT_NOTYPE symbols in the rbtree. They
335 * can exist within a function, confusing the sorting.
336 */
337 if (!sym->len)
338 rb_erase(&sym->node, &sym->sec->symbol_tree);
339 }
340
read_symbols(struct elf * elf)341 static int read_symbols(struct elf *elf)
342 {
343 struct section *symtab, *symtab_shndx, *sec;
344 struct symbol *sym, *pfunc;
345 int symbols_nr, i;
346 char *coldstr;
347 Elf_Data *shndx_data = NULL;
348 Elf32_Word shndx;
349
350 symtab = find_section_by_name(elf, ".symtab");
351 if (symtab) {
352 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
353 if (symtab_shndx)
354 shndx_data = symtab_shndx->data;
355
356 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
357 } else {
358 /*
359 * A missing symbol table is actually possible if it's an empty
360 * .o file. This can happen for thunk_64.o. Make sure to at
361 * least allocate the symbol hash tables so we can do symbol
362 * lookups without crashing.
363 */
364 symbols_nr = 0;
365 }
366
367 if (!elf_alloc_hash(symbol, symbols_nr) ||
368 !elf_alloc_hash(symbol_name, symbols_nr))
369 return -1;
370
371 for (i = 0; i < symbols_nr; i++) {
372 sym = malloc(sizeof(*sym));
373 if (!sym) {
374 perror("malloc");
375 return -1;
376 }
377 memset(sym, 0, sizeof(*sym));
378 sym->alias = sym;
379
380 sym->idx = i;
381
382 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
383 &shndx)) {
384 WARN_ELF("gelf_getsymshndx");
385 goto err;
386 }
387
388 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
389 sym->sym.st_name);
390 if (!sym->name) {
391 WARN_ELF("elf_strptr");
392 goto err;
393 }
394
395 if ((sym->sym.st_shndx > SHN_UNDEF &&
396 sym->sym.st_shndx < SHN_LORESERVE) ||
397 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
398 if (sym->sym.st_shndx != SHN_XINDEX)
399 shndx = sym->sym.st_shndx;
400
401 sym->sec = find_section_by_index(elf, shndx);
402 if (!sym->sec) {
403 WARN("couldn't find section for symbol %s",
404 sym->name);
405 goto err;
406 }
407 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
408 sym->name = sym->sec->name;
409 sym->sec->sym = sym;
410 }
411 } else
412 sym->sec = find_section_by_index(elf, 0);
413
414 elf_add_symbol(elf, sym);
415 }
416
417 if (stats) {
418 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
419 printf("symbol_bits: %d\n", elf->symbol_bits);
420 }
421
422 /* Create parent/child links for any cold subfunctions */
423 list_for_each_entry(sec, &elf->sections, list) {
424 list_for_each_entry(sym, &sec->symbol_list, list) {
425 char pname[MAX_NAME_LEN + 1];
426 size_t pnamelen;
427 if (sym->type != STT_FUNC)
428 continue;
429
430 if (sym->pfunc == NULL)
431 sym->pfunc = sym;
432
433 if (sym->cfunc == NULL)
434 sym->cfunc = sym;
435
436 coldstr = strstr(sym->name, ".cold");
437 if (!coldstr)
438 continue;
439
440 pnamelen = coldstr - sym->name;
441 if (pnamelen > MAX_NAME_LEN) {
442 WARN("%s(): parent function name exceeds maximum length of %d characters",
443 sym->name, MAX_NAME_LEN);
444 return -1;
445 }
446
447 strncpy(pname, sym->name, pnamelen);
448 pname[pnamelen] = '\0';
449 pfunc = find_symbol_by_name(elf, pname);
450
451 if (!pfunc) {
452 WARN("%s(): can't find parent function",
453 sym->name);
454 return -1;
455 }
456
457 sym->pfunc = pfunc;
458 pfunc->cfunc = sym;
459
460 /*
461 * Unfortunately, -fnoreorder-functions puts the child
462 * inside the parent. Remove the overlap so we can
463 * have sane assumptions.
464 *
465 * Note that pfunc->len now no longer matches
466 * pfunc->sym.st_size.
467 */
468 if (sym->sec == pfunc->sec &&
469 sym->offset >= pfunc->offset &&
470 sym->offset + sym->len == pfunc->offset + pfunc->len) {
471 pfunc->len -= sym->len;
472 }
473 }
474 }
475
476 return 0;
477
478 err:
479 free(sym);
480 return -1;
481 }
482
483 static struct section *elf_create_reloc_section(struct elf *elf,
484 struct section *base,
485 int reltype);
486
elf_add_reloc(struct elf * elf,struct section * sec,unsigned long offset,unsigned int type,struct symbol * sym,int addend)487 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
488 unsigned int type, struct symbol *sym, int addend)
489 {
490 struct reloc *reloc;
491
492 if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
493 return -1;
494
495 reloc = malloc(sizeof(*reloc));
496 if (!reloc) {
497 perror("malloc");
498 return -1;
499 }
500 memset(reloc, 0, sizeof(*reloc));
501
502 reloc->sec = sec->reloc;
503 reloc->offset = offset;
504 reloc->type = type;
505 reloc->sym = sym;
506 reloc->addend = addend;
507
508 list_add_tail(&reloc->list, &sec->reloc->reloc_list);
509 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
510
511 sec->reloc->sh.sh_size += sec->reloc->sh.sh_entsize;
512 sec->reloc->changed = true;
513
514 return 0;
515 }
516
elf_add_reloc_to_insn(struct elf * elf,struct section * sec,unsigned long offset,unsigned int type,struct section * insn_sec,unsigned long insn_off)517 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
518 unsigned long offset, unsigned int type,
519 struct section *insn_sec, unsigned long insn_off)
520 {
521 struct symbol *sym;
522 int addend;
523
524 if (insn_sec->sym) {
525 sym = insn_sec->sym;
526 addend = insn_off;
527
528 } else {
529 /*
530 * The Clang assembler strips section symbols, so we have to
531 * reference the function symbol instead:
532 */
533 sym = find_symbol_containing(insn_sec, insn_off);
534 if (!sym) {
535 /*
536 * Hack alert. This happens when we need to reference
537 * the NOP pad insn immediately after the function.
538 */
539 sym = find_symbol_containing(insn_sec, insn_off - 1);
540 }
541
542 if (!sym) {
543 WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off);
544 return -1;
545 }
546
547 addend = insn_off - sym->offset;
548 }
549
550 return elf_add_reloc(elf, sec, offset, type, sym, addend);
551 }
552
read_rel_reloc(struct section * sec,int i,struct reloc * reloc,unsigned int * symndx)553 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
554 {
555 if (!gelf_getrel(sec->data, i, &reloc->rel)) {
556 WARN_ELF("gelf_getrel");
557 return -1;
558 }
559 reloc->type = GELF_R_TYPE(reloc->rel.r_info);
560 reloc->addend = 0;
561 reloc->offset = reloc->rel.r_offset;
562 *symndx = GELF_R_SYM(reloc->rel.r_info);
563 return 0;
564 }
565
read_rela_reloc(struct section * sec,int i,struct reloc * reloc,unsigned int * symndx)566 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
567 {
568 if (!gelf_getrela(sec->data, i, &reloc->rela)) {
569 WARN_ELF("gelf_getrela");
570 return -1;
571 }
572 reloc->type = GELF_R_TYPE(reloc->rela.r_info);
573 reloc->addend = reloc->rela.r_addend;
574 reloc->offset = reloc->rela.r_offset;
575 *symndx = GELF_R_SYM(reloc->rela.r_info);
576 return 0;
577 }
578
read_relocs(struct elf * elf)579 static int read_relocs(struct elf *elf)
580 {
581 struct section *sec;
582 struct reloc *reloc;
583 int i;
584 unsigned int symndx;
585 unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
586
587 if (!elf_alloc_hash(reloc, elf->text_size / 16))
588 return -1;
589
590 list_for_each_entry(sec, &elf->sections, list) {
591 if ((sec->sh.sh_type != SHT_RELA) &&
592 (sec->sh.sh_type != SHT_REL))
593 continue;
594
595 sec->base = find_section_by_index(elf, sec->sh.sh_info);
596 if (!sec->base) {
597 WARN("can't find base section for reloc section %s",
598 sec->name);
599 return -1;
600 }
601
602 sec->base->reloc = sec;
603
604 nr_reloc = 0;
605 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
606 reloc = malloc(sizeof(*reloc));
607 if (!reloc) {
608 perror("malloc");
609 return -1;
610 }
611 memset(reloc, 0, sizeof(*reloc));
612 switch (sec->sh.sh_type) {
613 case SHT_REL:
614 if (read_rel_reloc(sec, i, reloc, &symndx))
615 return -1;
616 break;
617 case SHT_RELA:
618 if (read_rela_reloc(sec, i, reloc, &symndx))
619 return -1;
620 break;
621 default: return -1;
622 }
623
624 reloc->sec = sec;
625 reloc->idx = i;
626 reloc->sym = find_symbol_by_index(elf, symndx);
627 if (!reloc->sym) {
628 WARN("can't find reloc entry symbol %d for %s",
629 symndx, sec->name);
630 return -1;
631 }
632
633 list_add_tail(&reloc->list, &sec->reloc_list);
634 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
635
636 nr_reloc++;
637 }
638 max_reloc = max(max_reloc, nr_reloc);
639 tot_reloc += nr_reloc;
640 }
641
642 if (stats) {
643 printf("max_reloc: %lu\n", max_reloc);
644 printf("tot_reloc: %lu\n", tot_reloc);
645 printf("reloc_bits: %d\n", elf->reloc_bits);
646 }
647
648 return 0;
649 }
650
elf_open_read(const char * name,int flags)651 struct elf *elf_open_read(const char *name, int flags)
652 {
653 struct elf *elf;
654 Elf_Cmd cmd;
655
656 elf_version(EV_CURRENT);
657
658 elf = malloc(sizeof(*elf));
659 if (!elf) {
660 perror("malloc");
661 return NULL;
662 }
663 memset(elf, 0, offsetof(struct elf, sections));
664
665 INIT_LIST_HEAD(&elf->sections);
666
667 elf->fd = open(name, flags);
668 if (elf->fd == -1) {
669 fprintf(stderr, "objtool: Can't open '%s': %s\n",
670 name, strerror(errno));
671 goto err;
672 }
673
674 if ((flags & O_ACCMODE) == O_RDONLY)
675 cmd = ELF_C_READ_MMAP;
676 else if ((flags & O_ACCMODE) == O_RDWR)
677 cmd = ELF_C_RDWR;
678 else /* O_WRONLY */
679 cmd = ELF_C_WRITE;
680
681 elf->elf = elf_begin(elf->fd, cmd, NULL);
682 if (!elf->elf) {
683 WARN_ELF("elf_begin");
684 goto err;
685 }
686
687 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
688 WARN_ELF("gelf_getehdr");
689 goto err;
690 }
691
692 if (read_sections(elf))
693 goto err;
694
695 if (read_symbols(elf))
696 goto err;
697
698 if (read_relocs(elf))
699 goto err;
700
701 return elf;
702
703 err:
704 elf_close(elf);
705 return NULL;
706 }
707
elf_add_string(struct elf * elf,struct section * strtab,char * str)708 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
709 {
710 Elf_Data *data;
711 Elf_Scn *s;
712 int len;
713
714 if (!strtab)
715 strtab = find_section_by_name(elf, ".strtab");
716 if (!strtab) {
717 WARN("can't find .strtab section");
718 return -1;
719 }
720
721 s = elf_getscn(elf->elf, strtab->idx);
722 if (!s) {
723 WARN_ELF("elf_getscn");
724 return -1;
725 }
726
727 data = elf_newdata(s);
728 if (!data) {
729 WARN_ELF("elf_newdata");
730 return -1;
731 }
732
733 data->d_buf = str;
734 data->d_size = strlen(str) + 1;
735 data->d_align = 1;
736
737 len = strtab->sh.sh_size;
738 strtab->sh.sh_size += data->d_size;
739 strtab->changed = true;
740
741 return len;
742 }
743
elf_create_undef_symbol(struct elf * elf,const char * name)744 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
745 {
746 struct section *symtab, *symtab_shndx;
747 struct symbol *sym;
748 Elf_Data *data;
749 Elf_Scn *s;
750
751 sym = malloc(sizeof(*sym));
752 if (!sym) {
753 perror("malloc");
754 return NULL;
755 }
756 memset(sym, 0, sizeof(*sym));
757
758 sym->name = strdup(name);
759
760 sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
761 if (sym->sym.st_name == -1)
762 return NULL;
763
764 sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
765 // st_other 0
766 // st_shndx 0
767 // st_value 0
768 // st_size 0
769
770 symtab = find_section_by_name(elf, ".symtab");
771 if (!symtab) {
772 WARN("can't find .symtab");
773 return NULL;
774 }
775
776 s = elf_getscn(elf->elf, symtab->idx);
777 if (!s) {
778 WARN_ELF("elf_getscn");
779 return NULL;
780 }
781
782 data = elf_newdata(s);
783 if (!data) {
784 WARN_ELF("elf_newdata");
785 return NULL;
786 }
787
788 data->d_buf = &sym->sym;
789 data->d_size = sizeof(sym->sym);
790 data->d_align = 1;
791 data->d_type = ELF_T_SYM;
792
793 sym->idx = symtab->sh.sh_size / sizeof(sym->sym);
794
795 symtab->sh.sh_size += data->d_size;
796 symtab->changed = true;
797
798 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
799 if (symtab_shndx) {
800 s = elf_getscn(elf->elf, symtab_shndx->idx);
801 if (!s) {
802 WARN_ELF("elf_getscn");
803 return NULL;
804 }
805
806 data = elf_newdata(s);
807 if (!data) {
808 WARN_ELF("elf_newdata");
809 return NULL;
810 }
811
812 data->d_buf = &sym->sym.st_size; /* conveniently 0 */
813 data->d_size = sizeof(Elf32_Word);
814 data->d_align = 4;
815 data->d_type = ELF_T_WORD;
816
817 symtab_shndx->sh.sh_size += 4;
818 symtab_shndx->changed = true;
819 }
820
821 sym->sec = find_section_by_index(elf, 0);
822
823 elf_add_symbol(elf, sym);
824
825 return sym;
826 }
827
elf_create_section(struct elf * elf,const char * name,unsigned int sh_flags,size_t entsize,int nr)828 struct section *elf_create_section(struct elf *elf, const char *name,
829 unsigned int sh_flags, size_t entsize, int nr)
830 {
831 struct section *sec, *shstrtab;
832 size_t size = entsize * nr;
833 Elf_Scn *s;
834
835 sec = malloc(sizeof(*sec));
836 if (!sec) {
837 perror("malloc");
838 return NULL;
839 }
840 memset(sec, 0, sizeof(*sec));
841
842 INIT_LIST_HEAD(&sec->symbol_list);
843 INIT_LIST_HEAD(&sec->reloc_list);
844
845 s = elf_newscn(elf->elf);
846 if (!s) {
847 WARN_ELF("elf_newscn");
848 return NULL;
849 }
850
851 sec->name = strdup(name);
852 if (!sec->name) {
853 perror("strdup");
854 return NULL;
855 }
856
857 sec->idx = elf_ndxscn(s);
858 sec->changed = true;
859
860 sec->data = elf_newdata(s);
861 if (!sec->data) {
862 WARN_ELF("elf_newdata");
863 return NULL;
864 }
865
866 sec->data->d_size = size;
867 sec->data->d_align = 1;
868
869 if (size) {
870 sec->data->d_buf = malloc(size);
871 if (!sec->data->d_buf) {
872 perror("malloc");
873 return NULL;
874 }
875 memset(sec->data->d_buf, 0, size);
876 }
877
878 if (!gelf_getshdr(s, &sec->sh)) {
879 WARN_ELF("gelf_getshdr");
880 return NULL;
881 }
882
883 sec->sh.sh_size = size;
884 sec->sh.sh_entsize = entsize;
885 sec->sh.sh_type = SHT_PROGBITS;
886 sec->sh.sh_addralign = 1;
887 sec->sh.sh_flags = SHF_ALLOC | sh_flags;
888
889 /* Add section name to .shstrtab (or .strtab for Clang) */
890 shstrtab = find_section_by_name(elf, ".shstrtab");
891 if (!shstrtab)
892 shstrtab = find_section_by_name(elf, ".strtab");
893 if (!shstrtab) {
894 WARN("can't find .shstrtab or .strtab section");
895 return NULL;
896 }
897 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
898 if (sec->sh.sh_name == -1)
899 return NULL;
900
901 list_add_tail(&sec->list, &elf->sections);
902 elf_hash_add(section, &sec->hash, sec->idx);
903 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
904
905 elf->changed = true;
906
907 return sec;
908 }
909
elf_create_rel_reloc_section(struct elf * elf,struct section * base)910 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
911 {
912 char *relocname;
913 struct section *sec;
914
915 relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
916 if (!relocname) {
917 perror("malloc");
918 return NULL;
919 }
920 strcpy(relocname, ".rel");
921 strcat(relocname, base->name);
922
923 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
924 free(relocname);
925 if (!sec)
926 return NULL;
927
928 base->reloc = sec;
929 sec->base = base;
930
931 sec->sh.sh_type = SHT_REL;
932 sec->sh.sh_addralign = 8;
933 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
934 sec->sh.sh_info = base->idx;
935 sec->sh.sh_flags = SHF_INFO_LINK;
936
937 return sec;
938 }
939
elf_create_rela_reloc_section(struct elf * elf,struct section * base)940 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
941 {
942 char *relocname;
943 struct section *sec;
944
945 relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
946 if (!relocname) {
947 perror("malloc");
948 return NULL;
949 }
950 strcpy(relocname, ".rela");
951 strcat(relocname, base->name);
952
953 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
954 free(relocname);
955 if (!sec)
956 return NULL;
957
958 base->reloc = sec;
959 sec->base = base;
960
961 sec->sh.sh_type = SHT_RELA;
962 sec->sh.sh_addralign = 8;
963 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
964 sec->sh.sh_info = base->idx;
965 sec->sh.sh_flags = SHF_INFO_LINK;
966
967 return sec;
968 }
969
elf_create_reloc_section(struct elf * elf,struct section * base,int reltype)970 static struct section *elf_create_reloc_section(struct elf *elf,
971 struct section *base,
972 int reltype)
973 {
974 switch (reltype) {
975 case SHT_REL: return elf_create_rel_reloc_section(elf, base);
976 case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
977 default: return NULL;
978 }
979 }
980
elf_rebuild_rel_reloc_section(struct section * sec)981 static int elf_rebuild_rel_reloc_section(struct section *sec)
982 {
983 struct reloc *reloc;
984 int idx = 0;
985 void *buf;
986
987 /* Allocate a buffer for relocations */
988 buf = malloc(sec->sh.sh_size);
989 if (!buf) {
990 perror("malloc");
991 return -1;
992 }
993
994 sec->data->d_buf = buf;
995 sec->data->d_size = sec->sh.sh_size;
996 sec->data->d_type = ELF_T_REL;
997
998 idx = 0;
999 list_for_each_entry(reloc, &sec->reloc_list, list) {
1000 reloc->rel.r_offset = reloc->offset;
1001 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1002 if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
1003 WARN_ELF("gelf_update_rel");
1004 return -1;
1005 }
1006 idx++;
1007 }
1008
1009 return 0;
1010 }
1011
elf_rebuild_rela_reloc_section(struct section * sec)1012 static int elf_rebuild_rela_reloc_section(struct section *sec)
1013 {
1014 struct reloc *reloc;
1015 int idx = 0;
1016 void *buf;
1017
1018 /* Allocate a buffer for relocations with addends */
1019 buf = malloc(sec->sh.sh_size);
1020 if (!buf) {
1021 perror("malloc");
1022 return -1;
1023 }
1024
1025 sec->data->d_buf = buf;
1026 sec->data->d_size = sec->sh.sh_size;
1027 sec->data->d_type = ELF_T_RELA;
1028
1029 idx = 0;
1030 list_for_each_entry(reloc, &sec->reloc_list, list) {
1031 reloc->rela.r_offset = reloc->offset;
1032 reloc->rela.r_addend = reloc->addend;
1033 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1034 if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
1035 WARN_ELF("gelf_update_rela");
1036 return -1;
1037 }
1038 idx++;
1039 }
1040
1041 return 0;
1042 }
1043
elf_rebuild_reloc_section(struct elf * elf,struct section * sec)1044 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1045 {
1046 switch (sec->sh.sh_type) {
1047 case SHT_REL: return elf_rebuild_rel_reloc_section(sec);
1048 case SHT_RELA: return elf_rebuild_rela_reloc_section(sec);
1049 default: return -1;
1050 }
1051 }
1052
elf_write_insn(struct elf * elf,struct section * sec,unsigned long offset,unsigned int len,const char * insn)1053 int elf_write_insn(struct elf *elf, struct section *sec,
1054 unsigned long offset, unsigned int len,
1055 const char *insn)
1056 {
1057 Elf_Data *data = sec->data;
1058
1059 if (data->d_type != ELF_T_BYTE || data->d_off) {
1060 WARN("write to unexpected data for section: %s", sec->name);
1061 return -1;
1062 }
1063
1064 memcpy(data->d_buf + offset, insn, len);
1065 elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1066
1067 elf->changed = true;
1068
1069 return 0;
1070 }
1071
elf_write_reloc(struct elf * elf,struct reloc * reloc)1072 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1073 {
1074 struct section *sec = reloc->sec;
1075
1076 if (sec->sh.sh_type == SHT_REL) {
1077 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1078 reloc->rel.r_offset = reloc->offset;
1079
1080 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1081 WARN_ELF("gelf_update_rel");
1082 return -1;
1083 }
1084 } else {
1085 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1086 reloc->rela.r_addend = reloc->addend;
1087 reloc->rela.r_offset = reloc->offset;
1088
1089 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1090 WARN_ELF("gelf_update_rela");
1091 return -1;
1092 }
1093 }
1094
1095 elf->changed = true;
1096
1097 return 0;
1098 }
1099
elf_write(struct elf * elf)1100 int elf_write(struct elf *elf)
1101 {
1102 struct section *sec;
1103 Elf_Scn *s;
1104
1105 /* Update changed relocation sections and section headers: */
1106 list_for_each_entry(sec, &elf->sections, list) {
1107 if (sec->changed) {
1108 s = elf_getscn(elf->elf, sec->idx);
1109 if (!s) {
1110 WARN_ELF("elf_getscn");
1111 return -1;
1112 }
1113 if (!gelf_update_shdr(s, &sec->sh)) {
1114 WARN_ELF("gelf_update_shdr");
1115 return -1;
1116 }
1117
1118 if (sec->base &&
1119 elf_rebuild_reloc_section(elf, sec)) {
1120 WARN("elf_rebuild_reloc_section");
1121 return -1;
1122 }
1123
1124 sec->changed = false;
1125 elf->changed = true;
1126 }
1127 }
1128
1129 /* Make sure the new section header entries get updated properly. */
1130 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1131
1132 /* Write all changes to the file. */
1133 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1134 WARN_ELF("elf_update");
1135 return -1;
1136 }
1137
1138 elf->changed = false;
1139
1140 return 0;
1141 }
1142
elf_close(struct elf * elf)1143 void elf_close(struct elf *elf)
1144 {
1145 struct section *sec, *tmpsec;
1146 struct symbol *sym, *tmpsym;
1147 struct reloc *reloc, *tmpreloc;
1148
1149 if (elf->elf)
1150 elf_end(elf->elf);
1151
1152 if (elf->fd > 0)
1153 close(elf->fd);
1154
1155 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1156 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1157 list_del(&sym->list);
1158 hash_del(&sym->hash);
1159 free(sym);
1160 }
1161 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1162 list_del(&reloc->list);
1163 hash_del(&reloc->hash);
1164 free(reloc);
1165 }
1166 list_del(&sec->list);
1167 free(sec);
1168 }
1169
1170 free(elf);
1171 }
1172
