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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 <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 <linux/interval_tree_generic.h>
20#include <objtool/builtin.h>
21
22#include <objtool/elf.h>
23#include <objtool/warn.h>
24
25#define MAX_NAME_LEN 128
26
27static inline u32 str_hash(const char *str)
28{
29 return jhash(str, strlen(str), 0);
30}
31
32#define __elf_table(name) (elf->name##_hash)
33#define __elf_bits(name) (elf->name##_bits)
34
35#define elf_hash_add(name, node, key) \
36 hlist_add_head(node, &__elf_table(name)[hash_min(key, __elf_bits(name))])
37
38#define elf_hash_for_each_possible(name, obj, member, key) \
39 hlist_for_each_entry(obj, &__elf_table(name)[hash_min(key, __elf_bits(name))], member)
40
41#define elf_alloc_hash(name, size) \
42({ \
43 __elf_bits(name) = max(10, ilog2(size)); \
44 __elf_table(name) = mmap(NULL, sizeof(struct hlist_head) << __elf_bits(name), \
45 PROT_READ|PROT_WRITE, \
46 MAP_PRIVATE|MAP_ANON, -1, 0); \
47 if (__elf_table(name) == (void *)-1L) { \
48 WARN("mmap fail " #name); \
49 __elf_table(name) = NULL; \
50 } \
51 __elf_table(name); \
52})
53
54static inline unsigned long __sym_start(struct symbol *s)
55{
56 return s->offset;
57}
58
59static inline unsigned long __sym_last(struct symbol *s)
60{
61 return s->offset + s->len - 1;
62}
63
64INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
65 __sym_start, __sym_last, static, __sym)
66
67#define __sym_for_each(_iter, _tree, _start, _end) \
68 for (_iter = __sym_iter_first((_tree), (_start), (_end)); \
69 _iter; _iter = __sym_iter_next(_iter, (_start), (_end)))
70
71struct symbol_hole {
72 unsigned long key;
73 const struct symbol *sym;
74};
75
76/*
77 * Find !section symbol where @offset is after it.
78 */
79static int symbol_hole_by_offset(const void *key, const struct rb_node *node)
80{
81 const struct symbol *s = rb_entry(node, struct symbol, node);
82 struct symbol_hole *sh = (void *)key;
83
84 if (sh->key < s->offset)
85 return -1;
86
87 if (sh->key >= s->offset + s->len) {
88 if (s->type != STT_SECTION)
89 sh->sym = s;
90 return 1;
91 }
92
93 return 0;
94}
95
96struct section *find_section_by_name(const struct elf *elf, const char *name)
97{
98 struct section *sec;
99
100 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
101 if (!strcmp(sec->name, name))
102 return sec;
103 }
104
105 return NULL;
106}
107
108static struct section *find_section_by_index(struct elf *elf,
109 unsigned int idx)
110{
111 struct section *sec;
112
113 elf_hash_for_each_possible(section, sec, hash, idx) {
114 if (sec->idx == idx)
115 return sec;
116 }
117
118 return NULL;
119}
120
121static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
122{
123 struct symbol *sym;
124
125 elf_hash_for_each_possible(symbol, sym, hash, idx) {
126 if (sym->idx == idx)
127 return sym;
128 }
129
130 return NULL;
131}
132
133struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
134{
135 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
136 struct symbol *iter;
137
138 __sym_for_each(iter, tree, offset, offset) {
139 if (iter->offset == offset && iter->type != STT_SECTION)
140 return iter;
141 }
142
143 return NULL;
144}
145
146struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
147{
148 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
149 struct symbol *iter;
150
151 __sym_for_each(iter, tree, offset, offset) {
152 if (iter->offset == offset && iter->type == STT_FUNC)
153 return iter;
154 }
155
156 return NULL;
157}
158
159struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
160{
161 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
162 struct symbol *iter;
163
164 __sym_for_each(iter, tree, offset, offset) {
165 if (iter->type != STT_SECTION)
166 return iter;
167 }
168
169 return NULL;
170}
171
172/*
173 * Returns size of hole starting at @offset.
174 */
175int find_symbol_hole_containing(const struct section *sec, unsigned long offset)
176{
177 struct symbol_hole hole = {
178 .key = offset,
179 .sym = NULL,
180 };
181 struct rb_node *n;
182 struct symbol *s;
183
184 /*
185 * Find the rightmost symbol for which @offset is after it.
186 */
187 n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);
188
189 /* found a symbol that contains @offset */
190 if (n)
191 return 0; /* not a hole */
192
193 /* didn't find a symbol for which @offset is after it */
194 if (!hole.sym)
195 return 0; /* not a hole */
196
197 /* @offset >= sym->offset + sym->len, find symbol after it */
198 n = rb_next(&hole.sym->node);
199 if (!n)
200 return -1; /* until end of address space */
201
202 /* hole until start of next symbol */
203 s = rb_entry(n, struct symbol, node);
204 return s->offset - offset;
205}
206
207struct symbol *find_func_containing(struct section *sec, unsigned long offset)
208{
209 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
210 struct symbol *iter;
211
212 __sym_for_each(iter, tree, offset, offset) {
213 if (iter->type == STT_FUNC)
214 return iter;
215 }
216
217 return NULL;
218}
219
220struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
221{
222 struct symbol *sym;
223
224 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
225 if (!strcmp(sym->name, name))
226 return sym;
227 }
228
229 return NULL;
230}
231
232struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
233 unsigned long offset, unsigned int len)
234{
235 struct reloc *reloc, *r = NULL;
236 unsigned long o;
237
238 if (!sec->reloc)
239 return NULL;
240
241 sec = sec->reloc;
242
243 for_offset_range(o, offset, offset + len) {
244 elf_hash_for_each_possible(reloc, reloc, hash,
245 sec_offset_hash(sec, o)) {
246 if (reloc->sec != sec)
247 continue;
248
249 if (reloc->offset >= offset && reloc->offset < offset + len) {
250 if (!r || reloc->offset < r->offset)
251 r = reloc;
252 }
253 }
254 if (r)
255 return r;
256 }
257
258 return NULL;
259}
260
261struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
262{
263 return find_reloc_by_dest_range(elf, sec, offset, 1);
264}
265
266static int read_sections(struct elf *elf)
267{
268 Elf_Scn *s = NULL;
269 struct section *sec;
270 size_t shstrndx, sections_nr;
271 int i;
272
273 if (elf_getshdrnum(elf->elf, §ions_nr)) {
274 WARN_ELF("elf_getshdrnum");
275 return -1;
276 }
277
278 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
279 WARN_ELF("elf_getshdrstrndx");
280 return -1;
281 }
282
283 if (!elf_alloc_hash(section, sections_nr) ||
284 !elf_alloc_hash(section_name, sections_nr))
285 return -1;
286
287 for (i = 0; i < sections_nr; i++) {
288 sec = malloc(sizeof(*sec));
289 if (!sec) {
290 perror("malloc");
291 return -1;
292 }
293 memset(sec, 0, sizeof(*sec));
294
295 INIT_LIST_HEAD(&sec->symbol_list);
296 INIT_LIST_HEAD(&sec->reloc_list);
297
298 s = elf_getscn(elf->elf, i);
299 if (!s) {
300 WARN_ELF("elf_getscn");
301 return -1;
302 }
303
304 sec->idx = elf_ndxscn(s);
305
306 if (!gelf_getshdr(s, &sec->sh)) {
307 WARN_ELF("gelf_getshdr");
308 return -1;
309 }
310
311 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
312 if (!sec->name) {
313 WARN_ELF("elf_strptr");
314 return -1;
315 }
316
317 if (sec->sh.sh_size != 0) {
318 sec->data = elf_getdata(s, NULL);
319 if (!sec->data) {
320 WARN_ELF("elf_getdata");
321 return -1;
322 }
323 if (sec->data->d_off != 0 ||
324 sec->data->d_size != sec->sh.sh_size) {
325 WARN("unexpected data attributes for %s",
326 sec->name);
327 return -1;
328 }
329 }
330
331 if (sec->sh.sh_flags & SHF_EXECINSTR)
332 elf->text_size += sec->sh.sh_size;
333
334 list_add_tail(&sec->list, &elf->sections);
335 elf_hash_add(section, &sec->hash, sec->idx);
336 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
337 }
338
339 if (opts.stats) {
340 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
341 printf("section_bits: %d\n", elf->section_bits);
342 }
343
344 /* sanity check, one more call to elf_nextscn() should return NULL */
345 if (elf_nextscn(elf->elf, s)) {
346 WARN("section entry mismatch");
347 return -1;
348 }
349
350 return 0;
351}
352
353static void elf_add_symbol(struct elf *elf, struct symbol *sym)
354{
355 struct list_head *entry;
356 struct rb_node *pnode;
357 struct symbol *iter;
358
359 INIT_LIST_HEAD(&sym->reloc_list);
360 INIT_LIST_HEAD(&sym->pv_target);
361 sym->alias = sym;
362
363 sym->type = GELF_ST_TYPE(sym->sym.st_info);
364 sym->bind = GELF_ST_BIND(sym->sym.st_info);
365
366 if (sym->type == STT_FILE)
367 elf->num_files++;
368
369 sym->offset = sym->sym.st_value;
370 sym->len = sym->sym.st_size;
371
372 __sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {
373 if (iter->offset == sym->offset && iter->type == sym->type)
374 iter->alias = sym;
375 }
376
377 __sym_insert(sym, &sym->sec->symbol_tree);
378 pnode = rb_prev(&sym->node);
379 if (pnode)
380 entry = &rb_entry(pnode, struct symbol, node)->list;
381 else
382 entry = &sym->sec->symbol_list;
383 list_add(&sym->list, entry);
384 elf_hash_add(symbol, &sym->hash, sym->idx);
385 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
386
387 /*
388 * Don't store empty STT_NOTYPE symbols in the rbtree. They
389 * can exist within a function, confusing the sorting.
390 */
391 if (!sym->len)
392 __sym_remove(sym, &sym->sec->symbol_tree);
393}
394
395static int read_symbols(struct elf *elf)
396{
397 struct section *symtab, *symtab_shndx, *sec;
398 struct symbol *sym, *pfunc;
399 int symbols_nr, i;
400 char *coldstr;
401 Elf_Data *shndx_data = NULL;
402 Elf32_Word shndx;
403
404 symtab = find_section_by_name(elf, ".symtab");
405 if (symtab) {
406 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
407 if (symtab_shndx)
408 shndx_data = symtab_shndx->data;
409
410 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
411 } else {
412 /*
413 * A missing symbol table is actually possible if it's an empty
414 * .o file. This can happen for thunk_64.o. Make sure to at
415 * least allocate the symbol hash tables so we can do symbol
416 * lookups without crashing.
417 */
418 symbols_nr = 0;
419 }
420
421 if (!elf_alloc_hash(symbol, symbols_nr) ||
422 !elf_alloc_hash(symbol_name, symbols_nr))
423 return -1;
424
425 for (i = 0; i < symbols_nr; i++) {
426 sym = malloc(sizeof(*sym));
427 if (!sym) {
428 perror("malloc");
429 return -1;
430 }
431 memset(sym, 0, sizeof(*sym));
432
433 sym->idx = i;
434
435 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
436 &shndx)) {
437 WARN_ELF("gelf_getsymshndx");
438 goto err;
439 }
440
441 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
442 sym->sym.st_name);
443 if (!sym->name) {
444 WARN_ELF("elf_strptr");
445 goto err;
446 }
447
448 if ((sym->sym.st_shndx > SHN_UNDEF &&
449 sym->sym.st_shndx < SHN_LORESERVE) ||
450 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
451 if (sym->sym.st_shndx != SHN_XINDEX)
452 shndx = sym->sym.st_shndx;
453
454 sym->sec = find_section_by_index(elf, shndx);
455 if (!sym->sec) {
456 WARN("couldn't find section for symbol %s",
457 sym->name);
458 goto err;
459 }
460 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
461 sym->name = sym->sec->name;
462 sym->sec->sym = sym;
463 }
464 } else
465 sym->sec = find_section_by_index(elf, 0);
466
467 elf_add_symbol(elf, sym);
468 }
469
470 if (opts.stats) {
471 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
472 printf("symbol_bits: %d\n", elf->symbol_bits);
473 }
474
475 /* Create parent/child links for any cold subfunctions */
476 list_for_each_entry(sec, &elf->sections, list) {
477 list_for_each_entry(sym, &sec->symbol_list, list) {
478 char pname[MAX_NAME_LEN + 1];
479 size_t pnamelen;
480 if (sym->type != STT_FUNC)
481 continue;
482
483 if (sym->pfunc == NULL)
484 sym->pfunc = sym;
485
486 if (sym->cfunc == NULL)
487 sym->cfunc = sym;
488
489 coldstr = strstr(sym->name, ".cold");
490 if (!coldstr)
491 continue;
492
493 pnamelen = coldstr - sym->name;
494 if (pnamelen > MAX_NAME_LEN) {
495 WARN("%s(): parent function name exceeds maximum length of %d characters",
496 sym->name, MAX_NAME_LEN);
497 return -1;
498 }
499
500 strncpy(pname, sym->name, pnamelen);
501 pname[pnamelen] = '\0';
502 pfunc = find_symbol_by_name(elf, pname);
503
504 if (!pfunc) {
505 WARN("%s(): can't find parent function",
506 sym->name);
507 return -1;
508 }
509
510 sym->pfunc = pfunc;
511 pfunc->cfunc = sym;
512
513 /*
514 * Unfortunately, -fnoreorder-functions puts the child
515 * inside the parent. Remove the overlap so we can
516 * have sane assumptions.
517 *
518 * Note that pfunc->len now no longer matches
519 * pfunc->sym.st_size.
520 */
521 if (sym->sec == pfunc->sec &&
522 sym->offset >= pfunc->offset &&
523 sym->offset + sym->len == pfunc->offset + pfunc->len) {
524 pfunc->len -= sym->len;
525 }
526 }
527 }
528
529 return 0;
530
531err:
532 free(sym);
533 return -1;
534}
535
536static struct section *elf_create_reloc_section(struct elf *elf,
537 struct section *base,
538 int reltype);
539
540int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
541 unsigned int type, struct symbol *sym, s64 addend)
542{
543 struct reloc *reloc;
544
545 if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
546 return -1;
547
548 reloc = malloc(sizeof(*reloc));
549 if (!reloc) {
550 perror("malloc");
551 return -1;
552 }
553 memset(reloc, 0, sizeof(*reloc));
554
555 reloc->sec = sec->reloc;
556 reloc->offset = offset;
557 reloc->type = type;
558 reloc->sym = sym;
559 reloc->addend = addend;
560
561 list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
562 list_add_tail(&reloc->list, &sec->reloc->reloc_list);
563 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
564
565 sec->reloc->sh.sh_size += sec->reloc->sh.sh_entsize;
566 sec->reloc->changed = true;
567
568 return 0;
569}
570
571/*
572 * Ensure that any reloc section containing references to @sym is marked
573 * changed such that it will get re-generated in elf_rebuild_reloc_sections()
574 * with the new symbol index.
575 */
576static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym)
577{
578 struct reloc *reloc;
579
580 list_for_each_entry(reloc, &sym->reloc_list, sym_reloc_entry)
581 reloc->sec->changed = true;
582}
583
584/*
585 * The libelf API is terrible; gelf_update_sym*() takes a data block relative
586 * index value, *NOT* the symbol index. As such, iterate the data blocks and
587 * adjust index until it fits.
588 *
589 * If no data block is found, allow adding a new data block provided the index
590 * is only one past the end.
591 */
592static int elf_update_symbol(struct elf *elf, struct section *symtab,
593 struct section *symtab_shndx, struct symbol *sym)
594{
595 Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
596 Elf_Data *symtab_data = NULL, *shndx_data = NULL;
597 Elf64_Xword entsize = symtab->sh.sh_entsize;
598 int max_idx, idx = sym->idx;
599 Elf_Scn *s, *t = NULL;
600 bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
601 sym->sym.st_shndx != SHN_XINDEX;
602
603 if (is_special_shndx)
604 shndx = sym->sym.st_shndx;
605
606 s = elf_getscn(elf->elf, symtab->idx);
607 if (!s) {
608 WARN_ELF("elf_getscn");
609 return -1;
610 }
611
612 if (symtab_shndx) {
613 t = elf_getscn(elf->elf, symtab_shndx->idx);
614 if (!t) {
615 WARN_ELF("elf_getscn");
616 return -1;
617 }
618 }
619
620 for (;;) {
621 /* get next data descriptor for the relevant sections */
622 symtab_data = elf_getdata(s, symtab_data);
623 if (t)
624 shndx_data = elf_getdata(t, shndx_data);
625
626 /* end-of-list */
627 if (!symtab_data) {
628 /*
629 * Over-allocate to avoid O(n^2) symbol creation
630 * behaviour. The down side is that libelf doesn't
631 * like this; see elf_truncate_section() for the fixup.
632 */
633 int num = max(1U, sym->idx/3);
634 void *buf;
635
636 if (idx) {
637 /* we don't do holes in symbol tables */
638 WARN("index out of range");
639 return -1;
640 }
641
642 /* if @idx == 0, it's the next contiguous entry, create it */
643 symtab_data = elf_newdata(s);
644 if (t)
645 shndx_data = elf_newdata(t);
646
647 buf = calloc(num, entsize);
648 if (!buf) {
649 WARN("malloc");
650 return -1;
651 }
652
653 symtab_data->d_buf = buf;
654 symtab_data->d_size = num * entsize;
655 symtab_data->d_align = 1;
656 symtab_data->d_type = ELF_T_SYM;
657
658 symtab->changed = true;
659 symtab->truncate = true;
660
661 if (t) {
662 buf = calloc(num, sizeof(Elf32_Word));
663 if (!buf) {
664 WARN("malloc");
665 return -1;
666 }
667
668 shndx_data->d_buf = buf;
669 shndx_data->d_size = num * sizeof(Elf32_Word);
670 shndx_data->d_align = sizeof(Elf32_Word);
671 shndx_data->d_type = ELF_T_WORD;
672
673 symtab_shndx->changed = true;
674 symtab_shndx->truncate = true;
675 }
676
677 break;
678 }
679
680 /* empty blocks should not happen */
681 if (!symtab_data->d_size) {
682 WARN("zero size data");
683 return -1;
684 }
685
686 /* is this the right block? */
687 max_idx = symtab_data->d_size / entsize;
688 if (idx < max_idx)
689 break;
690
691 /* adjust index and try again */
692 idx -= max_idx;
693 }
694
695 /* something went side-ways */
696 if (idx < 0) {
697 WARN("negative index");
698 return -1;
699 }
700
701 /* setup extended section index magic and write the symbol */
702 if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
703 sym->sym.st_shndx = shndx;
704 if (!shndx_data)
705 shndx = 0;
706 } else {
707 sym->sym.st_shndx = SHN_XINDEX;
708 if (!shndx_data) {
709 WARN("no .symtab_shndx");
710 return -1;
711 }
712 }
713
714 if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
715 WARN_ELF("gelf_update_symshndx");
716 return -1;
717 }
718
719 return 0;
720}
721
722static struct symbol *
723__elf_create_symbol(struct elf *elf, struct symbol *sym)
724{
725 struct section *symtab, *symtab_shndx;
726 Elf32_Word first_non_local, new_idx;
727 struct symbol *old;
728
729 symtab = find_section_by_name(elf, ".symtab");
730 if (symtab) {
731 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
732 } else {
733 WARN("no .symtab");
734 return NULL;
735 }
736
737 new_idx = symtab->sh.sh_size / symtab->sh.sh_entsize;
738
739 if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)
740 goto non_local;
741
742 /*
743 * Move the first global symbol, as per sh_info, into a new, higher
744 * symbol index. This fees up a spot for a new local symbol.
745 */
746 first_non_local = symtab->sh.sh_info;
747 old = find_symbol_by_index(elf, first_non_local);
748 if (old) {
749 old->idx = new_idx;
750
751 hlist_del(&old->hash);
752 elf_hash_add(symbol, &old->hash, old->idx);
753
754 elf_dirty_reloc_sym(elf, old);
755
756 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
757 WARN("elf_update_symbol move");
758 return NULL;
759 }
760
761 new_idx = first_non_local;
762 }
763
764 /*
765 * Either way, we will add a LOCAL symbol.
766 */
767 symtab->sh.sh_info += 1;
768
769non_local:
770 sym->idx = new_idx;
771 if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
772 WARN("elf_update_symbol");
773 return NULL;
774 }
775
776 symtab->sh.sh_size += symtab->sh.sh_entsize;
777 symtab->changed = true;
778
779 if (symtab_shndx) {
780 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
781 symtab_shndx->changed = true;
782 }
783
784 return sym;
785}
786
787static struct symbol *
788elf_create_section_symbol(struct elf *elf, struct section *sec)
789{
790 struct symbol *sym = calloc(1, sizeof(*sym));
791
792 if (!sym) {
793 perror("malloc");
794 return NULL;
795 }
796
797 sym->name = sec->name;
798 sym->sec = sec;
799
800 // st_name 0
801 sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
802 // st_other 0
803 // st_value 0
804 // st_size 0
805
806 sym = __elf_create_symbol(elf, sym);
807 if (sym)
808 elf_add_symbol(elf, sym);
809
810 return sym;
811}
812
813static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
814
815struct symbol *
816elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
817{
818 struct symbol *sym = calloc(1, sizeof(*sym));
819 size_t namelen = strlen(orig->name) + sizeof("__pfx_");
820 char *name = malloc(namelen);
821
822 if (!sym || !name) {
823 perror("malloc");
824 return NULL;
825 }
826
827 snprintf(name, namelen, "__pfx_%s", orig->name);
828
829 sym->name = name;
830 sym->sec = orig->sec;
831
832 sym->sym.st_name = elf_add_string(elf, NULL, name);
833 sym->sym.st_info = orig->sym.st_info;
834 sym->sym.st_value = orig->sym.st_value - size;
835 sym->sym.st_size = size;
836
837 sym = __elf_create_symbol(elf, sym);
838 if (sym)
839 elf_add_symbol(elf, sym);
840
841 return sym;
842}
843
844int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
845 unsigned long offset, unsigned int type,
846 struct section *insn_sec, unsigned long insn_off)
847{
848 struct symbol *sym = insn_sec->sym;
849 int addend = insn_off;
850
851 if (!sym) {
852 /*
853 * Due to how weak functions work, we must use section based
854 * relocations. Symbol based relocations would result in the
855 * weak and non-weak function annotations being overlaid on the
856 * non-weak function after linking.
857 */
858 sym = elf_create_section_symbol(elf, insn_sec);
859 if (!sym)
860 return -1;
861
862 insn_sec->sym = sym;
863 }
864
865 return elf_add_reloc(elf, sec, offset, type, sym, addend);
866}
867
868static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
869{
870 if (!gelf_getrel(sec->data, i, &reloc->rel)) {
871 WARN_ELF("gelf_getrel");
872 return -1;
873 }
874 reloc->type = GELF_R_TYPE(reloc->rel.r_info);
875 reloc->addend = 0;
876 reloc->offset = reloc->rel.r_offset;
877 *symndx = GELF_R_SYM(reloc->rel.r_info);
878 return 0;
879}
880
881static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
882{
883 if (!gelf_getrela(sec->data, i, &reloc->rela)) {
884 WARN_ELF("gelf_getrela");
885 return -1;
886 }
887 reloc->type = GELF_R_TYPE(reloc->rela.r_info);
888 reloc->addend = reloc->rela.r_addend;
889 reloc->offset = reloc->rela.r_offset;
890 *symndx = GELF_R_SYM(reloc->rela.r_info);
891 return 0;
892}
893
894static int read_relocs(struct elf *elf)
895{
896 unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
897 struct section *sec;
898 struct reloc *reloc;
899 unsigned int symndx;
900 struct symbol *sym;
901 int i;
902
903 if (!elf_alloc_hash(reloc, elf->text_size / 16))
904 return -1;
905
906 list_for_each_entry(sec, &elf->sections, list) {
907 if ((sec->sh.sh_type != SHT_RELA) &&
908 (sec->sh.sh_type != SHT_REL))
909 continue;
910
911 sec->base = find_section_by_index(elf, sec->sh.sh_info);
912 if (!sec->base) {
913 WARN("can't find base section for reloc section %s",
914 sec->name);
915 return -1;
916 }
917
918 sec->base->reloc = sec;
919
920 nr_reloc = 0;
921 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
922 reloc = malloc(sizeof(*reloc));
923 if (!reloc) {
924 perror("malloc");
925 return -1;
926 }
927 memset(reloc, 0, sizeof(*reloc));
928 switch (sec->sh.sh_type) {
929 case SHT_REL:
930 if (read_rel_reloc(sec, i, reloc, &symndx))
931 return -1;
932 break;
933 case SHT_RELA:
934 if (read_rela_reloc(sec, i, reloc, &symndx))
935 return -1;
936 break;
937 default: return -1;
938 }
939
940 reloc->sec = sec;
941 reloc->idx = i;
942 reloc->sym = sym = find_symbol_by_index(elf, symndx);
943 if (!reloc->sym) {
944 WARN("can't find reloc entry symbol %d for %s",
945 symndx, sec->name);
946 return -1;
947 }
948
949 list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
950 list_add_tail(&reloc->list, &sec->reloc_list);
951 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
952
953 nr_reloc++;
954 }
955 max_reloc = max(max_reloc, nr_reloc);
956 tot_reloc += nr_reloc;
957 }
958
959 if (opts.stats) {
960 printf("max_reloc: %lu\n", max_reloc);
961 printf("tot_reloc: %lu\n", tot_reloc);
962 printf("reloc_bits: %d\n", elf->reloc_bits);
963 }
964
965 return 0;
966}
967
968struct elf *elf_open_read(const char *name, int flags)
969{
970 struct elf *elf;
971 Elf_Cmd cmd;
972
973 elf_version(EV_CURRENT);
974
975 elf = malloc(sizeof(*elf));
976 if (!elf) {
977 perror("malloc");
978 return NULL;
979 }
980 memset(elf, 0, offsetof(struct elf, sections));
981
982 INIT_LIST_HEAD(&elf->sections);
983
984 elf->fd = open(name, flags);
985 if (elf->fd == -1) {
986 fprintf(stderr, "objtool: Can't open '%s': %s\n",
987 name, strerror(errno));
988 goto err;
989 }
990
991 if ((flags & O_ACCMODE) == O_RDONLY)
992 cmd = ELF_C_READ_MMAP;
993 else if ((flags & O_ACCMODE) == O_RDWR)
994 cmd = ELF_C_RDWR;
995 else /* O_WRONLY */
996 cmd = ELF_C_WRITE;
997
998 elf->elf = elf_begin(elf->fd, cmd, NULL);
999 if (!elf->elf) {
1000 WARN_ELF("elf_begin");
1001 goto err;
1002 }
1003
1004 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
1005 WARN_ELF("gelf_getehdr");
1006 goto err;
1007 }
1008
1009 if (read_sections(elf))
1010 goto err;
1011
1012 if (read_symbols(elf))
1013 goto err;
1014
1015 if (read_relocs(elf))
1016 goto err;
1017
1018 return elf;
1019
1020err:
1021 elf_close(elf);
1022 return NULL;
1023}
1024
1025static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
1026{
1027 Elf_Data *data;
1028 Elf_Scn *s;
1029 int len;
1030
1031 if (!strtab)
1032 strtab = find_section_by_name(elf, ".strtab");
1033 if (!strtab) {
1034 WARN("can't find .strtab section");
1035 return -1;
1036 }
1037
1038 s = elf_getscn(elf->elf, strtab->idx);
1039 if (!s) {
1040 WARN_ELF("elf_getscn");
1041 return -1;
1042 }
1043
1044 data = elf_newdata(s);
1045 if (!data) {
1046 WARN_ELF("elf_newdata");
1047 return -1;
1048 }
1049
1050 data->d_buf = str;
1051 data->d_size = strlen(str) + 1;
1052 data->d_align = 1;
1053
1054 len = strtab->sh.sh_size;
1055 strtab->sh.sh_size += data->d_size;
1056 strtab->changed = true;
1057
1058 return len;
1059}
1060
1061struct section *elf_create_section(struct elf *elf, const char *name,
1062 unsigned int sh_flags, size_t entsize, int nr)
1063{
1064 struct section *sec, *shstrtab;
1065 size_t size = entsize * nr;
1066 Elf_Scn *s;
1067
1068 sec = malloc(sizeof(*sec));
1069 if (!sec) {
1070 perror("malloc");
1071 return NULL;
1072 }
1073 memset(sec, 0, sizeof(*sec));
1074
1075 INIT_LIST_HEAD(&sec->symbol_list);
1076 INIT_LIST_HEAD(&sec->reloc_list);
1077
1078 s = elf_newscn(elf->elf);
1079 if (!s) {
1080 WARN_ELF("elf_newscn");
1081 return NULL;
1082 }
1083
1084 sec->name = strdup(name);
1085 if (!sec->name) {
1086 perror("strdup");
1087 return NULL;
1088 }
1089
1090 sec->idx = elf_ndxscn(s);
1091 sec->changed = true;
1092
1093 sec->data = elf_newdata(s);
1094 if (!sec->data) {
1095 WARN_ELF("elf_newdata");
1096 return NULL;
1097 }
1098
1099 sec->data->d_size = size;
1100 sec->data->d_align = 1;
1101
1102 if (size) {
1103 sec->data->d_buf = malloc(size);
1104 if (!sec->data->d_buf) {
1105 perror("malloc");
1106 return NULL;
1107 }
1108 memset(sec->data->d_buf, 0, size);
1109 }
1110
1111 if (!gelf_getshdr(s, &sec->sh)) {
1112 WARN_ELF("gelf_getshdr");
1113 return NULL;
1114 }
1115
1116 sec->sh.sh_size = size;
1117 sec->sh.sh_entsize = entsize;
1118 sec->sh.sh_type = SHT_PROGBITS;
1119 sec->sh.sh_addralign = 1;
1120 sec->sh.sh_flags = SHF_ALLOC | sh_flags;
1121
1122 /* Add section name to .shstrtab (or .strtab for Clang) */
1123 shstrtab = find_section_by_name(elf, ".shstrtab");
1124 if (!shstrtab)
1125 shstrtab = find_section_by_name(elf, ".strtab");
1126 if (!shstrtab) {
1127 WARN("can't find .shstrtab or .strtab section");
1128 return NULL;
1129 }
1130 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
1131 if (sec->sh.sh_name == -1)
1132 return NULL;
1133
1134 list_add_tail(&sec->list, &elf->sections);
1135 elf_hash_add(section, &sec->hash, sec->idx);
1136 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
1137
1138 elf->changed = true;
1139
1140 return sec;
1141}
1142
1143static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
1144{
1145 char *relocname;
1146 struct section *sec;
1147
1148 relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
1149 if (!relocname) {
1150 perror("malloc");
1151 return NULL;
1152 }
1153 strcpy(relocname, ".rel");
1154 strcat(relocname, base->name);
1155
1156 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
1157 free(relocname);
1158 if (!sec)
1159 return NULL;
1160
1161 base->reloc = sec;
1162 sec->base = base;
1163
1164 sec->sh.sh_type = SHT_REL;
1165 sec->sh.sh_addralign = 8;
1166 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1167 sec->sh.sh_info = base->idx;
1168 sec->sh.sh_flags = SHF_INFO_LINK;
1169
1170 return sec;
1171}
1172
1173static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
1174{
1175 char *relocname;
1176 struct section *sec;
1177 int addrsize = elf_class_addrsize(elf);
1178
1179 relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
1180 if (!relocname) {
1181 perror("malloc");
1182 return NULL;
1183 }
1184 strcpy(relocname, ".rela");
1185 strcat(relocname, base->name);
1186
1187 if (addrsize == sizeof(u32))
1188 sec = elf_create_section(elf, relocname, 0, sizeof(Elf32_Rela), 0);
1189 else
1190 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
1191 free(relocname);
1192 if (!sec)
1193 return NULL;
1194
1195 base->reloc = sec;
1196 sec->base = base;
1197
1198 sec->sh.sh_type = SHT_RELA;
1199 sec->sh.sh_addralign = addrsize;
1200 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1201 sec->sh.sh_info = base->idx;
1202 sec->sh.sh_flags = SHF_INFO_LINK;
1203
1204 return sec;
1205}
1206
1207static struct section *elf_create_reloc_section(struct elf *elf,
1208 struct section *base,
1209 int reltype)
1210{
1211 switch (reltype) {
1212 case SHT_REL: return elf_create_rel_reloc_section(elf, base);
1213 case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
1214 default: return NULL;
1215 }
1216}
1217
1218static int elf_rebuild_rel_reloc_section(struct section *sec)
1219{
1220 struct reloc *reloc;
1221 int idx = 0;
1222 void *buf;
1223
1224 /* Allocate a buffer for relocations */
1225 buf = malloc(sec->sh.sh_size);
1226 if (!buf) {
1227 perror("malloc");
1228 return -1;
1229 }
1230
1231 sec->data->d_buf = buf;
1232 sec->data->d_size = sec->sh.sh_size;
1233 sec->data->d_type = ELF_T_REL;
1234
1235 idx = 0;
1236 list_for_each_entry(reloc, &sec->reloc_list, list) {
1237 reloc->rel.r_offset = reloc->offset;
1238 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1239 if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
1240 WARN_ELF("gelf_update_rel");
1241 return -1;
1242 }
1243 idx++;
1244 }
1245
1246 return 0;
1247}
1248
1249static int elf_rebuild_rela_reloc_section(struct section *sec)
1250{
1251 struct reloc *reloc;
1252 int idx = 0;
1253 void *buf;
1254
1255 /* Allocate a buffer for relocations with addends */
1256 buf = malloc(sec->sh.sh_size);
1257 if (!buf) {
1258 perror("malloc");
1259 return -1;
1260 }
1261
1262 sec->data->d_buf = buf;
1263 sec->data->d_size = sec->sh.sh_size;
1264 sec->data->d_type = ELF_T_RELA;
1265
1266 idx = 0;
1267 list_for_each_entry(reloc, &sec->reloc_list, list) {
1268 reloc->rela.r_offset = reloc->offset;
1269 reloc->rela.r_addend = reloc->addend;
1270 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1271 if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
1272 WARN_ELF("gelf_update_rela");
1273 return -1;
1274 }
1275 idx++;
1276 }
1277
1278 return 0;
1279}
1280
1281static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1282{
1283 switch (sec->sh.sh_type) {
1284 case SHT_REL: return elf_rebuild_rel_reloc_section(sec);
1285 case SHT_RELA: return elf_rebuild_rela_reloc_section(sec);
1286 default: return -1;
1287 }
1288}
1289
1290int elf_write_insn(struct elf *elf, struct section *sec,
1291 unsigned long offset, unsigned int len,
1292 const char *insn)
1293{
1294 Elf_Data *data = sec->data;
1295
1296 if (data->d_type != ELF_T_BYTE || data->d_off) {
1297 WARN("write to unexpected data for section: %s", sec->name);
1298 return -1;
1299 }
1300
1301 memcpy(data->d_buf + offset, insn, len);
1302 elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1303
1304 elf->changed = true;
1305
1306 return 0;
1307}
1308
1309int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1310{
1311 struct section *sec = reloc->sec;
1312
1313 if (sec->sh.sh_type == SHT_REL) {
1314 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1315 reloc->rel.r_offset = reloc->offset;
1316
1317 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1318 WARN_ELF("gelf_update_rel");
1319 return -1;
1320 }
1321 } else {
1322 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1323 reloc->rela.r_addend = reloc->addend;
1324 reloc->rela.r_offset = reloc->offset;
1325
1326 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1327 WARN_ELF("gelf_update_rela");
1328 return -1;
1329 }
1330 }
1331
1332 elf->changed = true;
1333
1334 return 0;
1335}
1336
1337/*
1338 * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size
1339 * do you:
1340 *
1341 * A) adhere to the section header and truncate the data, or
1342 * B) ignore the section header and write out all the data you've got?
1343 *
1344 * Yes, libelf sucks and we need to manually truncate if we over-allocate data.
1345 */
1346static int elf_truncate_section(struct elf *elf, struct section *sec)
1347{
1348 u64 size = sec->sh.sh_size;
1349 bool truncated = false;
1350 Elf_Data *data = NULL;
1351 Elf_Scn *s;
1352
1353 s = elf_getscn(elf->elf, sec->idx);
1354 if (!s) {
1355 WARN_ELF("elf_getscn");
1356 return -1;
1357 }
1358
1359 for (;;) {
1360 /* get next data descriptor for the relevant section */
1361 data = elf_getdata(s, data);
1362
1363 if (!data) {
1364 if (size) {
1365 WARN("end of section data but non-zero size left\n");
1366 return -1;
1367 }
1368 return 0;
1369 }
1370
1371 if (truncated) {
1372 /* when we remove symbols */
1373 WARN("truncated; but more data\n");
1374 return -1;
1375 }
1376
1377 if (!data->d_size) {
1378 WARN("zero size data");
1379 return -1;
1380 }
1381
1382 if (data->d_size > size) {
1383 truncated = true;
1384 data->d_size = size;
1385 }
1386
1387 size -= data->d_size;
1388 }
1389}
1390
1391int elf_write(struct elf *elf)
1392{
1393 struct section *sec;
1394 Elf_Scn *s;
1395
1396 if (opts.dryrun)
1397 return 0;
1398
1399 /* Update changed relocation sections and section headers: */
1400 list_for_each_entry(sec, &elf->sections, list) {
1401 if (sec->truncate)
1402 elf_truncate_section(elf, sec);
1403
1404 if (sec->changed) {
1405 s = elf_getscn(elf->elf, sec->idx);
1406 if (!s) {
1407 WARN_ELF("elf_getscn");
1408 return -1;
1409 }
1410 if (!gelf_update_shdr(s, &sec->sh)) {
1411 WARN_ELF("gelf_update_shdr");
1412 return -1;
1413 }
1414
1415 if (sec->base &&
1416 elf_rebuild_reloc_section(elf, sec)) {
1417 WARN("elf_rebuild_reloc_section");
1418 return -1;
1419 }
1420
1421 sec->changed = false;
1422 elf->changed = true;
1423 }
1424 }
1425
1426 /* Make sure the new section header entries get updated properly. */
1427 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1428
1429 /* Write all changes to the file. */
1430 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1431 WARN_ELF("elf_update");
1432 return -1;
1433 }
1434
1435 elf->changed = false;
1436
1437 return 0;
1438}
1439
1440void elf_close(struct elf *elf)
1441{
1442 struct section *sec, *tmpsec;
1443 struct symbol *sym, *tmpsym;
1444 struct reloc *reloc, *tmpreloc;
1445
1446 if (elf->elf)
1447 elf_end(elf->elf);
1448
1449 if (elf->fd > 0)
1450 close(elf->fd);
1451
1452 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1453 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1454 list_del(&sym->list);
1455 hash_del(&sym->hash);
1456 free(sym);
1457 }
1458 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1459 list_del(&reloc->list);
1460 hash_del(&reloc->hash);
1461 free(reloc);
1462 }
1463 list_del(&sec->list);
1464 free(sec);
1465 }
1466
1467 free(elf);
1468}
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 <linux/interval_tree_generic.h>
20#include <objtool/builtin.h>
21
22#include <objtool/elf.h>
23#include <objtool/warn.h>
24
25static inline u32 str_hash(const char *str)
26{
27 return jhash(str, strlen(str), 0);
28}
29
30#define __elf_table(name) (elf->name##_hash)
31#define __elf_bits(name) (elf->name##_bits)
32
33#define __elf_table_entry(name, key) \
34 __elf_table(name)[hash_min(key, __elf_bits(name))]
35
36#define elf_hash_add(name, node, key) \
37({ \
38 struct elf_hash_node *__node = node; \
39 __node->next = __elf_table_entry(name, key); \
40 __elf_table_entry(name, key) = __node; \
41})
42
43static inline void __elf_hash_del(struct elf_hash_node *node,
44 struct elf_hash_node **head)
45{
46 struct elf_hash_node *cur, *prev;
47
48 if (node == *head) {
49 *head = node->next;
50 return;
51 }
52
53 for (prev = NULL, cur = *head; cur; prev = cur, cur = cur->next) {
54 if (cur == node) {
55 prev->next = cur->next;
56 break;
57 }
58 }
59}
60
61#define elf_hash_del(name, node, key) \
62 __elf_hash_del(node, &__elf_table_entry(name, key))
63
64#define elf_list_entry(ptr, type, member) \
65({ \
66 typeof(ptr) __ptr = (ptr); \
67 __ptr ? container_of(__ptr, type, member) : NULL; \
68})
69
70#define elf_hash_for_each_possible(name, obj, member, key) \
71 for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \
72 obj; \
73 obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))
74
75#define elf_alloc_hash(name, size) \
76({ \
77 __elf_bits(name) = max(10, ilog2(size)); \
78 __elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \
79 PROT_READ|PROT_WRITE, \
80 MAP_PRIVATE|MAP_ANON, -1, 0); \
81 if (__elf_table(name) == (void *)-1L) { \
82 WARN("mmap fail " #name); \
83 __elf_table(name) = NULL; \
84 } \
85 __elf_table(name); \
86})
87
88static inline unsigned long __sym_start(struct symbol *s)
89{
90 return s->offset;
91}
92
93static inline unsigned long __sym_last(struct symbol *s)
94{
95 return s->offset + s->len - 1;
96}
97
98INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
99 __sym_start, __sym_last, static, __sym)
100
101#define __sym_for_each(_iter, _tree, _start, _end) \
102 for (_iter = __sym_iter_first((_tree), (_start), (_end)); \
103 _iter; _iter = __sym_iter_next(_iter, (_start), (_end)))
104
105struct symbol_hole {
106 unsigned long key;
107 const struct symbol *sym;
108};
109
110/*
111 * Find !section symbol where @offset is after it.
112 */
113static int symbol_hole_by_offset(const void *key, const struct rb_node *node)
114{
115 const struct symbol *s = rb_entry(node, struct symbol, node);
116 struct symbol_hole *sh = (void *)key;
117
118 if (sh->key < s->offset)
119 return -1;
120
121 if (sh->key >= s->offset + s->len) {
122 if (s->type != STT_SECTION)
123 sh->sym = s;
124 return 1;
125 }
126
127 return 0;
128}
129
130struct section *find_section_by_name(const struct elf *elf, const char *name)
131{
132 struct section *sec;
133
134 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
135 if (!strcmp(sec->name, name))
136 return sec;
137 }
138
139 return NULL;
140}
141
142static struct section *find_section_by_index(struct elf *elf,
143 unsigned int idx)
144{
145 struct section *sec;
146
147 elf_hash_for_each_possible(section, sec, hash, idx) {
148 if (sec->idx == idx)
149 return sec;
150 }
151
152 return NULL;
153}
154
155static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
156{
157 struct symbol *sym;
158
159 elf_hash_for_each_possible(symbol, sym, hash, idx) {
160 if (sym->idx == idx)
161 return sym;
162 }
163
164 return NULL;
165}
166
167struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
168{
169 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
170 struct symbol *iter;
171
172 __sym_for_each(iter, tree, offset, offset) {
173 if (iter->offset == offset && iter->type != STT_SECTION)
174 return iter;
175 }
176
177 return NULL;
178}
179
180struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
181{
182 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
183 struct symbol *iter;
184
185 __sym_for_each(iter, tree, offset, offset) {
186 if (iter->offset == offset && iter->type == STT_FUNC)
187 return iter;
188 }
189
190 return NULL;
191}
192
193struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
194{
195 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
196 struct symbol *iter;
197
198 __sym_for_each(iter, tree, offset, offset) {
199 if (iter->type != STT_SECTION)
200 return iter;
201 }
202
203 return NULL;
204}
205
206/*
207 * Returns size of hole starting at @offset.
208 */
209int find_symbol_hole_containing(const struct section *sec, unsigned long offset)
210{
211 struct symbol_hole hole = {
212 .key = offset,
213 .sym = NULL,
214 };
215 struct rb_node *n;
216 struct symbol *s;
217
218 /*
219 * Find the rightmost symbol for which @offset is after it.
220 */
221 n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);
222
223 /* found a symbol that contains @offset */
224 if (n)
225 return 0; /* not a hole */
226
227 /*
228 * @offset >= sym->offset + sym->len, find symbol after it.
229 * When hole.sym is empty, use the first node to compute the hole.
230 * If there is no symbol in the section, the first node will be NULL,
231 * in which case, -1 is returned to skip the whole section.
232 */
233 if (hole.sym)
234 n = rb_next(&hole.sym->node);
235 else
236 n = rb_first_cached(&sec->symbol_tree);
237
238 if (!n)
239 return -1; /* until end of address space */
240
241 /* hole until start of next symbol */
242 s = rb_entry(n, struct symbol, node);
243 return s->offset - offset;
244}
245
246struct symbol *find_func_containing(struct section *sec, unsigned long offset)
247{
248 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
249 struct symbol *iter;
250
251 __sym_for_each(iter, tree, offset, offset) {
252 if (iter->type == STT_FUNC)
253 return iter;
254 }
255
256 return NULL;
257}
258
259struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
260{
261 struct symbol *sym;
262
263 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
264 if (!strcmp(sym->name, name))
265 return sym;
266 }
267
268 return NULL;
269}
270
271struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
272 unsigned long offset, unsigned int len)
273{
274 struct reloc *reloc, *r = NULL;
275 struct section *rsec;
276 unsigned long o;
277
278 rsec = sec->rsec;
279 if (!rsec)
280 return NULL;
281
282 for_offset_range(o, offset, offset + len) {
283 elf_hash_for_each_possible(reloc, reloc, hash,
284 sec_offset_hash(rsec, o)) {
285 if (reloc->sec != rsec)
286 continue;
287
288 if (reloc_offset(reloc) >= offset &&
289 reloc_offset(reloc) < offset + len) {
290 if (!r || reloc_offset(reloc) < reloc_offset(r))
291 r = reloc;
292 }
293 }
294 if (r)
295 return r;
296 }
297
298 return NULL;
299}
300
301struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
302{
303 return find_reloc_by_dest_range(elf, sec, offset, 1);
304}
305
306static bool is_dwarf_section(struct section *sec)
307{
308 return !strncmp(sec->name, ".debug_", 7);
309}
310
311static int read_sections(struct elf *elf)
312{
313 Elf_Scn *s = NULL;
314 struct section *sec;
315 size_t shstrndx, sections_nr;
316 int i;
317
318 if (elf_getshdrnum(elf->elf, §ions_nr)) {
319 WARN_ELF("elf_getshdrnum");
320 return -1;
321 }
322
323 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
324 WARN_ELF("elf_getshdrstrndx");
325 return -1;
326 }
327
328 if (!elf_alloc_hash(section, sections_nr) ||
329 !elf_alloc_hash(section_name, sections_nr))
330 return -1;
331
332 elf->section_data = calloc(sections_nr, sizeof(*sec));
333 if (!elf->section_data) {
334 perror("calloc");
335 return -1;
336 }
337 for (i = 0; i < sections_nr; i++) {
338 sec = &elf->section_data[i];
339
340 INIT_LIST_HEAD(&sec->symbol_list);
341
342 s = elf_getscn(elf->elf, i);
343 if (!s) {
344 WARN_ELF("elf_getscn");
345 return -1;
346 }
347
348 sec->idx = elf_ndxscn(s);
349
350 if (!gelf_getshdr(s, &sec->sh)) {
351 WARN_ELF("gelf_getshdr");
352 return -1;
353 }
354
355 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
356 if (!sec->name) {
357 WARN_ELF("elf_strptr");
358 return -1;
359 }
360
361 if (sec->sh.sh_size != 0 && !is_dwarf_section(sec)) {
362 sec->data = elf_getdata(s, NULL);
363 if (!sec->data) {
364 WARN_ELF("elf_getdata");
365 return -1;
366 }
367 if (sec->data->d_off != 0 ||
368 sec->data->d_size != sec->sh.sh_size) {
369 WARN("unexpected data attributes for %s",
370 sec->name);
371 return -1;
372 }
373 }
374
375 list_add_tail(&sec->list, &elf->sections);
376 elf_hash_add(section, &sec->hash, sec->idx);
377 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
378
379 if (is_reloc_sec(sec))
380 elf->num_relocs += sec_num_entries(sec);
381 }
382
383 if (opts.stats) {
384 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
385 printf("section_bits: %d\n", elf->section_bits);
386 }
387
388 /* sanity check, one more call to elf_nextscn() should return NULL */
389 if (elf_nextscn(elf->elf, s)) {
390 WARN("section entry mismatch");
391 return -1;
392 }
393
394 return 0;
395}
396
397static void elf_add_symbol(struct elf *elf, struct symbol *sym)
398{
399 struct list_head *entry;
400 struct rb_node *pnode;
401 struct symbol *iter;
402
403 INIT_LIST_HEAD(&sym->pv_target);
404 sym->alias = sym;
405
406 sym->type = GELF_ST_TYPE(sym->sym.st_info);
407 sym->bind = GELF_ST_BIND(sym->sym.st_info);
408
409 if (sym->type == STT_FILE)
410 elf->num_files++;
411
412 sym->offset = sym->sym.st_value;
413 sym->len = sym->sym.st_size;
414
415 __sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {
416 if (iter->offset == sym->offset && iter->type == sym->type)
417 iter->alias = sym;
418 }
419
420 __sym_insert(sym, &sym->sec->symbol_tree);
421 pnode = rb_prev(&sym->node);
422 if (pnode)
423 entry = &rb_entry(pnode, struct symbol, node)->list;
424 else
425 entry = &sym->sec->symbol_list;
426 list_add(&sym->list, entry);
427 elf_hash_add(symbol, &sym->hash, sym->idx);
428 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
429
430 /*
431 * Don't store empty STT_NOTYPE symbols in the rbtree. They
432 * can exist within a function, confusing the sorting.
433 */
434 if (!sym->len)
435 __sym_remove(sym, &sym->sec->symbol_tree);
436}
437
438static int read_symbols(struct elf *elf)
439{
440 struct section *symtab, *symtab_shndx, *sec;
441 struct symbol *sym, *pfunc;
442 int symbols_nr, i;
443 char *coldstr;
444 Elf_Data *shndx_data = NULL;
445 Elf32_Word shndx;
446
447 symtab = find_section_by_name(elf, ".symtab");
448 if (symtab) {
449 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
450 if (symtab_shndx)
451 shndx_data = symtab_shndx->data;
452
453 symbols_nr = sec_num_entries(symtab);
454 } else {
455 /*
456 * A missing symbol table is actually possible if it's an empty
457 * .o file. This can happen for thunk_64.o. Make sure to at
458 * least allocate the symbol hash tables so we can do symbol
459 * lookups without crashing.
460 */
461 symbols_nr = 0;
462 }
463
464 if (!elf_alloc_hash(symbol, symbols_nr) ||
465 !elf_alloc_hash(symbol_name, symbols_nr))
466 return -1;
467
468 elf->symbol_data = calloc(symbols_nr, sizeof(*sym));
469 if (!elf->symbol_data) {
470 perror("calloc");
471 return -1;
472 }
473 for (i = 0; i < symbols_nr; i++) {
474 sym = &elf->symbol_data[i];
475
476 sym->idx = i;
477
478 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
479 &shndx)) {
480 WARN_ELF("gelf_getsymshndx");
481 goto err;
482 }
483
484 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
485 sym->sym.st_name);
486 if (!sym->name) {
487 WARN_ELF("elf_strptr");
488 goto err;
489 }
490
491 if ((sym->sym.st_shndx > SHN_UNDEF &&
492 sym->sym.st_shndx < SHN_LORESERVE) ||
493 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
494 if (sym->sym.st_shndx != SHN_XINDEX)
495 shndx = sym->sym.st_shndx;
496
497 sym->sec = find_section_by_index(elf, shndx);
498 if (!sym->sec) {
499 WARN("couldn't find section for symbol %s",
500 sym->name);
501 goto err;
502 }
503 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
504 sym->name = sym->sec->name;
505 sym->sec->sym = sym;
506 }
507 } else
508 sym->sec = find_section_by_index(elf, 0);
509
510 elf_add_symbol(elf, sym);
511 }
512
513 if (opts.stats) {
514 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
515 printf("symbol_bits: %d\n", elf->symbol_bits);
516 }
517
518 /* Create parent/child links for any cold subfunctions */
519 list_for_each_entry(sec, &elf->sections, list) {
520 sec_for_each_sym(sec, sym) {
521 char *pname;
522 size_t pnamelen;
523 if (sym->type != STT_FUNC)
524 continue;
525
526 if (sym->pfunc == NULL)
527 sym->pfunc = sym;
528
529 if (sym->cfunc == NULL)
530 sym->cfunc = sym;
531
532 coldstr = strstr(sym->name, ".cold");
533 if (!coldstr)
534 continue;
535
536 pnamelen = coldstr - sym->name;
537 pname = strndup(sym->name, pnamelen);
538 if (!pname) {
539 WARN("%s(): failed to allocate memory",
540 sym->name);
541 return -1;
542 }
543
544 pfunc = find_symbol_by_name(elf, pname);
545 free(pname);
546
547 if (!pfunc) {
548 WARN("%s(): can't find parent function",
549 sym->name);
550 return -1;
551 }
552
553 sym->pfunc = pfunc;
554 pfunc->cfunc = sym;
555
556 /*
557 * Unfortunately, -fnoreorder-functions puts the child
558 * inside the parent. Remove the overlap so we can
559 * have sane assumptions.
560 *
561 * Note that pfunc->len now no longer matches
562 * pfunc->sym.st_size.
563 */
564 if (sym->sec == pfunc->sec &&
565 sym->offset >= pfunc->offset &&
566 sym->offset + sym->len == pfunc->offset + pfunc->len) {
567 pfunc->len -= sym->len;
568 }
569 }
570 }
571
572 return 0;
573
574err:
575 free(sym);
576 return -1;
577}
578
579/*
580 * @sym's idx has changed. Update the relocs which reference it.
581 */
582static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym)
583{
584 struct reloc *reloc;
585
586 for (reloc = sym->relocs; reloc; reloc = reloc->sym_next_reloc)
587 set_reloc_sym(elf, reloc, reloc->sym->idx);
588
589 return 0;
590}
591
592/*
593 * The libelf API is terrible; gelf_update_sym*() takes a data block relative
594 * index value, *NOT* the symbol index. As such, iterate the data blocks and
595 * adjust index until it fits.
596 *
597 * If no data block is found, allow adding a new data block provided the index
598 * is only one past the end.
599 */
600static int elf_update_symbol(struct elf *elf, struct section *symtab,
601 struct section *symtab_shndx, struct symbol *sym)
602{
603 Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
604 Elf_Data *symtab_data = NULL, *shndx_data = NULL;
605 Elf64_Xword entsize = symtab->sh.sh_entsize;
606 int max_idx, idx = sym->idx;
607 Elf_Scn *s, *t = NULL;
608 bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
609 sym->sym.st_shndx != SHN_XINDEX;
610
611 if (is_special_shndx)
612 shndx = sym->sym.st_shndx;
613
614 s = elf_getscn(elf->elf, symtab->idx);
615 if (!s) {
616 WARN_ELF("elf_getscn");
617 return -1;
618 }
619
620 if (symtab_shndx) {
621 t = elf_getscn(elf->elf, symtab_shndx->idx);
622 if (!t) {
623 WARN_ELF("elf_getscn");
624 return -1;
625 }
626 }
627
628 for (;;) {
629 /* get next data descriptor for the relevant sections */
630 symtab_data = elf_getdata(s, symtab_data);
631 if (t)
632 shndx_data = elf_getdata(t, shndx_data);
633
634 /* end-of-list */
635 if (!symtab_data) {
636 /*
637 * Over-allocate to avoid O(n^2) symbol creation
638 * behaviour. The down side is that libelf doesn't
639 * like this; see elf_truncate_section() for the fixup.
640 */
641 int num = max(1U, sym->idx/3);
642 void *buf;
643
644 if (idx) {
645 /* we don't do holes in symbol tables */
646 WARN("index out of range");
647 return -1;
648 }
649
650 /* if @idx == 0, it's the next contiguous entry, create it */
651 symtab_data = elf_newdata(s);
652 if (t)
653 shndx_data = elf_newdata(t);
654
655 buf = calloc(num, entsize);
656 if (!buf) {
657 WARN("malloc");
658 return -1;
659 }
660
661 symtab_data->d_buf = buf;
662 symtab_data->d_size = num * entsize;
663 symtab_data->d_align = 1;
664 symtab_data->d_type = ELF_T_SYM;
665
666 mark_sec_changed(elf, symtab, true);
667 symtab->truncate = true;
668
669 if (t) {
670 buf = calloc(num, sizeof(Elf32_Word));
671 if (!buf) {
672 WARN("malloc");
673 return -1;
674 }
675
676 shndx_data->d_buf = buf;
677 shndx_data->d_size = num * sizeof(Elf32_Word);
678 shndx_data->d_align = sizeof(Elf32_Word);
679 shndx_data->d_type = ELF_T_WORD;
680
681 mark_sec_changed(elf, symtab_shndx, true);
682 symtab_shndx->truncate = true;
683 }
684
685 break;
686 }
687
688 /* empty blocks should not happen */
689 if (!symtab_data->d_size) {
690 WARN("zero size data");
691 return -1;
692 }
693
694 /* is this the right block? */
695 max_idx = symtab_data->d_size / entsize;
696 if (idx < max_idx)
697 break;
698
699 /* adjust index and try again */
700 idx -= max_idx;
701 }
702
703 /* something went side-ways */
704 if (idx < 0) {
705 WARN("negative index");
706 return -1;
707 }
708
709 /* setup extended section index magic and write the symbol */
710 if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
711 sym->sym.st_shndx = shndx;
712 if (!shndx_data)
713 shndx = 0;
714 } else {
715 sym->sym.st_shndx = SHN_XINDEX;
716 if (!shndx_data) {
717 WARN("no .symtab_shndx");
718 return -1;
719 }
720 }
721
722 if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
723 WARN_ELF("gelf_update_symshndx");
724 return -1;
725 }
726
727 return 0;
728}
729
730static struct symbol *
731__elf_create_symbol(struct elf *elf, struct symbol *sym)
732{
733 struct section *symtab, *symtab_shndx;
734 Elf32_Word first_non_local, new_idx;
735 struct symbol *old;
736
737 symtab = find_section_by_name(elf, ".symtab");
738 if (symtab) {
739 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
740 } else {
741 WARN("no .symtab");
742 return NULL;
743 }
744
745 new_idx = sec_num_entries(symtab);
746
747 if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)
748 goto non_local;
749
750 /*
751 * Move the first global symbol, as per sh_info, into a new, higher
752 * symbol index. This fees up a spot for a new local symbol.
753 */
754 first_non_local = symtab->sh.sh_info;
755 old = find_symbol_by_index(elf, first_non_local);
756 if (old) {
757
758 elf_hash_del(symbol, &old->hash, old->idx);
759 elf_hash_add(symbol, &old->hash, new_idx);
760 old->idx = new_idx;
761
762 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
763 WARN("elf_update_symbol move");
764 return NULL;
765 }
766
767 if (elf_update_sym_relocs(elf, old))
768 return NULL;
769
770 new_idx = first_non_local;
771 }
772
773 /*
774 * Either way, we will add a LOCAL symbol.
775 */
776 symtab->sh.sh_info += 1;
777
778non_local:
779 sym->idx = new_idx;
780 if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
781 WARN("elf_update_symbol");
782 return NULL;
783 }
784
785 symtab->sh.sh_size += symtab->sh.sh_entsize;
786 mark_sec_changed(elf, symtab, true);
787
788 if (symtab_shndx) {
789 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
790 mark_sec_changed(elf, symtab_shndx, true);
791 }
792
793 return sym;
794}
795
796static struct symbol *
797elf_create_section_symbol(struct elf *elf, struct section *sec)
798{
799 struct symbol *sym = calloc(1, sizeof(*sym));
800
801 if (!sym) {
802 perror("malloc");
803 return NULL;
804 }
805
806 sym->name = sec->name;
807 sym->sec = sec;
808
809 // st_name 0
810 sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
811 // st_other 0
812 // st_value 0
813 // st_size 0
814
815 sym = __elf_create_symbol(elf, sym);
816 if (sym)
817 elf_add_symbol(elf, sym);
818
819 return sym;
820}
821
822static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
823
824struct symbol *
825elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
826{
827 struct symbol *sym = calloc(1, sizeof(*sym));
828 size_t namelen = strlen(orig->name) + sizeof("__pfx_");
829 char *name = malloc(namelen);
830
831 if (!sym || !name) {
832 perror("malloc");
833 return NULL;
834 }
835
836 snprintf(name, namelen, "__pfx_%s", orig->name);
837
838 sym->name = name;
839 sym->sec = orig->sec;
840
841 sym->sym.st_name = elf_add_string(elf, NULL, name);
842 sym->sym.st_info = orig->sym.st_info;
843 sym->sym.st_value = orig->sym.st_value - size;
844 sym->sym.st_size = size;
845
846 sym = __elf_create_symbol(elf, sym);
847 if (sym)
848 elf_add_symbol(elf, sym);
849
850 return sym;
851}
852
853static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
854 unsigned int reloc_idx,
855 unsigned long offset, struct symbol *sym,
856 s64 addend, unsigned int type)
857{
858 struct reloc *reloc, empty = { 0 };
859
860 if (reloc_idx >= sec_num_entries(rsec)) {
861 WARN("%s: bad reloc_idx %u for %s with %d relocs",
862 __func__, reloc_idx, rsec->name, sec_num_entries(rsec));
863 return NULL;
864 }
865
866 reloc = &rsec->relocs[reloc_idx];
867
868 if (memcmp(reloc, &empty, sizeof(empty))) {
869 WARN("%s: %s: reloc %d already initialized!",
870 __func__, rsec->name, reloc_idx);
871 return NULL;
872 }
873
874 reloc->sec = rsec;
875 reloc->sym = sym;
876
877 set_reloc_offset(elf, reloc, offset);
878 set_reloc_sym(elf, reloc, sym->idx);
879 set_reloc_type(elf, reloc, type);
880 set_reloc_addend(elf, reloc, addend);
881
882 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
883 reloc->sym_next_reloc = sym->relocs;
884 sym->relocs = reloc;
885
886 return reloc;
887}
888
889struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec,
890 unsigned long offset,
891 unsigned int reloc_idx,
892 struct section *insn_sec,
893 unsigned long insn_off)
894{
895 struct symbol *sym = insn_sec->sym;
896 int addend = insn_off;
897
898 if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) {
899 WARN("bad call to %s() for data symbol %s",
900 __func__, sym->name);
901 return NULL;
902 }
903
904 if (!sym) {
905 /*
906 * Due to how weak functions work, we must use section based
907 * relocations. Symbol based relocations would result in the
908 * weak and non-weak function annotations being overlaid on the
909 * non-weak function after linking.
910 */
911 sym = elf_create_section_symbol(elf, insn_sec);
912 if (!sym)
913 return NULL;
914
915 insn_sec->sym = sym;
916 }
917
918 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
919 elf_text_rela_type(elf));
920}
921
922struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
923 unsigned long offset,
924 unsigned int reloc_idx,
925 struct symbol *sym,
926 s64 addend)
927{
928 if (sym->sec && (sec->sh.sh_flags & SHF_EXECINSTR)) {
929 WARN("bad call to %s() for text symbol %s",
930 __func__, sym->name);
931 return NULL;
932 }
933
934 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
935 elf_data_rela_type(elf));
936}
937
938static int read_relocs(struct elf *elf)
939{
940 unsigned long nr_reloc, max_reloc = 0;
941 struct section *rsec;
942 struct reloc *reloc;
943 unsigned int symndx;
944 struct symbol *sym;
945 int i;
946
947 if (!elf_alloc_hash(reloc, elf->num_relocs))
948 return -1;
949
950 list_for_each_entry(rsec, &elf->sections, list) {
951 if (!is_reloc_sec(rsec))
952 continue;
953
954 rsec->base = find_section_by_index(elf, rsec->sh.sh_info);
955 if (!rsec->base) {
956 WARN("can't find base section for reloc section %s",
957 rsec->name);
958 return -1;
959 }
960
961 rsec->base->rsec = rsec;
962
963 nr_reloc = 0;
964 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));
965 if (!rsec->relocs) {
966 perror("calloc");
967 return -1;
968 }
969 for (i = 0; i < sec_num_entries(rsec); i++) {
970 reloc = &rsec->relocs[i];
971
972 reloc->sec = rsec;
973 symndx = reloc_sym(reloc);
974 reloc->sym = sym = find_symbol_by_index(elf, symndx);
975 if (!reloc->sym) {
976 WARN("can't find reloc entry symbol %d for %s",
977 symndx, rsec->name);
978 return -1;
979 }
980
981 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
982 reloc->sym_next_reloc = sym->relocs;
983 sym->relocs = reloc;
984
985 nr_reloc++;
986 }
987 max_reloc = max(max_reloc, nr_reloc);
988 }
989
990 if (opts.stats) {
991 printf("max_reloc: %lu\n", max_reloc);
992 printf("num_relocs: %lu\n", elf->num_relocs);
993 printf("reloc_bits: %d\n", elf->reloc_bits);
994 }
995
996 return 0;
997}
998
999struct elf *elf_open_read(const char *name, int flags)
1000{
1001 struct elf *elf;
1002 Elf_Cmd cmd;
1003
1004 elf_version(EV_CURRENT);
1005
1006 elf = malloc(sizeof(*elf));
1007 if (!elf) {
1008 perror("malloc");
1009 return NULL;
1010 }
1011 memset(elf, 0, sizeof(*elf));
1012
1013 INIT_LIST_HEAD(&elf->sections);
1014
1015 elf->fd = open(name, flags);
1016 if (elf->fd == -1) {
1017 fprintf(stderr, "objtool: Can't open '%s': %s\n",
1018 name, strerror(errno));
1019 goto err;
1020 }
1021
1022 if ((flags & O_ACCMODE) == O_RDONLY)
1023 cmd = ELF_C_READ_MMAP;
1024 else if ((flags & O_ACCMODE) == O_RDWR)
1025 cmd = ELF_C_RDWR;
1026 else /* O_WRONLY */
1027 cmd = ELF_C_WRITE;
1028
1029 elf->elf = elf_begin(elf->fd, cmd, NULL);
1030 if (!elf->elf) {
1031 WARN_ELF("elf_begin");
1032 goto err;
1033 }
1034
1035 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
1036 WARN_ELF("gelf_getehdr");
1037 goto err;
1038 }
1039
1040 if (read_sections(elf))
1041 goto err;
1042
1043 if (read_symbols(elf))
1044 goto err;
1045
1046 if (read_relocs(elf))
1047 goto err;
1048
1049 return elf;
1050
1051err:
1052 elf_close(elf);
1053 return NULL;
1054}
1055
1056static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
1057{
1058 Elf_Data *data;
1059 Elf_Scn *s;
1060 int len;
1061
1062 if (!strtab)
1063 strtab = find_section_by_name(elf, ".strtab");
1064 if (!strtab) {
1065 WARN("can't find .strtab section");
1066 return -1;
1067 }
1068
1069 s = elf_getscn(elf->elf, strtab->idx);
1070 if (!s) {
1071 WARN_ELF("elf_getscn");
1072 return -1;
1073 }
1074
1075 data = elf_newdata(s);
1076 if (!data) {
1077 WARN_ELF("elf_newdata");
1078 return -1;
1079 }
1080
1081 data->d_buf = str;
1082 data->d_size = strlen(str) + 1;
1083 data->d_align = 1;
1084
1085 len = strtab->sh.sh_size;
1086 strtab->sh.sh_size += data->d_size;
1087
1088 mark_sec_changed(elf, strtab, true);
1089
1090 return len;
1091}
1092
1093struct section *elf_create_section(struct elf *elf, const char *name,
1094 size_t entsize, unsigned int nr)
1095{
1096 struct section *sec, *shstrtab;
1097 size_t size = entsize * nr;
1098 Elf_Scn *s;
1099
1100 sec = malloc(sizeof(*sec));
1101 if (!sec) {
1102 perror("malloc");
1103 return NULL;
1104 }
1105 memset(sec, 0, sizeof(*sec));
1106
1107 INIT_LIST_HEAD(&sec->symbol_list);
1108
1109 s = elf_newscn(elf->elf);
1110 if (!s) {
1111 WARN_ELF("elf_newscn");
1112 return NULL;
1113 }
1114
1115 sec->name = strdup(name);
1116 if (!sec->name) {
1117 perror("strdup");
1118 return NULL;
1119 }
1120
1121 sec->idx = elf_ndxscn(s);
1122
1123 sec->data = elf_newdata(s);
1124 if (!sec->data) {
1125 WARN_ELF("elf_newdata");
1126 return NULL;
1127 }
1128
1129 sec->data->d_size = size;
1130 sec->data->d_align = 1;
1131
1132 if (size) {
1133 sec->data->d_buf = malloc(size);
1134 if (!sec->data->d_buf) {
1135 perror("malloc");
1136 return NULL;
1137 }
1138 memset(sec->data->d_buf, 0, size);
1139 }
1140
1141 if (!gelf_getshdr(s, &sec->sh)) {
1142 WARN_ELF("gelf_getshdr");
1143 return NULL;
1144 }
1145
1146 sec->sh.sh_size = size;
1147 sec->sh.sh_entsize = entsize;
1148 sec->sh.sh_type = SHT_PROGBITS;
1149 sec->sh.sh_addralign = 1;
1150 sec->sh.sh_flags = SHF_ALLOC;
1151
1152 /* Add section name to .shstrtab (or .strtab for Clang) */
1153 shstrtab = find_section_by_name(elf, ".shstrtab");
1154 if (!shstrtab)
1155 shstrtab = find_section_by_name(elf, ".strtab");
1156 if (!shstrtab) {
1157 WARN("can't find .shstrtab or .strtab section");
1158 return NULL;
1159 }
1160 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
1161 if (sec->sh.sh_name == -1)
1162 return NULL;
1163
1164 list_add_tail(&sec->list, &elf->sections);
1165 elf_hash_add(section, &sec->hash, sec->idx);
1166 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
1167
1168 mark_sec_changed(elf, sec, true);
1169
1170 return sec;
1171}
1172
1173static struct section *elf_create_rela_section(struct elf *elf,
1174 struct section *sec,
1175 unsigned int reloc_nr)
1176{
1177 struct section *rsec;
1178 char *rsec_name;
1179
1180 rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
1181 if (!rsec_name) {
1182 perror("malloc");
1183 return NULL;
1184 }
1185 strcpy(rsec_name, ".rela");
1186 strcat(rsec_name, sec->name);
1187
1188 rsec = elf_create_section(elf, rsec_name, elf_rela_size(elf), reloc_nr);
1189 free(rsec_name);
1190 if (!rsec)
1191 return NULL;
1192
1193 rsec->data->d_type = ELF_T_RELA;
1194 rsec->sh.sh_type = SHT_RELA;
1195 rsec->sh.sh_addralign = elf_addr_size(elf);
1196 rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1197 rsec->sh.sh_info = sec->idx;
1198 rsec->sh.sh_flags = SHF_INFO_LINK;
1199
1200 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(struct reloc));
1201 if (!rsec->relocs) {
1202 perror("calloc");
1203 return NULL;
1204 }
1205
1206 sec->rsec = rsec;
1207 rsec->base = sec;
1208
1209 return rsec;
1210}
1211
1212struct section *elf_create_section_pair(struct elf *elf, const char *name,
1213 size_t entsize, unsigned int nr,
1214 unsigned int reloc_nr)
1215{
1216 struct section *sec;
1217
1218 sec = elf_create_section(elf, name, entsize, nr);
1219 if (!sec)
1220 return NULL;
1221
1222 if (!elf_create_rela_section(elf, sec, reloc_nr))
1223 return NULL;
1224
1225 return sec;
1226}
1227
1228int elf_write_insn(struct elf *elf, struct section *sec,
1229 unsigned long offset, unsigned int len,
1230 const char *insn)
1231{
1232 Elf_Data *data = sec->data;
1233
1234 if (data->d_type != ELF_T_BYTE || data->d_off) {
1235 WARN("write to unexpected data for section: %s", sec->name);
1236 return -1;
1237 }
1238
1239 memcpy(data->d_buf + offset, insn, len);
1240
1241 mark_sec_changed(elf, sec, true);
1242
1243 return 0;
1244}
1245
1246/*
1247 * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size
1248 * do you:
1249 *
1250 * A) adhere to the section header and truncate the data, or
1251 * B) ignore the section header and write out all the data you've got?
1252 *
1253 * Yes, libelf sucks and we need to manually truncate if we over-allocate data.
1254 */
1255static int elf_truncate_section(struct elf *elf, struct section *sec)
1256{
1257 u64 size = sec->sh.sh_size;
1258 bool truncated = false;
1259 Elf_Data *data = NULL;
1260 Elf_Scn *s;
1261
1262 s = elf_getscn(elf->elf, sec->idx);
1263 if (!s) {
1264 WARN_ELF("elf_getscn");
1265 return -1;
1266 }
1267
1268 for (;;) {
1269 /* get next data descriptor for the relevant section */
1270 data = elf_getdata(s, data);
1271
1272 if (!data) {
1273 if (size) {
1274 WARN("end of section data but non-zero size left\n");
1275 return -1;
1276 }
1277 return 0;
1278 }
1279
1280 if (truncated) {
1281 /* when we remove symbols */
1282 WARN("truncated; but more data\n");
1283 return -1;
1284 }
1285
1286 if (!data->d_size) {
1287 WARN("zero size data");
1288 return -1;
1289 }
1290
1291 if (data->d_size > size) {
1292 truncated = true;
1293 data->d_size = size;
1294 }
1295
1296 size -= data->d_size;
1297 }
1298}
1299
1300int elf_write(struct elf *elf)
1301{
1302 struct section *sec;
1303 Elf_Scn *s;
1304
1305 if (opts.dryrun)
1306 return 0;
1307
1308 /* Update changed relocation sections and section headers: */
1309 list_for_each_entry(sec, &elf->sections, list) {
1310 if (sec->truncate)
1311 elf_truncate_section(elf, sec);
1312
1313 if (sec_changed(sec)) {
1314 s = elf_getscn(elf->elf, sec->idx);
1315 if (!s) {
1316 WARN_ELF("elf_getscn");
1317 return -1;
1318 }
1319
1320 /* Note this also flags the section dirty */
1321 if (!gelf_update_shdr(s, &sec->sh)) {
1322 WARN_ELF("gelf_update_shdr");
1323 return -1;
1324 }
1325
1326 mark_sec_changed(elf, sec, false);
1327 }
1328 }
1329
1330 /* Make sure the new section header entries get updated properly. */
1331 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1332
1333 /* Write all changes to the file. */
1334 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1335 WARN_ELF("elf_update");
1336 return -1;
1337 }
1338
1339 elf->changed = false;
1340
1341 return 0;
1342}
1343
1344void elf_close(struct elf *elf)
1345{
1346 if (elf->elf)
1347 elf_end(elf->elf);
1348
1349 if (elf->fd > 0)
1350 close(elf->fd);
1351
1352 /*
1353 * NOTE: All remaining allocations are leaked on purpose. Objtool is
1354 * about to exit anyway.
1355 */
1356}