1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2
3 /*
4 * resolve_btfids scans Elf object for .BTF_ids section and resolves
5 * its symbols with BTF ID values.
6 *
7 * Each symbol points to 4 bytes data and is expected to have
8 * following name syntax:
9 *
10 * __BTF_ID__<type>__<symbol>[__<id>]
11 *
12 * type is:
13 *
14 * func - lookup BTF_KIND_FUNC symbol with <symbol> name
15 * and store its ID into the data:
16 *
17 * __BTF_ID__func__vfs_close__1:
18 * .zero 4
19 *
20 * struct - lookup BTF_KIND_STRUCT symbol with <symbol> name
21 * and store its ID into the data:
22 *
23 * __BTF_ID__struct__sk_buff__1:
24 * .zero 4
25 *
26 * union - lookup BTF_KIND_UNION symbol with <symbol> name
27 * and store its ID into the data:
28 *
29 * __BTF_ID__union__thread_union__1:
30 * .zero 4
31 *
32 * typedef - lookup BTF_KIND_TYPEDEF symbol with <symbol> name
33 * and store its ID into the data:
34 *
35 * __BTF_ID__typedef__pid_t__1:
36 * .zero 4
37 *
38 * set - store symbol size into first 4 bytes and sort following
39 * ID list
40 *
41 * __BTF_ID__set__list:
42 * .zero 4
43 * list:
44 * __BTF_ID__func__vfs_getattr__3:
45 * .zero 4
46 * __BTF_ID__func__vfs_fallocate__4:
47 * .zero 4
48 */
49
50 #define _GNU_SOURCE
51 #include <stdio.h>
52 #include <string.h>
53 #include <unistd.h>
54 #include <stdlib.h>
55 #include <libelf.h>
56 #include <gelf.h>
57 #include <sys/stat.h>
58 #include <fcntl.h>
59 #include <errno.h>
60 #include <linux/rbtree.h>
61 #include <linux/zalloc.h>
62 #include <linux/err.h>
63 #include <btf.h>
64 #include <libbpf.h>
65 #include <parse-options.h>
66
67 #define BTF_IDS_SECTION ".BTF_ids"
68 #define BTF_ID "__BTF_ID__"
69
70 #define BTF_STRUCT "struct"
71 #define BTF_UNION "union"
72 #define BTF_TYPEDEF "typedef"
73 #define BTF_FUNC "func"
74 #define BTF_SET "set"
75
76 #define ADDR_CNT 100
77
78 struct btf_id {
79 struct rb_node rb_node;
80 char *name;
81 union {
82 int id;
83 int cnt;
84 };
85 int addr_cnt;
86 Elf64_Addr addr[ADDR_CNT];
87 };
88
89 struct object {
90 const char *path;
91 const char *btf;
92
93 struct {
94 int fd;
95 Elf *elf;
96 Elf_Data *symbols;
97 Elf_Data *idlist;
98 int symbols_shndx;
99 int idlist_shndx;
100 size_t strtabidx;
101 unsigned long idlist_addr;
102 } efile;
103
104 struct rb_root sets;
105 struct rb_root structs;
106 struct rb_root unions;
107 struct rb_root typedefs;
108 struct rb_root funcs;
109
110 int nr_funcs;
111 int nr_structs;
112 int nr_unions;
113 int nr_typedefs;
114 };
115
116 static int verbose;
117
eprintf(int level,int var,const char * fmt,...)118 static int eprintf(int level, int var, const char *fmt, ...)
119 {
120 va_list args;
121 int ret = 0;
122
123 if (var >= level) {
124 va_start(args, fmt);
125 ret = vfprintf(stderr, fmt, args);
126 va_end(args);
127 }
128 return ret;
129 }
130
131 #ifndef pr_fmt
132 #define pr_fmt(fmt) fmt
133 #endif
134
135 #define pr_debug(fmt, ...) \
136 eprintf(1, verbose, pr_fmt(fmt), ##__VA_ARGS__)
137 #define pr_debugN(n, fmt, ...) \
138 eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__)
139 #define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
140 #define pr_err(fmt, ...) \
141 eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
142
is_btf_id(const char * name)143 static bool is_btf_id(const char *name)
144 {
145 return name && !strncmp(name, BTF_ID, sizeof(BTF_ID) - 1);
146 }
147
btf_id__find(struct rb_root * root,const char * name)148 static struct btf_id *btf_id__find(struct rb_root *root, const char *name)
149 {
150 struct rb_node *p = root->rb_node;
151 struct btf_id *id;
152 int cmp;
153
154 while (p) {
155 id = rb_entry(p, struct btf_id, rb_node);
156 cmp = strcmp(id->name, name);
157 if (cmp < 0)
158 p = p->rb_left;
159 else if (cmp > 0)
160 p = p->rb_right;
161 else
162 return id;
163 }
164 return NULL;
165 }
166
167 static struct btf_id*
btf_id__add(struct rb_root * root,char * name,bool unique)168 btf_id__add(struct rb_root *root, char *name, bool unique)
169 {
170 struct rb_node **p = &root->rb_node;
171 struct rb_node *parent = NULL;
172 struct btf_id *id;
173 int cmp;
174
175 while (*p != NULL) {
176 parent = *p;
177 id = rb_entry(parent, struct btf_id, rb_node);
178 cmp = strcmp(id->name, name);
179 if (cmp < 0)
180 p = &(*p)->rb_left;
181 else if (cmp > 0)
182 p = &(*p)->rb_right;
183 else
184 return unique ? NULL : id;
185 }
186
187 id = zalloc(sizeof(*id));
188 if (id) {
189 pr_debug("adding symbol %s\n", name);
190 id->name = name;
191 rb_link_node(&id->rb_node, parent, p);
192 rb_insert_color(&id->rb_node, root);
193 }
194 return id;
195 }
196
get_id(const char * prefix_end)197 static char *get_id(const char *prefix_end)
198 {
199 /*
200 * __BTF_ID__func__vfs_truncate__0
201 * prefix_end = ^
202 * pos = ^
203 */
204 int len = strlen(prefix_end);
205 int pos = sizeof("__") - 1;
206 char *p, *id;
207
208 if (pos >= len)
209 return NULL;
210
211 id = strdup(prefix_end + pos);
212 if (id) {
213 /*
214 * __BTF_ID__func__vfs_truncate__0
215 * id = ^
216 *
217 * cut the unique id part
218 */
219 p = strrchr(id, '_');
220 p--;
221 if (*p != '_') {
222 free(id);
223 return NULL;
224 }
225 *p = '\0';
226 }
227 return id;
228 }
229
add_set(struct object * obj,char * name)230 static struct btf_id *add_set(struct object *obj, char *name)
231 {
232 /*
233 * __BTF_ID__set__name
234 * name = ^
235 * id = ^
236 */
237 char *id = name + sizeof(BTF_SET "__") - 1;
238 int len = strlen(name);
239
240 if (id >= name + len) {
241 pr_err("FAILED to parse set name: %s\n", name);
242 return NULL;
243 }
244
245 return btf_id__add(&obj->sets, id, true);
246 }
247
add_symbol(struct rb_root * root,char * name,size_t size)248 static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
249 {
250 char *id;
251
252 id = get_id(name + size);
253 if (!id) {
254 pr_err("FAILED to parse symbol name: %s\n", name);
255 return NULL;
256 }
257
258 return btf_id__add(root, id, false);
259 }
260
261 /* Older libelf.h and glibc elf.h might not yet define the ELF compression types. */
262 #ifndef SHF_COMPRESSED
263 #define SHF_COMPRESSED (1 << 11) /* Section with compressed data. */
264 #endif
265
266 /*
267 * The data of compressed section should be aligned to 4
268 * (for 32bit) or 8 (for 64 bit) bytes. The binutils ld
269 * sets sh_addralign to 1, which makes libelf fail with
270 * misaligned section error during the update:
271 * FAILED elf_update(WRITE): invalid section alignment
272 *
273 * While waiting for ld fix, we fix the compressed sections
274 * sh_addralign value manualy.
275 */
compressed_section_fix(Elf * elf,Elf_Scn * scn,GElf_Shdr * sh)276 static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
277 {
278 int expected = gelf_getclass(elf) == ELFCLASS32 ? 4 : 8;
279
280 if (!(sh->sh_flags & SHF_COMPRESSED))
281 return 0;
282
283 if (sh->sh_addralign == expected)
284 return 0;
285
286 pr_debug2(" - fixing wrong alignment sh_addralign %u, expected %u\n",
287 sh->sh_addralign, expected);
288
289 sh->sh_addralign = expected;
290
291 if (gelf_update_shdr(scn, sh) == 0) {
292 printf("FAILED cannot update section header: %s\n",
293 elf_errmsg(-1));
294 return -1;
295 }
296 return 0;
297 }
298
elf_collect(struct object * obj)299 static int elf_collect(struct object *obj)
300 {
301 Elf_Scn *scn = NULL;
302 size_t shdrstrndx;
303 int idx = 0;
304 Elf *elf;
305 int fd;
306
307 fd = open(obj->path, O_RDWR, 0666);
308 if (fd == -1) {
309 pr_err("FAILED cannot open %s: %s\n",
310 obj->path, strerror(errno));
311 return -1;
312 }
313
314 elf_version(EV_CURRENT);
315
316 elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
317 if (!elf) {
318 pr_err("FAILED cannot create ELF descriptor: %s\n",
319 elf_errmsg(-1));
320 return -1;
321 }
322
323 obj->efile.fd = fd;
324 obj->efile.elf = elf;
325
326 elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT);
327
328 if (elf_getshdrstrndx(elf, &shdrstrndx) != 0) {
329 pr_err("FAILED cannot get shdr str ndx\n");
330 return -1;
331 }
332
333 /*
334 * Scan all the elf sections and look for save data
335 * from .BTF_ids section and symbols.
336 */
337 while ((scn = elf_nextscn(elf, scn)) != NULL) {
338 Elf_Data *data;
339 GElf_Shdr sh;
340 char *name;
341
342 idx++;
343 if (gelf_getshdr(scn, &sh) != &sh) {
344 pr_err("FAILED get section(%d) header\n", idx);
345 return -1;
346 }
347
348 name = elf_strptr(elf, shdrstrndx, sh.sh_name);
349 if (!name) {
350 pr_err("FAILED get section(%d) name\n", idx);
351 return -1;
352 }
353
354 data = elf_getdata(scn, 0);
355 if (!data) {
356 pr_err("FAILED to get section(%d) data from %s\n",
357 idx, name);
358 return -1;
359 }
360
361 pr_debug2("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
362 idx, name, (unsigned long) data->d_size,
363 (int) sh.sh_link, (unsigned long) sh.sh_flags,
364 (int) sh.sh_type);
365
366 if (sh.sh_type == SHT_SYMTAB) {
367 obj->efile.symbols = data;
368 obj->efile.symbols_shndx = idx;
369 obj->efile.strtabidx = sh.sh_link;
370 } else if (!strcmp(name, BTF_IDS_SECTION)) {
371 obj->efile.idlist = data;
372 obj->efile.idlist_shndx = idx;
373 obj->efile.idlist_addr = sh.sh_addr;
374 }
375
376 if (compressed_section_fix(elf, scn, &sh))
377 return -1;
378 }
379
380 return 0;
381 }
382
symbols_collect(struct object * obj)383 static int symbols_collect(struct object *obj)
384 {
385 Elf_Scn *scn = NULL;
386 int n, i;
387 GElf_Shdr sh;
388 char *name;
389
390 scn = elf_getscn(obj->efile.elf, obj->efile.symbols_shndx);
391 if (!scn)
392 return -1;
393
394 if (gelf_getshdr(scn, &sh) != &sh)
395 return -1;
396
397 n = sh.sh_size / sh.sh_entsize;
398
399 /*
400 * Scan symbols and look for the ones starting with
401 * __BTF_ID__* over .BTF_ids section.
402 */
403 for (i = 0; i < n; i++) {
404 char *prefix;
405 struct btf_id *id;
406 GElf_Sym sym;
407
408 if (!gelf_getsym(obj->efile.symbols, i, &sym))
409 return -1;
410
411 if (sym.st_shndx != obj->efile.idlist_shndx)
412 continue;
413
414 name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
415 sym.st_name);
416
417 if (!is_btf_id(name))
418 continue;
419
420 /*
421 * __BTF_ID__TYPE__vfs_truncate__0
422 * prefix = ^
423 */
424 prefix = name + sizeof(BTF_ID) - 1;
425
426 /* struct */
427 if (!strncmp(prefix, BTF_STRUCT, sizeof(BTF_STRUCT) - 1)) {
428 obj->nr_structs++;
429 id = add_symbol(&obj->structs, prefix, sizeof(BTF_STRUCT) - 1);
430 /* union */
431 } else if (!strncmp(prefix, BTF_UNION, sizeof(BTF_UNION) - 1)) {
432 obj->nr_unions++;
433 id = add_symbol(&obj->unions, prefix, sizeof(BTF_UNION) - 1);
434 /* typedef */
435 } else if (!strncmp(prefix, BTF_TYPEDEF, sizeof(BTF_TYPEDEF) - 1)) {
436 obj->nr_typedefs++;
437 id = add_symbol(&obj->typedefs, prefix, sizeof(BTF_TYPEDEF) - 1);
438 /* func */
439 } else if (!strncmp(prefix, BTF_FUNC, sizeof(BTF_FUNC) - 1)) {
440 obj->nr_funcs++;
441 id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
442 /* set */
443 } else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
444 id = add_set(obj, prefix);
445 /*
446 * SET objects store list's count, which is encoded
447 * in symbol's size, together with 'cnt' field hence
448 * that - 1.
449 */
450 if (id)
451 id->cnt = sym.st_size / sizeof(int) - 1;
452 } else {
453 pr_err("FAILED unsupported prefix %s\n", prefix);
454 return -1;
455 }
456
457 if (!id)
458 return -ENOMEM;
459
460 if (id->addr_cnt >= ADDR_CNT) {
461 pr_err("FAILED symbol %s crossed the number of allowed lists",
462 id->name);
463 return -1;
464 }
465 id->addr[id->addr_cnt++] = sym.st_value;
466 }
467
468 return 0;
469 }
470
symbols_resolve(struct object * obj)471 static int symbols_resolve(struct object *obj)
472 {
473 int nr_typedefs = obj->nr_typedefs;
474 int nr_structs = obj->nr_structs;
475 int nr_unions = obj->nr_unions;
476 int nr_funcs = obj->nr_funcs;
477 int err, type_id;
478 struct btf *btf;
479 __u32 nr;
480
481 btf = btf__parse(obj->btf ?: obj->path, NULL);
482 err = libbpf_get_error(btf);
483 if (err) {
484 pr_err("FAILED: load BTF from %s: %s",
485 obj->path, strerror(err));
486 return -1;
487 }
488
489 err = -1;
490 nr = btf__get_nr_types(btf);
491
492 /*
493 * Iterate all the BTF types and search for collected symbol IDs.
494 */
495 for (type_id = 1; type_id <= nr; type_id++) {
496 const struct btf_type *type;
497 struct rb_root *root;
498 struct btf_id *id;
499 const char *str;
500 int *nr;
501
502 type = btf__type_by_id(btf, type_id);
503 if (!type) {
504 pr_err("FAILED: malformed BTF, can't resolve type for ID %d\n",
505 type_id);
506 goto out;
507 }
508
509 if (btf_is_func(type) && nr_funcs) {
510 nr = &nr_funcs;
511 root = &obj->funcs;
512 } else if (btf_is_struct(type) && nr_structs) {
513 nr = &nr_structs;
514 root = &obj->structs;
515 } else if (btf_is_union(type) && nr_unions) {
516 nr = &nr_unions;
517 root = &obj->unions;
518 } else if (btf_is_typedef(type) && nr_typedefs) {
519 nr = &nr_typedefs;
520 root = &obj->typedefs;
521 } else
522 continue;
523
524 str = btf__name_by_offset(btf, type->name_off);
525 if (!str) {
526 pr_err("FAILED: malformed BTF, can't resolve name for ID %d\n",
527 type_id);
528 goto out;
529 }
530
531 id = btf_id__find(root, str);
532 if (id) {
533 id->id = type_id;
534 (*nr)--;
535 }
536 }
537
538 err = 0;
539 out:
540 btf__free(btf);
541 return err;
542 }
543
id_patch(struct object * obj,struct btf_id * id)544 static int id_patch(struct object *obj, struct btf_id *id)
545 {
546 Elf_Data *data = obj->efile.idlist;
547 int *ptr = data->d_buf;
548 int i;
549
550 if (!id->id) {
551 pr_err("FAILED unresolved symbol %s\n", id->name);
552 return -EINVAL;
553 }
554
555 for (i = 0; i < id->addr_cnt; i++) {
556 unsigned long addr = id->addr[i];
557 unsigned long idx = addr - obj->efile.idlist_addr;
558
559 pr_debug("patching addr %5lu: ID %7d [%s]\n",
560 idx, id->id, id->name);
561
562 if (idx >= data->d_size) {
563 pr_err("FAILED patching index %lu out of bounds %lu\n",
564 idx, data->d_size);
565 return -1;
566 }
567
568 idx = idx / sizeof(int);
569 ptr[idx] = id->id;
570 }
571
572 return 0;
573 }
574
__symbols_patch(struct object * obj,struct rb_root * root)575 static int __symbols_patch(struct object *obj, struct rb_root *root)
576 {
577 struct rb_node *next;
578 struct btf_id *id;
579
580 next = rb_first(root);
581 while (next) {
582 id = rb_entry(next, struct btf_id, rb_node);
583
584 if (id_patch(obj, id))
585 return -1;
586
587 next = rb_next(next);
588 }
589 return 0;
590 }
591
cmp_id(const void * pa,const void * pb)592 static int cmp_id(const void *pa, const void *pb)
593 {
594 const int *a = pa, *b = pb;
595
596 return *a - *b;
597 }
598
sets_patch(struct object * obj)599 static int sets_patch(struct object *obj)
600 {
601 Elf_Data *data = obj->efile.idlist;
602 int *ptr = data->d_buf;
603 struct rb_node *next;
604
605 next = rb_first(&obj->sets);
606 while (next) {
607 unsigned long addr, idx;
608 struct btf_id *id;
609 int *base;
610 int cnt;
611
612 id = rb_entry(next, struct btf_id, rb_node);
613 addr = id->addr[0];
614 idx = addr - obj->efile.idlist_addr;
615
616 /* sets are unique */
617 if (id->addr_cnt != 1) {
618 pr_err("FAILED malformed data for set '%s'\n",
619 id->name);
620 return -1;
621 }
622
623 idx = idx / sizeof(int);
624 base = &ptr[idx] + 1;
625 cnt = ptr[idx];
626
627 pr_debug("sorting addr %5lu: cnt %6d [%s]\n",
628 (idx + 1) * sizeof(int), cnt, id->name);
629
630 qsort(base, cnt, sizeof(int), cmp_id);
631
632 next = rb_next(next);
633 }
634 return 0;
635 }
636
symbols_patch(struct object * obj)637 static int symbols_patch(struct object *obj)
638 {
639 int err;
640
641 if (__symbols_patch(obj, &obj->structs) ||
642 __symbols_patch(obj, &obj->unions) ||
643 __symbols_patch(obj, &obj->typedefs) ||
644 __symbols_patch(obj, &obj->funcs) ||
645 __symbols_patch(obj, &obj->sets))
646 return -1;
647
648 if (sets_patch(obj))
649 return -1;
650
651 /* Set type to ensure endian translation occurs. */
652 obj->efile.idlist->d_type = ELF_T_WORD;
653
654 elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY);
655
656 err = elf_update(obj->efile.elf, ELF_C_WRITE);
657 if (err < 0) {
658 pr_err("FAILED elf_update(WRITE): %s\n",
659 elf_errmsg(-1));
660 }
661
662 pr_debug("update %s for %s\n",
663 err >= 0 ? "ok" : "failed", obj->path);
664 return err < 0 ? -1 : 0;
665 }
666
667 static const char * const resolve_btfids_usage[] = {
668 "resolve_btfids [<options>] <ELF object>",
669 NULL
670 };
671
main(int argc,const char ** argv)672 int main(int argc, const char **argv)
673 {
674 bool no_fail = false;
675 struct object obj = {
676 .efile = {
677 .idlist_shndx = -1,
678 .symbols_shndx = -1,
679 },
680 .structs = RB_ROOT,
681 .unions = RB_ROOT,
682 .typedefs = RB_ROOT,
683 .funcs = RB_ROOT,
684 .sets = RB_ROOT,
685 };
686 struct option btfid_options[] = {
687 OPT_INCR('v', "verbose", &verbose,
688 "be more verbose (show errors, etc)"),
689 OPT_STRING(0, "btf", &obj.btf, "BTF data",
690 "BTF data"),
691 OPT_BOOLEAN(0, "no-fail", &no_fail,
692 "do not fail if " BTF_IDS_SECTION " section is not found"),
693 OPT_END()
694 };
695 int err = -1;
696
697 argc = parse_options(argc, argv, btfid_options, resolve_btfids_usage,
698 PARSE_OPT_STOP_AT_NON_OPTION);
699 if (argc != 1)
700 usage_with_options(resolve_btfids_usage, btfid_options);
701
702 obj.path = argv[0];
703
704 if (elf_collect(&obj))
705 goto out;
706
707 /*
708 * We did not find .BTF_ids section or symbols section,
709 * nothing to do..
710 */
711 if (obj.efile.idlist_shndx == -1 ||
712 obj.efile.symbols_shndx == -1) {
713 if (no_fail)
714 return 0;
715 pr_err("FAILED to find needed sections\n");
716 return -1;
717 }
718
719 if (symbols_collect(&obj))
720 goto out;
721
722 if (symbols_resolve(&obj))
723 goto out;
724
725 if (symbols_patch(&obj))
726 goto out;
727
728 err = 0;
729 out:
730 if (obj.efile.elf)
731 elf_end(obj.efile.elf);
732 close(obj.efile.fd);
733 return err;
734 }
735