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 int eprintf(int level, int var, const char *fmt, ...)
119 {
120 va_list args;
121 int ret;
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 /*
262 * The data of compressed section should be aligned to 4
263 * (for 32bit) or 8 (for 64 bit) bytes. The binutils ld
264 * sets sh_addralign to 1, which makes libelf fail with
265 * misaligned section error during the update:
266 * FAILED elf_update(WRITE): invalid section alignment
267 *
268 * While waiting for ld fix, we fix the compressed sections
269 * sh_addralign value manualy.
270 */
compressed_section_fix(Elf * elf,Elf_Scn * scn,GElf_Shdr * sh)271 static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
272 {
273 int expected = gelf_getclass(elf) == ELFCLASS32 ? 4 : 8;
274
275 if (!(sh->sh_flags & SHF_COMPRESSED))
276 return 0;
277
278 if (sh->sh_addralign == expected)
279 return 0;
280
281 pr_debug2(" - fixing wrong alignment sh_addralign %u, expected %u\n",
282 sh->sh_addralign, expected);
283
284 sh->sh_addralign = expected;
285
286 if (gelf_update_shdr(scn, sh) == 0) {
287 printf("FAILED cannot update section header: %s\n",
288 elf_errmsg(-1));
289 return -1;
290 }
291 return 0;
292 }
293
elf_collect(struct object * obj)294 static int elf_collect(struct object *obj)
295 {
296 Elf_Scn *scn = NULL;
297 size_t shdrstrndx;
298 int idx = 0;
299 Elf *elf;
300 int fd;
301
302 fd = open(obj->path, O_RDWR, 0666);
303 if (fd == -1) {
304 pr_err("FAILED cannot open %s: %s\n",
305 obj->path, strerror(errno));
306 return -1;
307 }
308
309 elf_version(EV_CURRENT);
310
311 elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
312 if (!elf) {
313 pr_err("FAILED cannot create ELF descriptor: %s\n",
314 elf_errmsg(-1));
315 return -1;
316 }
317
318 obj->efile.fd = fd;
319 obj->efile.elf = elf;
320
321 elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT);
322
323 if (elf_getshdrstrndx(elf, &shdrstrndx) != 0) {
324 pr_err("FAILED cannot get shdr str ndx\n");
325 return -1;
326 }
327
328 /*
329 * Scan all the elf sections and look for save data
330 * from .BTF_ids section and symbols.
331 */
332 while ((scn = elf_nextscn(elf, scn)) != NULL) {
333 Elf_Data *data;
334 GElf_Shdr sh;
335 char *name;
336
337 idx++;
338 if (gelf_getshdr(scn, &sh) != &sh) {
339 pr_err("FAILED get section(%d) header\n", idx);
340 return -1;
341 }
342
343 name = elf_strptr(elf, shdrstrndx, sh.sh_name);
344 if (!name) {
345 pr_err("FAILED get section(%d) name\n", idx);
346 return -1;
347 }
348
349 data = elf_getdata(scn, 0);
350 if (!data) {
351 pr_err("FAILED to get section(%d) data from %s\n",
352 idx, name);
353 return -1;
354 }
355
356 pr_debug2("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
357 idx, name, (unsigned long) data->d_size,
358 (int) sh.sh_link, (unsigned long) sh.sh_flags,
359 (int) sh.sh_type);
360
361 if (sh.sh_type == SHT_SYMTAB) {
362 obj->efile.symbols = data;
363 obj->efile.symbols_shndx = idx;
364 obj->efile.strtabidx = sh.sh_link;
365 } else if (!strcmp(name, BTF_IDS_SECTION)) {
366 obj->efile.idlist = data;
367 obj->efile.idlist_shndx = idx;
368 obj->efile.idlist_addr = sh.sh_addr;
369 }
370
371 if (compressed_section_fix(elf, scn, &sh))
372 return -1;
373 }
374
375 return 0;
376 }
377
symbols_collect(struct object * obj)378 static int symbols_collect(struct object *obj)
379 {
380 Elf_Scn *scn = NULL;
381 int n, i, err = 0;
382 GElf_Shdr sh;
383 char *name;
384
385 scn = elf_getscn(obj->efile.elf, obj->efile.symbols_shndx);
386 if (!scn)
387 return -1;
388
389 if (gelf_getshdr(scn, &sh) != &sh)
390 return -1;
391
392 n = sh.sh_size / sh.sh_entsize;
393
394 /*
395 * Scan symbols and look for the ones starting with
396 * __BTF_ID__* over .BTF_ids section.
397 */
398 for (i = 0; !err && i < n; i++) {
399 char *tmp, *prefix;
400 struct btf_id *id;
401 GElf_Sym sym;
402 int err = -1;
403
404 if (!gelf_getsym(obj->efile.symbols, i, &sym))
405 return -1;
406
407 if (sym.st_shndx != obj->efile.idlist_shndx)
408 continue;
409
410 name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
411 sym.st_name);
412
413 if (!is_btf_id(name))
414 continue;
415
416 /*
417 * __BTF_ID__TYPE__vfs_truncate__0
418 * prefix = ^
419 */
420 prefix = name + sizeof(BTF_ID) - 1;
421
422 /* struct */
423 if (!strncmp(prefix, BTF_STRUCT, sizeof(BTF_STRUCT) - 1)) {
424 obj->nr_structs++;
425 id = add_symbol(&obj->structs, prefix, sizeof(BTF_STRUCT) - 1);
426 /* union */
427 } else if (!strncmp(prefix, BTF_UNION, sizeof(BTF_UNION) - 1)) {
428 obj->nr_unions++;
429 id = add_symbol(&obj->unions, prefix, sizeof(BTF_UNION) - 1);
430 /* typedef */
431 } else if (!strncmp(prefix, BTF_TYPEDEF, sizeof(BTF_TYPEDEF) - 1)) {
432 obj->nr_typedefs++;
433 id = add_symbol(&obj->typedefs, prefix, sizeof(BTF_TYPEDEF) - 1);
434 /* func */
435 } else if (!strncmp(prefix, BTF_FUNC, sizeof(BTF_FUNC) - 1)) {
436 obj->nr_funcs++;
437 id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
438 /* set */
439 } else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
440 id = add_set(obj, prefix);
441 /*
442 * SET objects store list's count, which is encoded
443 * in symbol's size, together with 'cnt' field hence
444 * that - 1.
445 */
446 if (id)
447 id->cnt = sym.st_size / sizeof(int) - 1;
448 } else {
449 pr_err("FAILED unsupported prefix %s\n", prefix);
450 return -1;
451 }
452
453 if (!id)
454 return -ENOMEM;
455
456 if (id->addr_cnt >= ADDR_CNT) {
457 pr_err("FAILED symbol %s crossed the number of allowed lists",
458 id->name);
459 return -1;
460 }
461 id->addr[id->addr_cnt++] = sym.st_value;
462 }
463
464 return 0;
465 }
466
symbols_resolve(struct object * obj)467 static int symbols_resolve(struct object *obj)
468 {
469 int nr_typedefs = obj->nr_typedefs;
470 int nr_structs = obj->nr_structs;
471 int nr_unions = obj->nr_unions;
472 int nr_funcs = obj->nr_funcs;
473 int err, type_id;
474 struct btf *btf;
475 __u32 nr;
476
477 btf = btf__parse(obj->btf ?: obj->path, NULL);
478 err = libbpf_get_error(btf);
479 if (err) {
480 pr_err("FAILED: load BTF from %s: %s",
481 obj->path, strerror(err));
482 return -1;
483 }
484
485 err = -1;
486 nr = btf__get_nr_types(btf);
487
488 /*
489 * Iterate all the BTF types and search for collected symbol IDs.
490 */
491 for (type_id = 1; type_id <= nr; type_id++) {
492 const struct btf_type *type;
493 struct rb_root *root;
494 struct btf_id *id;
495 const char *str;
496 int *nr;
497
498 type = btf__type_by_id(btf, type_id);
499 if (!type) {
500 pr_err("FAILED: malformed BTF, can't resolve type for ID %d\n",
501 type_id);
502 goto out;
503 }
504
505 if (btf_is_func(type) && nr_funcs) {
506 nr = &nr_funcs;
507 root = &obj->funcs;
508 } else if (btf_is_struct(type) && nr_structs) {
509 nr = &nr_structs;
510 root = &obj->structs;
511 } else if (btf_is_union(type) && nr_unions) {
512 nr = &nr_unions;
513 root = &obj->unions;
514 } else if (btf_is_typedef(type) && nr_typedefs) {
515 nr = &nr_typedefs;
516 root = &obj->typedefs;
517 } else
518 continue;
519
520 str = btf__name_by_offset(btf, type->name_off);
521 if (!str) {
522 pr_err("FAILED: malformed BTF, can't resolve name for ID %d\n",
523 type_id);
524 goto out;
525 }
526
527 id = btf_id__find(root, str);
528 if (id) {
529 id->id = type_id;
530 (*nr)--;
531 }
532 }
533
534 err = 0;
535 out:
536 btf__free(btf);
537 return err;
538 }
539
id_patch(struct object * obj,struct btf_id * id)540 static int id_patch(struct object *obj, struct btf_id *id)
541 {
542 Elf_Data *data = obj->efile.idlist;
543 int *ptr = data->d_buf;
544 int i;
545
546 if (!id->id) {
547 pr_err("FAILED unresolved symbol %s\n", id->name);
548 return -EINVAL;
549 }
550
551 for (i = 0; i < id->addr_cnt; i++) {
552 unsigned long addr = id->addr[i];
553 unsigned long idx = addr - obj->efile.idlist_addr;
554
555 pr_debug("patching addr %5lu: ID %7d [%s]\n",
556 idx, id->id, id->name);
557
558 if (idx >= data->d_size) {
559 pr_err("FAILED patching index %lu out of bounds %lu\n",
560 idx, data->d_size);
561 return -1;
562 }
563
564 idx = idx / sizeof(int);
565 ptr[idx] = id->id;
566 }
567
568 return 0;
569 }
570
__symbols_patch(struct object * obj,struct rb_root * root)571 static int __symbols_patch(struct object *obj, struct rb_root *root)
572 {
573 struct rb_node *next;
574 struct btf_id *id;
575
576 next = rb_first(root);
577 while (next) {
578 id = rb_entry(next, struct btf_id, rb_node);
579
580 if (id_patch(obj, id))
581 return -1;
582
583 next = rb_next(next);
584 }
585 return 0;
586 }
587
cmp_id(const void * pa,const void * pb)588 static int cmp_id(const void *pa, const void *pb)
589 {
590 const int *a = pa, *b = pb;
591
592 return *a - *b;
593 }
594
sets_patch(struct object * obj)595 static int sets_patch(struct object *obj)
596 {
597 Elf_Data *data = obj->efile.idlist;
598 int *ptr = data->d_buf;
599 struct rb_node *next;
600
601 next = rb_first(&obj->sets);
602 while (next) {
603 unsigned long addr, idx;
604 struct btf_id *id;
605 int *base;
606 int cnt;
607
608 id = rb_entry(next, struct btf_id, rb_node);
609 addr = id->addr[0];
610 idx = addr - obj->efile.idlist_addr;
611
612 /* sets are unique */
613 if (id->addr_cnt != 1) {
614 pr_err("FAILED malformed data for set '%s'\n",
615 id->name);
616 return -1;
617 }
618
619 idx = idx / sizeof(int);
620 base = &ptr[idx] + 1;
621 cnt = ptr[idx];
622
623 pr_debug("sorting addr %5lu: cnt %6d [%s]\n",
624 (idx + 1) * sizeof(int), cnt, id->name);
625
626 qsort(base, cnt, sizeof(int), cmp_id);
627
628 next = rb_next(next);
629 }
630 return 0;
631 }
632
symbols_patch(struct object * obj)633 static int symbols_patch(struct object *obj)
634 {
635 int err;
636
637 if (__symbols_patch(obj, &obj->structs) ||
638 __symbols_patch(obj, &obj->unions) ||
639 __symbols_patch(obj, &obj->typedefs) ||
640 __symbols_patch(obj, &obj->funcs) ||
641 __symbols_patch(obj, &obj->sets))
642 return -1;
643
644 if (sets_patch(obj))
645 return -1;
646
647 elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY);
648
649 err = elf_update(obj->efile.elf, ELF_C_WRITE);
650 if (err < 0) {
651 pr_err("FAILED elf_update(WRITE): %s\n",
652 elf_errmsg(-1));
653 }
654
655 pr_debug("update %s for %s\n",
656 err >= 0 ? "ok" : "failed", obj->path);
657 return err < 0 ? -1 : 0;
658 }
659
660 static const char * const resolve_btfids_usage[] = {
661 "resolve_btfids [<options>] <ELF object>",
662 NULL
663 };
664
main(int argc,const char ** argv)665 int main(int argc, const char **argv)
666 {
667 bool no_fail = false;
668 struct object obj = {
669 .efile = {
670 .idlist_shndx = -1,
671 .symbols_shndx = -1,
672 },
673 .structs = RB_ROOT,
674 .unions = RB_ROOT,
675 .typedefs = RB_ROOT,
676 .funcs = RB_ROOT,
677 .sets = RB_ROOT,
678 };
679 struct option btfid_options[] = {
680 OPT_INCR('v', "verbose", &verbose,
681 "be more verbose (show errors, etc)"),
682 OPT_STRING(0, "btf", &obj.btf, "BTF data",
683 "BTF data"),
684 OPT_BOOLEAN(0, "no-fail", &no_fail,
685 "do not fail if " BTF_IDS_SECTION " section is not found"),
686 OPT_END()
687 };
688 int err = -1;
689
690 argc = parse_options(argc, argv, btfid_options, resolve_btfids_usage,
691 PARSE_OPT_STOP_AT_NON_OPTION);
692 if (argc != 1)
693 usage_with_options(resolve_btfids_usage, btfid_options);
694
695 obj.path = argv[0];
696
697 if (elf_collect(&obj))
698 goto out;
699
700 /*
701 * We did not find .BTF_ids section or symbols section,
702 * nothing to do..
703 */
704 if (obj.efile.idlist_shndx == -1 ||
705 obj.efile.symbols_shndx == -1) {
706 if (no_fail)
707 return 0;
708 pr_err("FAILED to find needed sections\n");
709 return -1;
710 }
711
712 if (symbols_collect(&obj))
713 goto out;
714
715 if (symbols_resolve(&obj))
716 goto out;
717
718 if (symbols_patch(&obj))
719 goto out;
720
721 err = 0;
722 out:
723 if (obj.efile.elf)
724 elf_end(obj.efile.elf);
725 close(obj.efile.fd);
726 return err;
727 }
728
