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1// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2
3#ifndef _GNU_SOURCE
4#define _GNU_SOURCE
5#endif
6#include <libelf.h>
7#include <gelf.h>
8#include <fcntl.h>
9#include <linux/kernel.h>
10
11#include "libbpf_internal.h"
12
13/* A SHT_GNU_versym section holds 16-bit words. This bit is set if
14 * the symbol is hidden and can only be seen when referenced using an
15 * explicit version number. This is a GNU extension.
16 */
17#define VERSYM_HIDDEN 0x8000
18
19/* This is the mask for the rest of the data in a word read from a
20 * SHT_GNU_versym section.
21 */
22#define VERSYM_VERSION 0x7fff
23
24int elf_open(const char *binary_path, struct elf_fd *elf_fd)
25{
26 int fd, ret;
27 Elf *elf;
28
29 elf_fd->elf = NULL;
30 elf_fd->fd = -1;
31
32 if (elf_version(EV_CURRENT) == EV_NONE) {
33 pr_warn("elf: failed to init libelf for %s\n", binary_path);
34 return -LIBBPF_ERRNO__LIBELF;
35 }
36 fd = open(binary_path, O_RDONLY | O_CLOEXEC);
37 if (fd < 0) {
38 ret = -errno;
39 pr_warn("elf: failed to open %s: %s\n", binary_path, errstr(ret));
40 return ret;
41 }
42 elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
43 if (!elf) {
44 pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
45 close(fd);
46 return -LIBBPF_ERRNO__FORMAT;
47 }
48 elf_fd->fd = fd;
49 elf_fd->elf = elf;
50 return 0;
51}
52
53void elf_close(struct elf_fd *elf_fd)
54{
55 if (!elf_fd)
56 return;
57 elf_end(elf_fd->elf);
58 close(elf_fd->fd);
59}
60
61/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
62static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
63{
64 while ((scn = elf_nextscn(elf, scn)) != NULL) {
65 GElf_Shdr sh;
66
67 if (!gelf_getshdr(scn, &sh))
68 continue;
69 if (sh.sh_type == sh_type)
70 return scn;
71 }
72 return NULL;
73}
74
75struct elf_sym {
76 const char *name;
77 GElf_Sym sym;
78 GElf_Shdr sh;
79 int ver;
80 bool hidden;
81};
82
83struct elf_sym_iter {
84 Elf *elf;
85 Elf_Data *syms;
86 Elf_Data *versyms;
87 Elf_Data *verdefs;
88 size_t nr_syms;
89 size_t strtabidx;
90 size_t verdef_strtabidx;
91 size_t next_sym_idx;
92 struct elf_sym sym;
93 int st_type;
94};
95
96static int elf_sym_iter_new(struct elf_sym_iter *iter,
97 Elf *elf, const char *binary_path,
98 int sh_type, int st_type)
99{
100 Elf_Scn *scn = NULL;
101 GElf_Ehdr ehdr;
102 GElf_Shdr sh;
103
104 memset(iter, 0, sizeof(*iter));
105
106 if (!gelf_getehdr(elf, &ehdr)) {
107 pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
108 return -EINVAL;
109 }
110
111 scn = elf_find_next_scn_by_type(elf, sh_type, NULL);
112 if (!scn) {
113 pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
114 binary_path);
115 return -ENOENT;
116 }
117
118 if (!gelf_getshdr(scn, &sh))
119 return -EINVAL;
120
121 iter->strtabidx = sh.sh_link;
122 iter->syms = elf_getdata(scn, 0);
123 if (!iter->syms) {
124 pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
125 binary_path, elf_errmsg(-1));
126 return -EINVAL;
127 }
128 iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
129 iter->elf = elf;
130 iter->st_type = st_type;
131
132 /* Version symbol table is meaningful to dynsym only */
133 if (sh_type != SHT_DYNSYM)
134 return 0;
135
136 scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
137 if (!scn)
138 return 0;
139 iter->versyms = elf_getdata(scn, 0);
140
141 scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
142 if (!scn)
143 return 0;
144
145 iter->verdefs = elf_getdata(scn, 0);
146 if (!iter->verdefs || !gelf_getshdr(scn, &sh)) {
147 pr_warn("elf: failed to get verdef ELF section in '%s'\n", binary_path);
148 return -EINVAL;
149 }
150 iter->verdef_strtabidx = sh.sh_link;
151
152 return 0;
153}
154
155static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
156{
157 struct elf_sym *ret = &iter->sym;
158 GElf_Sym *sym = &ret->sym;
159 const char *name = NULL;
160 GElf_Versym versym;
161 Elf_Scn *sym_scn;
162 size_t idx;
163
164 for (idx = iter->next_sym_idx; idx < iter->nr_syms; idx++) {
165 if (!gelf_getsym(iter->syms, idx, sym))
166 continue;
167 if (GELF_ST_TYPE(sym->st_info) != iter->st_type)
168 continue;
169 name = elf_strptr(iter->elf, iter->strtabidx, sym->st_name);
170 if (!name)
171 continue;
172 sym_scn = elf_getscn(iter->elf, sym->st_shndx);
173 if (!sym_scn)
174 continue;
175 if (!gelf_getshdr(sym_scn, &ret->sh))
176 continue;
177
178 iter->next_sym_idx = idx + 1;
179 ret->name = name;
180 ret->ver = 0;
181 ret->hidden = false;
182
183 if (iter->versyms) {
184 if (!gelf_getversym(iter->versyms, idx, &versym))
185 continue;
186 ret->ver = versym & VERSYM_VERSION;
187 ret->hidden = versym & VERSYM_HIDDEN;
188 }
189 return ret;
190 }
191
192 return NULL;
193}
194
195static const char *elf_get_vername(struct elf_sym_iter *iter, int ver)
196{
197 GElf_Verdaux verdaux;
198 GElf_Verdef verdef;
199 int offset;
200
201 if (!iter->verdefs)
202 return NULL;
203
204 offset = 0;
205 while (gelf_getverdef(iter->verdefs, offset, &verdef)) {
206 if (verdef.vd_ndx != ver) {
207 if (!verdef.vd_next)
208 break;
209
210 offset += verdef.vd_next;
211 continue;
212 }
213
214 if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux))
215 break;
216
217 return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name);
218
219 }
220 return NULL;
221}
222
223static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym,
224 const char *name, size_t name_len, const char *lib_ver)
225{
226 const char *ver_name;
227
228 /* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER
229 * make sure the func part matches the user specified name
230 */
231 if (strncmp(sym->name, name, name_len) != 0)
232 return false;
233
234 /* ...but we don't want a search for "foo" to match 'foo2" also, so any
235 * additional characters in sname should be of the form "@@LIB".
236 */
237 if (sym->name[name_len] != '\0' && sym->name[name_len] != '@')
238 return false;
239
240 /* If user does not specify symbol version, then we got a match */
241 if (!lib_ver)
242 return true;
243
244 /* If user specifies symbol version, for dynamic symbols,
245 * get version name from ELF verdef section for comparison.
246 */
247 if (sh_type == SHT_DYNSYM) {
248 ver_name = elf_get_vername(iter, sym->ver);
249 if (!ver_name)
250 return false;
251 return strcmp(ver_name, lib_ver) == 0;
252 }
253
254 /* For normal symbols, it is already in form of func@LIB_VER */
255 return strcmp(sym->name, name) == 0;
256}
257
258/* Transform symbol's virtual address (absolute for binaries and relative
259 * for shared libs) into file offset, which is what kernel is expecting
260 * for uprobe/uretprobe attachment.
261 * See Documentation/trace/uprobetracer.rst for more details. This is done
262 * by looking up symbol's containing section's header and using iter's virtual
263 * address (sh_addr) and corresponding file offset (sh_offset) to transform
264 * sym.st_value (virtual address) into desired final file offset.
265 */
266static unsigned long elf_sym_offset(struct elf_sym *sym)
267{
268 return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
269}
270
271/* Find offset of function name in the provided ELF object. "binary_path" is
272 * the path to the ELF binary represented by "elf", and only used for error
273 * reporting matters. "name" matches symbol name or name@@LIB for library
274 * functions.
275 */
276long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
277{
278 int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
279 const char *at_symbol, *lib_ver;
280 bool is_shared_lib;
281 long ret = -ENOENT;
282 size_t name_len;
283 GElf_Ehdr ehdr;
284
285 if (!gelf_getehdr(elf, &ehdr)) {
286 pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
287 ret = -LIBBPF_ERRNO__FORMAT;
288 goto out;
289 }
290 /* for shared lib case, we do not need to calculate relative offset */
291 is_shared_lib = ehdr.e_type == ET_DYN;
292
293 /* Does name specify "@@LIB_VER" or "@LIB_VER" ? */
294 at_symbol = strchr(name, '@');
295 if (at_symbol) {
296 name_len = at_symbol - name;
297 /* skip second @ if it's @@LIB_VER case */
298 if (at_symbol[1] == '@')
299 at_symbol++;
300 lib_ver = at_symbol + 1;
301 } else {
302 name_len = strlen(name);
303 lib_ver = NULL;
304 }
305
306 /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
307 * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
308 * linked binary may not have SHT_DYMSYM, so absence of a section should not be
309 * reported as a warning/error.
310 */
311 for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
312 struct elf_sym_iter iter;
313 struct elf_sym *sym;
314 int last_bind = -1;
315 int cur_bind;
316
317 ret = elf_sym_iter_new(&iter, elf, binary_path, sh_types[i], STT_FUNC);
318 if (ret == -ENOENT)
319 continue;
320 if (ret)
321 goto out;
322
323 while ((sym = elf_sym_iter_next(&iter))) {
324 if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver))
325 continue;
326
327 cur_bind = GELF_ST_BIND(sym->sym.st_info);
328
329 if (ret > 0) {
330 /* handle multiple matches */
331 if (elf_sym_offset(sym) == ret) {
332 /* same offset, no problem */
333 continue;
334 } else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
335 /* Only accept one non-weak bind. */
336 pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
337 sym->name, name, binary_path);
338 ret = -LIBBPF_ERRNO__FORMAT;
339 goto out;
340 } else if (cur_bind == STB_WEAK) {
341 /* already have a non-weak bind, and
342 * this is a weak bind, so ignore.
343 */
344 continue;
345 }
346 }
347
348 ret = elf_sym_offset(sym);
349 last_bind = cur_bind;
350 }
351 if (ret > 0)
352 break;
353 }
354
355 if (ret > 0) {
356 pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
357 (unsigned long)ret);
358 } else {
359 if (ret == 0) {
360 pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
361 is_shared_lib ? "should not be 0 in a shared library" :
362 "try using shared library path instead");
363 ret = -ENOENT;
364 } else {
365 pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
366 }
367 }
368out:
369 return ret;
370}
371
372/* Find offset of function name in ELF object specified by path. "name" matches
373 * symbol name or name@@LIB for library functions.
374 */
375long elf_find_func_offset_from_file(const char *binary_path, const char *name)
376{
377 struct elf_fd elf_fd;
378 long ret = -ENOENT;
379
380 ret = elf_open(binary_path, &elf_fd);
381 if (ret)
382 return ret;
383 ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
384 elf_close(&elf_fd);
385 return ret;
386}
387
388struct symbol {
389 const char *name;
390 int bind;
391 int idx;
392};
393
394static int symbol_cmp(const void *a, const void *b)
395{
396 const struct symbol *sym_a = a;
397 const struct symbol *sym_b = b;
398
399 return strcmp(sym_a->name, sym_b->name);
400}
401
402/*
403 * Return offsets in @poffsets for symbols specified in @syms array argument.
404 * On success returns 0 and offsets are returned in allocated array with @cnt
405 * size, that needs to be released by the caller.
406 */
407int elf_resolve_syms_offsets(const char *binary_path, int cnt,
408 const char **syms, unsigned long **poffsets,
409 int st_type)
410{
411 int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
412 int err = 0, i, cnt_done = 0;
413 unsigned long *offsets;
414 struct symbol *symbols;
415 struct elf_fd elf_fd;
416
417 err = elf_open(binary_path, &elf_fd);
418 if (err)
419 return err;
420
421 offsets = calloc(cnt, sizeof(*offsets));
422 symbols = calloc(cnt, sizeof(*symbols));
423
424 if (!offsets || !symbols) {
425 err = -ENOMEM;
426 goto out;
427 }
428
429 for (i = 0; i < cnt; i++) {
430 symbols[i].name = syms[i];
431 symbols[i].idx = i;
432 }
433
434 qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);
435
436 for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
437 struct elf_sym_iter iter;
438 struct elf_sym *sym;
439
440 err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], st_type);
441 if (err == -ENOENT)
442 continue;
443 if (err)
444 goto out;
445
446 while ((sym = elf_sym_iter_next(&iter))) {
447 unsigned long sym_offset = elf_sym_offset(sym);
448 int bind = GELF_ST_BIND(sym->sym.st_info);
449 struct symbol *found, tmp = {
450 .name = sym->name,
451 };
452 unsigned long *offset;
453
454 found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
455 if (!found)
456 continue;
457
458 offset = &offsets[found->idx];
459 if (*offset > 0) {
460 /* same offset, no problem */
461 if (*offset == sym_offset)
462 continue;
463 /* handle multiple matches */
464 if (found->bind != STB_WEAK && bind != STB_WEAK) {
465 /* Only accept one non-weak bind. */
466 pr_warn("elf: ambiguous match found '%s@%lu' in '%s' previous offset %lu\n",
467 sym->name, sym_offset, binary_path, *offset);
468 err = -ESRCH;
469 goto out;
470 } else if (bind == STB_WEAK) {
471 /* already have a non-weak bind, and
472 * this is a weak bind, so ignore.
473 */
474 continue;
475 }
476 } else {
477 cnt_done++;
478 }
479 *offset = sym_offset;
480 found->bind = bind;
481 }
482 }
483
484 if (cnt != cnt_done) {
485 err = -ENOENT;
486 goto out;
487 }
488
489 *poffsets = offsets;
490
491out:
492 free(symbols);
493 if (err)
494 free(offsets);
495 elf_close(&elf_fd);
496 return err;
497}
498
499/*
500 * Return offsets in @poffsets for symbols specified by @pattern argument.
501 * On success returns 0 and offsets are returned in allocated @poffsets
502 * array with the @pctn size, that needs to be released by the caller.
503 */
504int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
505 unsigned long **poffsets, size_t *pcnt)
506{
507 int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM };
508 unsigned long *offsets = NULL;
509 size_t cap = 0, cnt = 0;
510 struct elf_fd elf_fd;
511 int err = 0, i;
512
513 err = elf_open(binary_path, &elf_fd);
514 if (err)
515 return err;
516
517 for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
518 struct elf_sym_iter iter;
519 struct elf_sym *sym;
520
521 err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
522 if (err == -ENOENT)
523 continue;
524 if (err)
525 goto out;
526
527 while ((sym = elf_sym_iter_next(&iter))) {
528 if (!glob_match(sym->name, pattern))
529 continue;
530
531 err = libbpf_ensure_mem((void **) &offsets, &cap, sizeof(*offsets),
532 cnt + 1);
533 if (err)
534 goto out;
535
536 offsets[cnt++] = elf_sym_offset(sym);
537 }
538
539 /* If we found anything in the first symbol section,
540 * do not search others to avoid duplicates.
541 */
542 if (cnt)
543 break;
544 }
545
546 if (cnt) {
547 *poffsets = offsets;
548 *pcnt = cnt;
549 } else {
550 err = -ENOENT;
551 }
552
553out:
554 if (err)
555 free(offsets);
556 elf_close(&elf_fd);
557 return err;
558}