summaryrefslogtreecommitdiffstats
path: root/tools/lib/bpf/elf.c
blob: 9d0296c1726a8e616622961e134650aea47c73d5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
#include <linux/kernel.h>

#include "libbpf_internal.h"
#include "str_error.h"

#define STRERR_BUFSIZE  128

int elf_open(const char *binary_path, struct elf_fd *elf_fd)
{
	char errmsg[STRERR_BUFSIZE];
	int fd, ret;
	Elf *elf;

	if (elf_version(EV_CURRENT) == EV_NONE) {
		pr_warn("elf: failed to init libelf for %s\n", binary_path);
		return -LIBBPF_ERRNO__LIBELF;
	}
	fd = open(binary_path, O_RDONLY | O_CLOEXEC);
	if (fd < 0) {
		ret = -errno;
		pr_warn("elf: failed to open %s: %s\n", binary_path,
			libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
		return ret;
	}
	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
	if (!elf) {
		pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
		close(fd);
		return -LIBBPF_ERRNO__FORMAT;
	}
	elf_fd->fd = fd;
	elf_fd->elf = elf;
	return 0;
}

void elf_close(struct elf_fd *elf_fd)
{
	if (!elf_fd)
		return;
	elf_end(elf_fd->elf);
	close(elf_fd->fd);
}

/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
{
	while ((scn = elf_nextscn(elf, scn)) != NULL) {
		GElf_Shdr sh;

		if (!gelf_getshdr(scn, &sh))
			continue;
		if (sh.sh_type == sh_type)
			return scn;
	}
	return NULL;
}

struct elf_sym {
	const char *name;
	GElf_Sym sym;
	GElf_Shdr sh;
};

struct elf_sym_iter {
	Elf *elf;
	Elf_Data *syms;
	size_t nr_syms;
	size_t strtabidx;
	size_t next_sym_idx;
	struct elf_sym sym;
	int st_type;
};

static int elf_sym_iter_new(struct elf_sym_iter *iter,
			    Elf *elf, const char *binary_path,
			    int sh_type, int st_type)
{
	Elf_Scn *scn = NULL;
	GElf_Ehdr ehdr;
	GElf_Shdr sh;

	memset(iter, 0, sizeof(*iter));

	if (!gelf_getehdr(elf, &ehdr)) {
		pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
		return -EINVAL;
	}

	scn = elf_find_next_scn_by_type(elf, sh_type, NULL);
	if (!scn) {
		pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
			 binary_path);
		return -ENOENT;
	}

	if (!gelf_getshdr(scn, &sh))
		return -EINVAL;

	iter->strtabidx = sh.sh_link;
	iter->syms = elf_getdata(scn, 0);
	if (!iter->syms) {
		pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
			binary_path, elf_errmsg(-1));
		return -EINVAL;
	}
	iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
	iter->elf = elf;
	iter->st_type = st_type;
	return 0;
}

static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
{
	struct elf_sym *ret = &iter->sym;
	GElf_Sym *sym = &ret->sym;
	const char *name = NULL;
	Elf_Scn *sym_scn;
	size_t idx;

	for (idx = iter->next_sym_idx; idx < iter->nr_syms; idx++) {
		if (!gelf_getsym(iter->syms, idx, sym))
			continue;
		if (GELF_ST_TYPE(sym->st_info) != iter->st_type)
			continue;
		name = elf_strptr(iter->elf, iter->strtabidx, sym->st_name);
		if (!name)
			continue;
		sym_scn = elf_getscn(iter->elf, sym->st_shndx);
		if (!sym_scn)
			continue;
		if (!gelf_getshdr(sym_scn, &ret->sh))
			continue;

		iter->next_sym_idx = idx + 1;
		ret->name = name;
		return ret;
	}

	return NULL;
}


/* Transform symbol's virtual address (absolute for binaries and relative
 * for shared libs) into file offset, which is what kernel is expecting
 * for uprobe/uretprobe attachment.
 * See Documentation/trace/uprobetracer.rst for more details. This is done
 * by looking up symbol's containing section's header and using iter's virtual
 * address (sh_addr) and corresponding file offset (sh_offset) to transform
 * sym.st_value (virtual address) into desired final file offset.
 */
static unsigned long elf_sym_offset(struct elf_sym *sym)
{
	return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
}

/* Find offset of function name in the provided ELF object. "binary_path" is
 * the path to the ELF binary represented by "elf", and only used for error
 * reporting matters. "name" matches symbol name or name@@LIB for library
 * functions.
 */
long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
{
	int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
	bool is_shared_lib, is_name_qualified;
	long ret = -ENOENT;
	size_t name_len;
	GElf_Ehdr ehdr;

	if (!gelf_getehdr(elf, &ehdr)) {
		pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
		ret = -LIBBPF_ERRNO__FORMAT;
		goto out;
	}
	/* for shared lib case, we do not need to calculate relative offset */
	is_shared_lib = ehdr.e_type == ET_DYN;

	name_len = strlen(name);
	/* Does name specify "@@LIB"? */
	is_name_qualified = strstr(name, "@@") != NULL;

	/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
	 * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
	 * linked binary may not have SHT_DYMSYM, so absence of a section should not be
	 * reported as a warning/error.
	 */
	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
		struct elf_sym_iter iter;
		struct elf_sym *sym;
		int last_bind = -1;
		int cur_bind;

		ret = elf_sym_iter_new(&iter, elf, binary_path, sh_types[i], STT_FUNC);
		if (ret == -ENOENT)
			continue;
		if (ret)
			goto out;

		while ((sym = elf_sym_iter_next(&iter))) {
			/* User can specify func, func@@LIB or func@@LIB_VERSION. */
			if (strncmp(sym->name, name, name_len) != 0)
				continue;
			/* ...but we don't want a search for "foo" to match 'foo2" also, so any
			 * additional characters in sname should be of the form "@@LIB".
			 */
			if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
				continue;

			cur_bind = GELF_ST_BIND(sym->sym.st_info);

			if (ret > 0) {
				/* handle multiple matches */
				if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
					/* Only accept one non-weak bind. */
					pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
						sym->name, name, binary_path);
					ret = -LIBBPF_ERRNO__FORMAT;
					goto out;
				} else if (cur_bind == STB_WEAK) {
					/* already have a non-weak bind, and
					 * this is a weak bind, so ignore.
					 */
					continue;
				}
			}

			ret = elf_sym_offset(sym);
			last_bind = cur_bind;
		}
		if (ret > 0)
			break;
	}

	if (ret > 0) {
		pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
			 ret);
	} else {
		if (ret == 0) {
			pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
				is_shared_lib ? "should not be 0 in a shared library" :
						"try using shared library path instead");
			ret = -ENOENT;
		} else {
			pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
		}
	}
out:
	return ret;
}

/* Find offset of function name in ELF object specified by path. "name" matches
 * symbol name or name@@LIB for library functions.
 */
long elf_find_func_offset_from_file(const char *binary_path, const char *name)
{
	struct elf_fd elf_fd;
	long ret = -ENOENT;

	ret = elf_open(binary_path, &elf_fd);
	if (ret)
		return ret;
	ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
	elf_close(&elf_fd);
	return ret;
}

struct symbol {
	const char *name;
	int bind;
	int idx;
};

static int symbol_cmp(const void *a, const void *b)
{
	const struct symbol *sym_a = a;
	const struct symbol *sym_b = b;

	return strcmp(sym_a->name, sym_b->name);
}

/*
 * Return offsets in @poffsets for symbols specified in @syms array argument.
 * On success returns 0 and offsets are returned in allocated array with @cnt
 * size, that needs to be released by the caller.
 */
int elf_resolve_syms_offsets(const char *binary_path, int cnt,
			     const char **syms, unsigned long **poffsets)
{
	int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
	int err = 0, i, cnt_done = 0;
	unsigned long *offsets;
	struct symbol *symbols;
	struct elf_fd elf_fd;

	err = elf_open(binary_path, &elf_fd);
	if (err)
		return err;

	offsets = calloc(cnt, sizeof(*offsets));
	symbols = calloc(cnt, sizeof(*symbols));

	if (!offsets || !symbols) {
		err = -ENOMEM;
		goto out;
	}

	for (i = 0; i < cnt; i++) {
		symbols[i].name = syms[i];
		symbols[i].idx = i;
	}

	qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);

	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
		struct elf_sym_iter iter;
		struct elf_sym *sym;

		err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
		if (err == -ENOENT)
			continue;
		if (err)
			goto out;

		while ((sym = elf_sym_iter_next(&iter))) {
			unsigned long sym_offset = elf_sym_offset(sym);
			int bind = GELF_ST_BIND(sym->sym.st_info);
			struct symbol *found, tmp = {
				.name = sym->name,
			};
			unsigned long *offset;

			found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
			if (!found)
				continue;

			offset = &offsets[found->idx];
			if (*offset > 0) {
				/* same offset, no problem */
				if (*offset == sym_offset)
					continue;
				/* handle multiple matches */
				if (found->bind != STB_WEAK && bind != STB_WEAK) {
					/* Only accept one non-weak bind. */
					pr_warn("elf: ambiguous match found '%s@%lu' in '%s' previous offset %lu\n",
						sym->name, sym_offset, binary_path, *offset);
					err = -ESRCH;
					goto out;
				} else if (bind == STB_WEAK) {
					/* already have a non-weak bind, and
					 * this is a weak bind, so ignore.
					 */
					continue;
				}
			} else {
				cnt_done++;
			}
			*offset = sym_offset;
			found->bind = bind;
		}
	}

	if (cnt != cnt_done) {
		err = -ENOENT;
		goto out;
	}

	*poffsets = offsets;

out:
	free(symbols);
	if (err)
		free(offsets);
	elf_close(&elf_fd);
	return err;
}

/*
 * Return offsets in @poffsets for symbols specified by @pattern argument.
 * On success returns 0 and offsets are returned in allocated @poffsets
 * array with the @pctn size, that needs to be released by the caller.
 */
int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
				unsigned long **poffsets, size_t *pcnt)
{
	int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM };
	unsigned long *offsets = NULL;
	size_t cap = 0, cnt = 0;
	struct elf_fd elf_fd;
	int err = 0, i;

	err = elf_open(binary_path, &elf_fd);
	if (err)
		return err;

	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
		struct elf_sym_iter iter;
		struct elf_sym *sym;

		err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
		if (err == -ENOENT)
			continue;
		if (err)
			goto out;

		while ((sym = elf_sym_iter_next(&iter))) {
			if (!glob_match(sym->name, pattern))
				continue;

			err = libbpf_ensure_mem((void **) &offsets, &cap, sizeof(*offsets),
						cnt + 1);
			if (err)
				goto out;

			offsets[cnt++] = elf_sym_offset(sym);
		}

		/* If we found anything in the first symbol section,
		 * do not search others to avoid duplicates.
		 */
		if (cnt)
			break;
	}

	if (cnt) {
		*poffsets = offsets;
		*pcnt = cnt;
	} else {
		err = -ENOENT;
	}

out:
	if (err)
		free(offsets);
	elf_close(&elf_fd);
	return err;
}