1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Post mortem Dwarf CFI based unwinding on top of regs and stack dumps.
4  *
5  * Lots of this code have been borrowed or heavily inspired from parts of
6  * the libunwind 0.99 code which are (amongst other contributors I may have
7  * forgotten):
8  *
9  * Copyright (C) 2002-2007 Hewlett-Packard Co
10  *	Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
11  *
12  * And the bugs have been added by:
13  *
14  * Copyright (C) 2010, Frederic Weisbecker <fweisbec@gmail.com>
15  * Copyright (C) 2012, Jiri Olsa <jolsa@redhat.com>
16  *
17  */
18 
19 #include <elf.h>
20 #include <errno.h>
21 #include <gelf.h>
22 #include <fcntl.h>
23 #include <inttypes.h>
24 #include <string.h>
25 #include <unistd.h>
26 #include <sys/mman.h>
27 #include <linux/list.h>
28 #include <linux/zalloc.h>
29 #ifndef REMOTE_UNWIND_LIBUNWIND
30 #include <libunwind.h>
31 #include <libunwind-ptrace.h>
32 #endif
33 #include "callchain.h"
34 #include "thread.h"
35 #include "session.h"
36 #include "perf_regs.h"
37 #include "unwind.h"
38 #include "map.h"
39 #include "symbol.h"
40 #include "debug.h"
41 #include "asm/bug.h"
42 #include "dso.h"
43 
44 extern int
45 UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
46 				    unw_word_t ip,
47 				    unw_dyn_info_t *di,
48 				    unw_proc_info_t *pi,
49 				    int need_unwind_info, void *arg);
50 
51 #define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
52 
53 extern int
54 UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
55 				 unw_word_t ip,
56 				 unw_word_t segbase,
57 				 const char *obj_name, unw_word_t start,
58 				 unw_word_t end);
59 
60 #define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
61 
62 #define DW_EH_PE_FORMAT_MASK	0x0f	/* format of the encoded value */
63 #define DW_EH_PE_APPL_MASK	0x70	/* how the value is to be applied */
64 
65 /* Pointer-encoding formats: */
66 #define DW_EH_PE_omit		0xff
67 #define DW_EH_PE_ptr		0x00	/* pointer-sized unsigned value */
68 #define DW_EH_PE_udata4		0x03	/* unsigned 32-bit value */
69 #define DW_EH_PE_udata8		0x04	/* unsigned 64-bit value */
70 #define DW_EH_PE_sdata4		0x0b	/* signed 32-bit value */
71 #define DW_EH_PE_sdata8		0x0c	/* signed 64-bit value */
72 
73 /* Pointer-encoding application: */
74 #define DW_EH_PE_absptr		0x00	/* absolute value */
75 #define DW_EH_PE_pcrel		0x10	/* rel. to addr. of encoded value */
76 
77 /*
78  * The following are not documented by LSB v1.3, yet they are used by
79  * GCC, presumably they aren't documented by LSB since they aren't
80  * used on Linux:
81  */
82 #define DW_EH_PE_funcrel	0x40	/* start-of-procedure-relative */
83 #define DW_EH_PE_aligned	0x50	/* aligned pointer */
84 
85 /* Flags intentionally not handled, since they're not needed:
86  * #define DW_EH_PE_indirect      0x80
87  * #define DW_EH_PE_uleb128       0x01
88  * #define DW_EH_PE_udata2        0x02
89  * #define DW_EH_PE_sleb128       0x09
90  * #define DW_EH_PE_sdata2        0x0a
91  * #define DW_EH_PE_textrel       0x20
92  * #define DW_EH_PE_datarel       0x30
93  */
94 
95 struct unwind_info {
96 	struct perf_sample	*sample;
97 	struct machine		*machine;
98 	struct thread		*thread;
99 	bool			 best_effort;
100 };
101 
102 #define dw_read(ptr, type, end) ({	\
103 	type *__p = (type *) ptr;	\
104 	type  __v;			\
105 	if ((__p + 1) > (type *) end)	\
106 		return -EINVAL;		\
107 	__v = *__p++;			\
108 	ptr = (typeof(ptr)) __p;	\
109 	__v;				\
110 	})
111 
112 static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
113 				   u8 encoding)
114 {
115 	u8 *cur = *p;
116 	*val = 0;
117 
118 	switch (encoding) {
119 	case DW_EH_PE_omit:
120 		*val = 0;
121 		goto out;
122 	case DW_EH_PE_ptr:
123 		*val = dw_read(cur, unsigned long, end);
124 		goto out;
125 	default:
126 		break;
127 	}
128 
129 	switch (encoding & DW_EH_PE_APPL_MASK) {
130 	case DW_EH_PE_absptr:
131 		break;
132 	case DW_EH_PE_pcrel:
133 		*val = (unsigned long) cur;
134 		break;
135 	default:
136 		return -EINVAL;
137 	}
138 
139 	if ((encoding & 0x07) == 0x00)
140 		encoding |= DW_EH_PE_udata4;
141 
142 	switch (encoding & DW_EH_PE_FORMAT_MASK) {
143 	case DW_EH_PE_sdata4:
144 		*val += dw_read(cur, s32, end);
145 		break;
146 	case DW_EH_PE_udata4:
147 		*val += dw_read(cur, u32, end);
148 		break;
149 	case DW_EH_PE_sdata8:
150 		*val += dw_read(cur, s64, end);
151 		break;
152 	case DW_EH_PE_udata8:
153 		*val += dw_read(cur, u64, end);
154 		break;
155 	default:
156 		return -EINVAL;
157 	}
158 
159  out:
160 	*p = cur;
161 	return 0;
162 }
163 
164 #define dw_read_encoded_value(ptr, end, enc) ({			\
165 	u64 __v;						\
166 	if (__dw_read_encoded_value(&ptr, end, &__v, enc)) {	\
167 		return -EINVAL;                                 \
168 	}                                                       \
169 	__v;                                                    \
170 	})
171 
172 static u64 elf_section_offset(int fd, const char *name)
173 {
174 	Elf *elf;
175 	GElf_Ehdr ehdr;
176 	GElf_Shdr shdr;
177 	u64 offset = 0;
178 
179 	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
180 	if (elf == NULL)
181 		return 0;
182 
183 	do {
184 		if (gelf_getehdr(elf, &ehdr) == NULL)
185 			break;
186 
187 		if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
188 			break;
189 
190 		offset = shdr.sh_offset;
191 	} while (0);
192 
193 	elf_end(elf);
194 	return offset;
195 }
196 
197 #ifndef NO_LIBUNWIND_DEBUG_FRAME
198 static int elf_is_exec(int fd, const char *name)
199 {
200 	Elf *elf;
201 	GElf_Ehdr ehdr;
202 	int retval = 0;
203 
204 	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
205 	if (elf == NULL)
206 		return 0;
207 	if (gelf_getehdr(elf, &ehdr) == NULL)
208 		goto out;
209 
210 	retval = (ehdr.e_type == ET_EXEC);
211 
212 out:
213 	elf_end(elf);
214 	pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
215 	return retval;
216 }
217 #endif
218 
219 struct table_entry {
220 	u32 start_ip_offset;
221 	u32 fde_offset;
222 };
223 
224 struct eh_frame_hdr {
225 	unsigned char version;
226 	unsigned char eh_frame_ptr_enc;
227 	unsigned char fde_count_enc;
228 	unsigned char table_enc;
229 
230 	/*
231 	 * The rest of the header is variable-length and consists of the
232 	 * following members:
233 	 *
234 	 *	encoded_t eh_frame_ptr;
235 	 *	encoded_t fde_count;
236 	 */
237 
238 	/* A single encoded pointer should not be more than 8 bytes. */
239 	u64 enc[2];
240 
241 	/*
242 	 * struct {
243 	 *    encoded_t start_ip;
244 	 *    encoded_t fde_addr;
245 	 * } binary_search_table[fde_count];
246 	 */
247 	char data[];
248 } __packed;
249 
250 static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
251 			       u64 offset, u64 *table_data, u64 *segbase,
252 			       u64 *fde_count)
253 {
254 	struct eh_frame_hdr hdr;
255 	u8 *enc = (u8 *) &hdr.enc;
256 	u8 *end = (u8 *) &hdr.data;
257 	ssize_t r;
258 
259 	r = dso__data_read_offset(dso, machine, offset,
260 				  (u8 *) &hdr, sizeof(hdr));
261 	if (r != sizeof(hdr))
262 		return -EINVAL;
263 
264 	/* We dont need eh_frame_ptr, just skip it. */
265 	dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
266 
267 	*fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
268 	*segbase    = offset;
269 	*table_data = (enc - (u8 *) &hdr) + offset;
270 	return 0;
271 }
272 
273 static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
274 				     u64 *table_data, u64 *segbase,
275 				     u64 *fde_count)
276 {
277 	int ret = -EINVAL, fd;
278 	u64 offset = dso->data.eh_frame_hdr_offset;
279 
280 	if (offset == 0) {
281 		fd = dso__data_get_fd(dso, machine);
282 		if (fd < 0)
283 			return -EINVAL;
284 
285 		/* Check the .eh_frame section for unwinding info */
286 		offset = elf_section_offset(fd, ".eh_frame_hdr");
287 		dso->data.eh_frame_hdr_offset = offset;
288 		dso__data_put_fd(dso);
289 	}
290 
291 	if (offset)
292 		ret = unwind_spec_ehframe(dso, machine, offset,
293 					  table_data, segbase,
294 					  fde_count);
295 
296 	return ret;
297 }
298 
299 #ifndef NO_LIBUNWIND_DEBUG_FRAME
300 static int read_unwind_spec_debug_frame(struct dso *dso,
301 					struct machine *machine, u64 *offset)
302 {
303 	int fd;
304 	u64 ofs = dso->data.debug_frame_offset;
305 
306 	/* debug_frame can reside in:
307 	 *  - dso
308 	 *  - debug pointed by symsrc_filename
309 	 *  - gnu_debuglink, which doesn't necessary
310 	 *    has to be pointed by symsrc_filename
311 	 */
312 	if (ofs == 0) {
313 		fd = dso__data_get_fd(dso, machine);
314 		if (fd >= 0) {
315 			ofs = elf_section_offset(fd, ".debug_frame");
316 			dso__data_put_fd(dso);
317 		}
318 
319 		if (ofs <= 0) {
320 			fd = open(dso->symsrc_filename, O_RDONLY);
321 			if (fd >= 0) {
322 				ofs = elf_section_offset(fd, ".debug_frame");
323 				close(fd);
324 			}
325 		}
326 
327 		if (ofs <= 0) {
328 			char *debuglink = malloc(PATH_MAX);
329 			int ret = 0;
330 
331 			ret = dso__read_binary_type_filename(
332 				dso, DSO_BINARY_TYPE__DEBUGLINK,
333 				machine->root_dir, debuglink, PATH_MAX);
334 			if (!ret) {
335 				fd = open(debuglink, O_RDONLY);
336 				if (fd >= 0) {
337 					ofs = elf_section_offset(fd,
338 							".debug_frame");
339 					close(fd);
340 				}
341 			}
342 			if (ofs > 0) {
343 				if (dso->symsrc_filename != NULL) {
344 					pr_warning(
345 						"%s: overwrite symsrc(%s,%s)\n",
346 							__func__,
347 							dso->symsrc_filename,
348 							debuglink);
349 					zfree(&dso->symsrc_filename);
350 				}
351 				dso->symsrc_filename = debuglink;
352 			} else {
353 				free(debuglink);
354 			}
355 		}
356 
357 		dso->data.debug_frame_offset = ofs;
358 	}
359 
360 	*offset = ofs;
361 	if (*offset)
362 		return 0;
363 
364 	return -EINVAL;
365 }
366 #endif
367 
368 static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
369 {
370 	struct addr_location al;
371 	return thread__find_map(ui->thread, PERF_RECORD_MISC_USER, ip, &al);
372 }
373 
374 static int
375 find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
376 	       int need_unwind_info, void *arg)
377 {
378 	struct unwind_info *ui = arg;
379 	struct map *map;
380 	unw_dyn_info_t di;
381 	u64 table_data, segbase, fde_count;
382 	int ret = -EINVAL;
383 
384 	map = find_map(ip, ui);
385 	if (!map || !map->dso)
386 		return -EINVAL;
387 
388 	pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
389 
390 	/* Check the .eh_frame section for unwinding info */
391 	if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
392 				       &table_data, &segbase, &fde_count)) {
393 		memset(&di, 0, sizeof(di));
394 		di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
395 		di.start_ip = map->start;
396 		di.end_ip   = map->end;
397 		di.u.rti.segbase    = map->start + segbase - map->pgoff;
398 		di.u.rti.table_data = map->start + table_data - map->pgoff;
399 		di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
400 				      / sizeof(unw_word_t);
401 		ret = dwarf_search_unwind_table(as, ip, &di, pi,
402 						need_unwind_info, arg);
403 	}
404 
405 #ifndef NO_LIBUNWIND_DEBUG_FRAME
406 	/* Check the .debug_frame section for unwinding info */
407 	if (ret < 0 &&
408 	    !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
409 		int fd = dso__data_get_fd(map->dso, ui->machine);
410 		int is_exec = elf_is_exec(fd, map->dso->name);
411 		unw_word_t base = is_exec ? 0 : map->start;
412 		const char *symfile;
413 
414 		if (fd >= 0)
415 			dso__data_put_fd(map->dso);
416 
417 		symfile = map->dso->symsrc_filename ?: map->dso->name;
418 
419 		memset(&di, 0, sizeof(di));
420 		if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
421 					   map->start, map->end))
422 			return dwarf_search_unwind_table(as, ip, &di, pi,
423 							 need_unwind_info, arg);
424 	}
425 #endif
426 
427 	return ret;
428 }
429 
430 static int access_fpreg(unw_addr_space_t __maybe_unused as,
431 			unw_regnum_t __maybe_unused num,
432 			unw_fpreg_t __maybe_unused *val,
433 			int __maybe_unused __write,
434 			void __maybe_unused *arg)
435 {
436 	pr_err("unwind: access_fpreg unsupported\n");
437 	return -UNW_EINVAL;
438 }
439 
440 static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
441 				  unw_word_t __maybe_unused *dil_addr,
442 				  void __maybe_unused *arg)
443 {
444 	return -UNW_ENOINFO;
445 }
446 
447 static int resume(unw_addr_space_t __maybe_unused as,
448 		  unw_cursor_t __maybe_unused *cu,
449 		  void __maybe_unused *arg)
450 {
451 	pr_err("unwind: resume unsupported\n");
452 	return -UNW_EINVAL;
453 }
454 
455 static int
456 get_proc_name(unw_addr_space_t __maybe_unused as,
457 	      unw_word_t __maybe_unused addr,
458 		char __maybe_unused *bufp, size_t __maybe_unused buf_len,
459 		unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
460 {
461 	pr_err("unwind: get_proc_name unsupported\n");
462 	return -UNW_EINVAL;
463 }
464 
465 static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
466 			  unw_word_t *data)
467 {
468 	struct map *map;
469 	ssize_t size;
470 
471 	map = find_map(addr, ui);
472 	if (!map) {
473 		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
474 		return -1;
475 	}
476 
477 	if (!map->dso)
478 		return -1;
479 
480 	size = dso__data_read_addr(map->dso, map, ui->machine,
481 				   addr, (u8 *) data, sizeof(*data));
482 
483 	return !(size == sizeof(*data));
484 }
485 
486 static int access_mem(unw_addr_space_t __maybe_unused as,
487 		      unw_word_t addr, unw_word_t *valp,
488 		      int __write, void *arg)
489 {
490 	struct unwind_info *ui = arg;
491 	struct stack_dump *stack = &ui->sample->user_stack;
492 	u64 start, end;
493 	int offset;
494 	int ret;
495 
496 	/* Don't support write, probably not needed. */
497 	if (__write || !stack || !ui->sample->user_regs.regs) {
498 		*valp = 0;
499 		return 0;
500 	}
501 
502 	ret = perf_reg_value(&start, &ui->sample->user_regs,
503 			     LIBUNWIND__ARCH_REG_SP);
504 	if (ret)
505 		return ret;
506 
507 	end = start + stack->size;
508 
509 	/* Check overflow. */
510 	if (addr + sizeof(unw_word_t) < addr)
511 		return -EINVAL;
512 
513 	if (addr < start || addr + sizeof(unw_word_t) >= end) {
514 		ret = access_dso_mem(ui, addr, valp);
515 		if (ret) {
516 			pr_debug("unwind: access_mem %p not inside range"
517 				 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
518 				 (void *) (uintptr_t) addr, start, end);
519 			*valp = 0;
520 			return ret;
521 		}
522 		return 0;
523 	}
524 
525 	offset = addr - start;
526 	*valp  = *(unw_word_t *)&stack->data[offset];
527 	pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
528 		 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
529 	return 0;
530 }
531 
532 static int access_reg(unw_addr_space_t __maybe_unused as,
533 		      unw_regnum_t regnum, unw_word_t *valp,
534 		      int __write, void *arg)
535 {
536 	struct unwind_info *ui = arg;
537 	int id, ret;
538 	u64 val;
539 
540 	/* Don't support write, I suspect we don't need it. */
541 	if (__write) {
542 		pr_err("unwind: access_reg w %d\n", regnum);
543 		return 0;
544 	}
545 
546 	if (!ui->sample->user_regs.regs) {
547 		*valp = 0;
548 		return 0;
549 	}
550 
551 	id = LIBUNWIND__ARCH_REG_ID(regnum);
552 	if (id < 0)
553 		return -EINVAL;
554 
555 	ret = perf_reg_value(&val, &ui->sample->user_regs, id);
556 	if (ret) {
557 		if (!ui->best_effort)
558 			pr_err("unwind: can't read reg %d\n", regnum);
559 		return ret;
560 	}
561 
562 	*valp = (unw_word_t) val;
563 	pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
564 	return 0;
565 }
566 
567 static void put_unwind_info(unw_addr_space_t __maybe_unused as,
568 			    unw_proc_info_t *pi __maybe_unused,
569 			    void *arg __maybe_unused)
570 {
571 	pr_debug("unwind: put_unwind_info called\n");
572 }
573 
574 static int entry(u64 ip, struct thread *thread,
575 		 unwind_entry_cb_t cb, void *arg)
576 {
577 	struct unwind_entry e;
578 	struct addr_location al;
579 
580 	e.ms.sym = thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
581 	e.ip     = ip;
582 	e.ms.map = al.map;
583 	e.ms.maps = al.maps;
584 
585 	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
586 		 al.sym ? al.sym->name : "''",
587 		 ip,
588 		 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
589 
590 	return cb(&e, arg);
591 }
592 
593 static void display_error(int err)
594 {
595 	switch (err) {
596 	case UNW_EINVAL:
597 		pr_err("unwind: Only supports local.\n");
598 		break;
599 	case UNW_EUNSPEC:
600 		pr_err("unwind: Unspecified error.\n");
601 		break;
602 	case UNW_EBADREG:
603 		pr_err("unwind: Register unavailable.\n");
604 		break;
605 	default:
606 		break;
607 	}
608 }
609 
610 static unw_accessors_t accessors = {
611 	.find_proc_info		= find_proc_info,
612 	.put_unwind_info	= put_unwind_info,
613 	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
614 	.access_mem		= access_mem,
615 	.access_reg		= access_reg,
616 	.access_fpreg		= access_fpreg,
617 	.resume			= resume,
618 	.get_proc_name		= get_proc_name,
619 };
620 
621 static int _unwind__prepare_access(struct maps *maps)
622 {
623 	maps->addr_space = unw_create_addr_space(&accessors, 0);
624 	if (!maps->addr_space) {
625 		pr_err("unwind: Can't create unwind address space.\n");
626 		return -ENOMEM;
627 	}
628 
629 	unw_set_caching_policy(maps->addr_space, UNW_CACHE_GLOBAL);
630 	return 0;
631 }
632 
633 static void _unwind__flush_access(struct maps *maps)
634 {
635 	unw_flush_cache(maps->addr_space, 0, 0);
636 }
637 
638 static void _unwind__finish_access(struct maps *maps)
639 {
640 	unw_destroy_addr_space(maps->addr_space);
641 }
642 
643 static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
644 		       void *arg, int max_stack)
645 {
646 	u64 val;
647 	unw_word_t ips[max_stack];
648 	unw_addr_space_t addr_space;
649 	unw_cursor_t c;
650 	int ret, i = 0;
651 
652 	ret = perf_reg_value(&val, &ui->sample->user_regs,
653 			     LIBUNWIND__ARCH_REG_IP);
654 	if (ret)
655 		return ret;
656 
657 	ips[i++] = (unw_word_t) val;
658 
659 	/*
660 	 * If we need more than one entry, do the DWARF
661 	 * unwind itself.
662 	 */
663 	if (max_stack - 1 > 0) {
664 		WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
665 		addr_space = ui->thread->maps->addr_space;
666 
667 		if (addr_space == NULL)
668 			return -1;
669 
670 		ret = unw_init_remote(&c, addr_space, ui);
671 		if (ret && !ui->best_effort)
672 			display_error(ret);
673 
674 		while (!ret && (unw_step(&c) > 0) && i < max_stack) {
675 			unw_get_reg(&c, UNW_REG_IP, &ips[i]);
676 
677 			/*
678 			 * Decrement the IP for any non-activation frames.
679 			 * this is required to properly find the srcline
680 			 * for caller frames.
681 			 * See also the documentation for dwfl_frame_pc(),
682 			 * which this code tries to replicate.
683 			 */
684 			if (unw_is_signal_frame(&c) <= 0)
685 				--ips[i];
686 
687 			++i;
688 		}
689 
690 		max_stack = i;
691 	}
692 
693 	/*
694 	 * Display what we got based on the order setup.
695 	 */
696 	for (i = 0; i < max_stack && !ret; i++) {
697 		int j = i;
698 
699 		if (callchain_param.order == ORDER_CALLER)
700 			j = max_stack - i - 1;
701 		ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
702 	}
703 
704 	return ret;
705 }
706 
707 static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
708 			struct thread *thread,
709 			struct perf_sample *data, int max_stack,
710 			bool best_effort)
711 {
712 	struct unwind_info ui = {
713 		.sample       = data,
714 		.thread       = thread,
715 		.machine      = thread->maps->machine,
716 		.best_effort  = best_effort
717 	};
718 
719 	if (!data->user_regs.regs)
720 		return -EINVAL;
721 
722 	if (max_stack <= 0)
723 		return -EINVAL;
724 
725 	return get_entries(&ui, cb, arg, max_stack);
726 }
727 
728 static struct unwind_libunwind_ops
729 _unwind_libunwind_ops = {
730 	.prepare_access = _unwind__prepare_access,
731 	.flush_access   = _unwind__flush_access,
732 	.finish_access  = _unwind__finish_access,
733 	.get_entries    = _unwind__get_entries,
734 };
735 
736 #ifndef REMOTE_UNWIND_LIBUNWIND
737 struct unwind_libunwind_ops *
738 local_unwind_libunwind_ops = &_unwind_libunwind_ops;
739 #endif
740