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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
44extern int
45UNW_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
53extern int
54UNW_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
95struct 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
112static 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
172static int elf_section_address_and_offset(int fd, const char *name, u64 *address, u64 *offset)
173{
174 Elf *elf;
175 GElf_Ehdr ehdr;
176 GElf_Shdr shdr;
177 int ret = -1;
178
179 elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
180 if (elf == NULL)
181 return -1;
182
183 if (gelf_getehdr(elf, &ehdr) == NULL)
184 goto out_err;
185
186 if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
187 goto out_err;
188
189 *address = shdr.sh_addr;
190 *offset = shdr.sh_offset;
191 ret = 0;
192out_err:
193 elf_end(elf);
194 return ret;
195}
196
197#ifndef NO_LIBUNWIND_DEBUG_FRAME
198static u64 elf_section_offset(int fd, const char *name)
199{
200 u64 address, offset = 0;
201
202 if (elf_section_address_and_offset(fd, name, &address, &offset))
203 return 0;
204
205 return offset;
206}
207#endif
208
209static u64 elf_base_address(int fd)
210{
211 Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
212 GElf_Phdr phdr;
213 u64 retval = 0;
214 size_t i, phdrnum = 0;
215
216 if (elf == NULL)
217 return 0;
218 (void)elf_getphdrnum(elf, &phdrnum);
219 /* PT_LOAD segments are sorted by p_vaddr, so the first has the minimum p_vaddr. */
220 for (i = 0; i < phdrnum; i++) {
221 if (gelf_getphdr(elf, i, &phdr) && phdr.p_type == PT_LOAD) {
222 retval = phdr.p_vaddr & -getpagesize();
223 break;
224 }
225 }
226
227 elf_end(elf);
228 return retval;
229}
230
231#ifndef NO_LIBUNWIND_DEBUG_FRAME
232static int elf_is_exec(int fd, const char *name)
233{
234 Elf *elf;
235 GElf_Ehdr ehdr;
236 int retval = 0;
237
238 elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
239 if (elf == NULL)
240 return 0;
241 if (gelf_getehdr(elf, &ehdr) == NULL)
242 goto out;
243
244 retval = (ehdr.e_type == ET_EXEC);
245
246out:
247 elf_end(elf);
248 pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
249 return retval;
250}
251#endif
252
253struct table_entry {
254 u32 start_ip_offset;
255 u32 fde_offset;
256};
257
258struct eh_frame_hdr {
259 unsigned char version;
260 unsigned char eh_frame_ptr_enc;
261 unsigned char fde_count_enc;
262 unsigned char table_enc;
263
264 /*
265 * The rest of the header is variable-length and consists of the
266 * following members:
267 *
268 * encoded_t eh_frame_ptr;
269 * encoded_t fde_count;
270 */
271
272 /* A single encoded pointer should not be more than 8 bytes. */
273 u64 enc[2];
274
275 /*
276 * struct {
277 * encoded_t start_ip;
278 * encoded_t fde_addr;
279 * } binary_search_table[fde_count];
280 */
281 char data[];
282} __packed;
283
284static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
285 u64 offset, u64 *table_data_offset, u64 *fde_count)
286{
287 struct eh_frame_hdr hdr;
288 u8 *enc = (u8 *) &hdr.enc;
289 u8 *end = (u8 *) &hdr.data;
290 ssize_t r;
291
292 r = dso__data_read_offset(dso, machine, offset,
293 (u8 *) &hdr, sizeof(hdr));
294 if (r != sizeof(hdr))
295 return -EINVAL;
296
297 /* We dont need eh_frame_ptr, just skip it. */
298 dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
299
300 *fde_count = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
301 *table_data_offset = enc - (u8 *) &hdr;
302 return 0;
303}
304
305static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,
306 u64 *table_data, u64 *segbase,
307 u64 *fde_count)
308{
309 struct map *map;
310 u64 base_addr = UINT64_MAX;
311 int ret, fd;
312
313 if (dso->data.eh_frame_hdr_offset == 0) {
314 fd = dso__data_get_fd(dso, ui->machine);
315 if (fd < 0)
316 return -EINVAL;
317
318 /* Check the .eh_frame section for unwinding info */
319 ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",
320 &dso->data.eh_frame_hdr_addr,
321 &dso->data.eh_frame_hdr_offset);
322 dso->data.elf_base_addr = elf_base_address(fd);
323 dso__data_put_fd(dso);
324 if (ret || dso->data.eh_frame_hdr_offset == 0)
325 return -EINVAL;
326 }
327
328 maps__for_each_entry(ui->thread->maps, map) {
329 if (map->dso == dso && map->start < base_addr)
330 base_addr = map->start;
331 }
332 base_addr -= dso->data.elf_base_addr;
333 /* Address of .eh_frame_hdr */
334 *segbase = base_addr + dso->data.eh_frame_hdr_addr;
335 ret = unwind_spec_ehframe(dso, ui->machine, dso->data.eh_frame_hdr_offset,
336 table_data, fde_count);
337 if (ret)
338 return ret;
339 /* binary_search_table offset plus .eh_frame_hdr address */
340 *table_data += *segbase;
341 return 0;
342}
343
344#ifndef NO_LIBUNWIND_DEBUG_FRAME
345static int read_unwind_spec_debug_frame(struct dso *dso,
346 struct machine *machine, u64 *offset)
347{
348 int fd;
349 u64 ofs = dso->data.debug_frame_offset;
350
351 /* debug_frame can reside in:
352 * - dso
353 * - debug pointed by symsrc_filename
354 * - gnu_debuglink, which doesn't necessary
355 * has to be pointed by symsrc_filename
356 */
357 if (ofs == 0) {
358 fd = dso__data_get_fd(dso, machine);
359 if (fd >= 0) {
360 ofs = elf_section_offset(fd, ".debug_frame");
361 dso__data_put_fd(dso);
362 }
363
364 if (ofs <= 0) {
365 fd = open(dso->symsrc_filename, O_RDONLY);
366 if (fd >= 0) {
367 ofs = elf_section_offset(fd, ".debug_frame");
368 close(fd);
369 }
370 }
371
372 if (ofs <= 0) {
373 char *debuglink = malloc(PATH_MAX);
374 int ret = 0;
375
376 ret = dso__read_binary_type_filename(
377 dso, DSO_BINARY_TYPE__DEBUGLINK,
378 machine->root_dir, debuglink, PATH_MAX);
379 if (!ret) {
380 fd = open(debuglink, O_RDONLY);
381 if (fd >= 0) {
382 ofs = elf_section_offset(fd,
383 ".debug_frame");
384 close(fd);
385 }
386 }
387 if (ofs > 0) {
388 if (dso->symsrc_filename != NULL) {
389 pr_warning(
390 "%s: overwrite symsrc(%s,%s)\n",
391 __func__,
392 dso->symsrc_filename,
393 debuglink);
394 zfree(&dso->symsrc_filename);
395 }
396 dso->symsrc_filename = debuglink;
397 } else {
398 free(debuglink);
399 }
400 }
401
402 dso->data.debug_frame_offset = ofs;
403 }
404
405 *offset = ofs;
406 if (*offset)
407 return 0;
408
409 return -EINVAL;
410}
411#endif
412
413static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
414{
415 struct addr_location al;
416 return thread__find_map(ui->thread, PERF_RECORD_MISC_USER, ip, &al);
417}
418
419static int
420find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
421 int need_unwind_info, void *arg)
422{
423 struct unwind_info *ui = arg;
424 struct map *map;
425 unw_dyn_info_t di;
426 u64 table_data, segbase, fde_count;
427 int ret = -EINVAL;
428
429 map = find_map(ip, ui);
430 if (!map || !map->dso)
431 return -EINVAL;
432
433 pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
434
435 /* Check the .eh_frame section for unwinding info */
436 if (!read_unwind_spec_eh_frame(map->dso, ui,
437 &table_data, &segbase, &fde_count)) {
438 memset(&di, 0, sizeof(di));
439 di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
440 di.start_ip = map->start;
441 di.end_ip = map->end;
442 di.u.rti.segbase = segbase;
443 di.u.rti.table_data = table_data;
444 di.u.rti.table_len = fde_count * sizeof(struct table_entry)
445 / sizeof(unw_word_t);
446 ret = dwarf_search_unwind_table(as, ip, &di, pi,
447 need_unwind_info, arg);
448 }
449
450#ifndef NO_LIBUNWIND_DEBUG_FRAME
451 /* Check the .debug_frame section for unwinding info */
452 if (ret < 0 &&
453 !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
454 int fd = dso__data_get_fd(map->dso, ui->machine);
455 int is_exec = elf_is_exec(fd, map->dso->name);
456 unw_word_t base = is_exec ? 0 : map->start;
457 const char *symfile;
458
459 if (fd >= 0)
460 dso__data_put_fd(map->dso);
461
462 symfile = map->dso->symsrc_filename ?: map->dso->name;
463
464 memset(&di, 0, sizeof(di));
465 if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
466 map->start, map->end))
467 return dwarf_search_unwind_table(as, ip, &di, pi,
468 need_unwind_info, arg);
469 }
470#endif
471
472 return ret;
473}
474
475static int access_fpreg(unw_addr_space_t __maybe_unused as,
476 unw_regnum_t __maybe_unused num,
477 unw_fpreg_t __maybe_unused *val,
478 int __maybe_unused __write,
479 void __maybe_unused *arg)
480{
481 pr_err("unwind: access_fpreg unsupported\n");
482 return -UNW_EINVAL;
483}
484
485static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
486 unw_word_t __maybe_unused *dil_addr,
487 void __maybe_unused *arg)
488{
489 return -UNW_ENOINFO;
490}
491
492static int resume(unw_addr_space_t __maybe_unused as,
493 unw_cursor_t __maybe_unused *cu,
494 void __maybe_unused *arg)
495{
496 pr_err("unwind: resume unsupported\n");
497 return -UNW_EINVAL;
498}
499
500static int
501get_proc_name(unw_addr_space_t __maybe_unused as,
502 unw_word_t __maybe_unused addr,
503 char __maybe_unused *bufp, size_t __maybe_unused buf_len,
504 unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
505{
506 pr_err("unwind: get_proc_name unsupported\n");
507 return -UNW_EINVAL;
508}
509
510static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
511 unw_word_t *data)
512{
513 struct map *map;
514 ssize_t size;
515
516 map = find_map(addr, ui);
517 if (!map) {
518 pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
519 return -1;
520 }
521
522 if (!map->dso)
523 return -1;
524
525 size = dso__data_read_addr(map->dso, map, ui->machine,
526 addr, (u8 *) data, sizeof(*data));
527
528 return !(size == sizeof(*data));
529}
530
531static int access_mem(unw_addr_space_t __maybe_unused as,
532 unw_word_t addr, unw_word_t *valp,
533 int __write, void *arg)
534{
535 struct unwind_info *ui = arg;
536 struct stack_dump *stack = &ui->sample->user_stack;
537 u64 start, end;
538 int offset;
539 int ret;
540
541 /* Don't support write, probably not needed. */
542 if (__write || !stack || !ui->sample->user_regs.regs) {
543 *valp = 0;
544 return 0;
545 }
546
547 ret = perf_reg_value(&start, &ui->sample->user_regs,
548 LIBUNWIND__ARCH_REG_SP);
549 if (ret)
550 return ret;
551
552 end = start + stack->size;
553
554 /* Check overflow. */
555 if (addr + sizeof(unw_word_t) < addr)
556 return -EINVAL;
557
558 if (addr < start || addr + sizeof(unw_word_t) >= end) {
559 ret = access_dso_mem(ui, addr, valp);
560 if (ret) {
561 pr_debug("unwind: access_mem %p not inside range"
562 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
563 (void *) (uintptr_t) addr, start, end);
564 *valp = 0;
565 return ret;
566 }
567 return 0;
568 }
569
570 offset = addr - start;
571 *valp = *(unw_word_t *)&stack->data[offset];
572 pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
573 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
574 return 0;
575}
576
577static int access_reg(unw_addr_space_t __maybe_unused as,
578 unw_regnum_t regnum, unw_word_t *valp,
579 int __write, void *arg)
580{
581 struct unwind_info *ui = arg;
582 int id, ret;
583 u64 val;
584
585 /* Don't support write, I suspect we don't need it. */
586 if (__write) {
587 pr_err("unwind: access_reg w %d\n", regnum);
588 return 0;
589 }
590
591 if (!ui->sample->user_regs.regs) {
592 *valp = 0;
593 return 0;
594 }
595
596 id = LIBUNWIND__ARCH_REG_ID(regnum);
597 if (id < 0)
598 return -EINVAL;
599
600 ret = perf_reg_value(&val, &ui->sample->user_regs, id);
601 if (ret) {
602 if (!ui->best_effort)
603 pr_err("unwind: can't read reg %d\n", regnum);
604 return ret;
605 }
606
607 *valp = (unw_word_t) val;
608 pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
609 return 0;
610}
611
612static void put_unwind_info(unw_addr_space_t __maybe_unused as,
613 unw_proc_info_t *pi __maybe_unused,
614 void *arg __maybe_unused)
615{
616 pr_debug("unwind: put_unwind_info called\n");
617}
618
619static int entry(u64 ip, struct thread *thread,
620 unwind_entry_cb_t cb, void *arg)
621{
622 struct unwind_entry e;
623 struct addr_location al;
624
625 e.ms.sym = thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
626 e.ip = ip;
627 e.ms.map = al.map;
628 e.ms.maps = al.maps;
629
630 pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
631 al.sym ? al.sym->name : "''",
632 ip,
633 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
634
635 return cb(&e, arg);
636}
637
638static void display_error(int err)
639{
640 switch (err) {
641 case UNW_EINVAL:
642 pr_err("unwind: Only supports local.\n");
643 break;
644 case UNW_EUNSPEC:
645 pr_err("unwind: Unspecified error.\n");
646 break;
647 case UNW_EBADREG:
648 pr_err("unwind: Register unavailable.\n");
649 break;
650 default:
651 break;
652 }
653}
654
655static unw_accessors_t accessors = {
656 .find_proc_info = find_proc_info,
657 .put_unwind_info = put_unwind_info,
658 .get_dyn_info_list_addr = get_dyn_info_list_addr,
659 .access_mem = access_mem,
660 .access_reg = access_reg,
661 .access_fpreg = access_fpreg,
662 .resume = resume,
663 .get_proc_name = get_proc_name,
664};
665
666static int _unwind__prepare_access(struct maps *maps)
667{
668 maps->addr_space = unw_create_addr_space(&accessors, 0);
669 if (!maps->addr_space) {
670 pr_err("unwind: Can't create unwind address space.\n");
671 return -ENOMEM;
672 }
673
674 unw_set_caching_policy(maps->addr_space, UNW_CACHE_GLOBAL);
675 return 0;
676}
677
678static void _unwind__flush_access(struct maps *maps)
679{
680 unw_flush_cache(maps->addr_space, 0, 0);
681}
682
683static void _unwind__finish_access(struct maps *maps)
684{
685 unw_destroy_addr_space(maps->addr_space);
686}
687
688static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
689 void *arg, int max_stack)
690{
691 u64 val;
692 unw_word_t ips[max_stack];
693 unw_addr_space_t addr_space;
694 unw_cursor_t c;
695 int ret, i = 0;
696
697 ret = perf_reg_value(&val, &ui->sample->user_regs,
698 LIBUNWIND__ARCH_REG_IP);
699 if (ret)
700 return ret;
701
702 ips[i++] = (unw_word_t) val;
703
704 /*
705 * If we need more than one entry, do the DWARF
706 * unwind itself.
707 */
708 if (max_stack - 1 > 0) {
709 WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
710 addr_space = ui->thread->maps->addr_space;
711
712 if (addr_space == NULL)
713 return -1;
714
715 ret = unw_init_remote(&c, addr_space, ui);
716 if (ret && !ui->best_effort)
717 display_error(ret);
718
719 while (!ret && (unw_step(&c) > 0) && i < max_stack) {
720 unw_get_reg(&c, UNW_REG_IP, &ips[i]);
721
722 /*
723 * Decrement the IP for any non-activation frames.
724 * this is required to properly find the srcline
725 * for caller frames.
726 * See also the documentation for dwfl_frame_pc(),
727 * which this code tries to replicate.
728 */
729 if (unw_is_signal_frame(&c) <= 0)
730 --ips[i];
731
732 ++i;
733 }
734
735 max_stack = i;
736 }
737
738 /*
739 * Display what we got based on the order setup.
740 */
741 for (i = 0; i < max_stack && !ret; i++) {
742 int j = i;
743
744 if (callchain_param.order == ORDER_CALLER)
745 j = max_stack - i - 1;
746 ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
747 }
748
749 return ret;
750}
751
752static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
753 struct thread *thread,
754 struct perf_sample *data, int max_stack,
755 bool best_effort)
756{
757 struct unwind_info ui = {
758 .sample = data,
759 .thread = thread,
760 .machine = thread->maps->machine,
761 .best_effort = best_effort
762 };
763
764 if (!data->user_regs.regs)
765 return -EINVAL;
766
767 if (max_stack <= 0)
768 return -EINVAL;
769
770 return get_entries(&ui, cb, arg, max_stack);
771}
772
773static struct unwind_libunwind_ops
774_unwind_libunwind_ops = {
775 .prepare_access = _unwind__prepare_access,
776 .flush_access = _unwind__flush_access,
777 .finish_access = _unwind__finish_access,
778 .get_entries = _unwind__get_entries,
779};
780
781#ifndef REMOTE_UNWIND_LIBUNWIND
782struct unwind_libunwind_ops *
783local_unwind_libunwind_ops = &_unwind_libunwind_ops;
784#endif