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1// SPDX-License-Identifier: GPL-2.02/*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 of6 * the libunwind 0.99 code which are (amongst other contributors I may have7 * forgotten):8 *9 * Copyright (C) 2002-2007 Hewlett-Packard Co10 * 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_LIBUNWIND30#include <libunwind.h>31#include <libunwind-ptrace.h>32#endif33#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 int45UNW_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 int54UNW_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 0xff67#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 by79 * GCC, presumably they aren't documented by LSB since they aren't80 * 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 0x8087 * #define DW_EH_PE_uleb128 0x0188 * #define DW_EH_PE_udata2 0x0289 * #define DW_EH_PE_sleb128 0x0990 * #define DW_EH_PE_sdata2 0x0a91 * #define DW_EH_PE_textrel 0x2092 * #define DW_EH_PE_datarel 0x3093 */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_FRAME198static 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#endif208 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_FRAME232static 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#endif252 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 the266 * 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 305struct read_unwind_spec_eh_frame_maps_cb_args {306 struct dso *dso;307 u64 base_addr;308};309 310static int read_unwind_spec_eh_frame_maps_cb(struct map *map, void *data)311{312 313 struct read_unwind_spec_eh_frame_maps_cb_args *args = data;314 315 if (map__dso(map) == args->dso && map__start(map) - map__pgoff(map) < args->base_addr)316 args->base_addr = map__start(map) - map__pgoff(map);317 318 return 0;319}320 321 322static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,323 u64 *table_data, u64 *segbase,324 u64 *fde_count)325{326 struct read_unwind_spec_eh_frame_maps_cb_args args = {327 .dso = dso,328 .base_addr = UINT64_MAX,329 };330 int ret, fd;331 332 if (dso__data(dso)->eh_frame_hdr_offset == 0) {333 fd = dso__data_get_fd(dso, ui->machine);334 if (fd < 0)335 return -EINVAL;336 337 /* Check the .eh_frame section for unwinding info */338 ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",339 &dso__data(dso)->eh_frame_hdr_addr,340 &dso__data(dso)->eh_frame_hdr_offset);341 dso__data(dso)->elf_base_addr = elf_base_address(fd);342 dso__data_put_fd(dso);343 if (ret || dso__data(dso)->eh_frame_hdr_offset == 0)344 return -EINVAL;345 }346 347 maps__for_each_map(thread__maps(ui->thread), read_unwind_spec_eh_frame_maps_cb, &args);348 349 args.base_addr -= dso__data(dso)->elf_base_addr;350 /* Address of .eh_frame_hdr */351 *segbase = args.base_addr + dso__data(dso)->eh_frame_hdr_addr;352 ret = unwind_spec_ehframe(dso, ui->machine, dso__data(dso)->eh_frame_hdr_offset,353 table_data, fde_count);354 if (ret)355 return ret;356 /* binary_search_table offset plus .eh_frame_hdr address */357 *table_data += *segbase;358 return 0;359}360 361#ifndef NO_LIBUNWIND_DEBUG_FRAME362static int read_unwind_spec_debug_frame(struct dso *dso,363 struct machine *machine, u64 *offset)364{365 int fd;366 u64 ofs = dso__data(dso)->debug_frame_offset;367 368 /* debug_frame can reside in:369 * - dso370 * - debug pointed by symsrc_filename371 * - gnu_debuglink, which doesn't necessary372 * has to be pointed by symsrc_filename373 */374 if (ofs == 0) {375 fd = dso__data_get_fd(dso, machine);376 if (fd >= 0) {377 ofs = elf_section_offset(fd, ".debug_frame");378 dso__data_put_fd(dso);379 }380 381 if (ofs <= 0) {382 fd = open(dso__symsrc_filename(dso), O_RDONLY);383 if (fd >= 0) {384 ofs = elf_section_offset(fd, ".debug_frame");385 close(fd);386 }387 }388 389 if (ofs <= 0) {390 char *debuglink = malloc(PATH_MAX);391 int ret = 0;392 393 if (debuglink == NULL) {394 pr_err("unwind: Can't read unwind spec debug frame.\n");395 return -ENOMEM;396 }397 398 ret = dso__read_binary_type_filename(399 dso, DSO_BINARY_TYPE__DEBUGLINK,400 machine->root_dir, debuglink, PATH_MAX);401 if (!ret) {402 fd = open(debuglink, O_RDONLY);403 if (fd >= 0) {404 ofs = elf_section_offset(fd,405 ".debug_frame");406 close(fd);407 }408 }409 if (ofs > 0) {410 if (dso__symsrc_filename(dso) != NULL) {411 pr_warning(412 "%s: overwrite symsrc(%s,%s)\n",413 __func__,414 dso__symsrc_filename(dso),415 debuglink);416 dso__free_symsrc_filename(dso);417 }418 dso__set_symsrc_filename(dso, debuglink);419 } else {420 free(debuglink);421 }422 }423 424 dso__data(dso)->debug_frame_offset = ofs;425 }426 427 *offset = ofs;428 if (*offset)429 return 0;430 431 return -EINVAL;432}433#endif434 435static struct map *find_map(unw_word_t ip, struct unwind_info *ui)436{437 struct addr_location al;438 struct map *ret;439 440 addr_location__init(&al);441 thread__find_map(ui->thread, PERF_RECORD_MISC_USER, ip, &al);442 ret = map__get(al.map);443 addr_location__exit(&al);444 return ret;445}446 447static int448find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,449 int need_unwind_info, void *arg)450{451 struct unwind_info *ui = arg;452 struct map *map;453 struct dso *dso;454 unw_dyn_info_t di;455 u64 table_data, segbase, fde_count;456 int ret = -EINVAL;457 458 map = find_map(ip, ui);459 if (!map)460 return -EINVAL;461 462 dso = map__dso(map);463 if (!dso) {464 map__put(map);465 return -EINVAL;466 }467 468 pr_debug("unwind: find_proc_info dso %s\n", dso__name(dso));469 470 /* Check the .eh_frame section for unwinding info */471 if (!read_unwind_spec_eh_frame(dso, ui, &table_data, &segbase, &fde_count)) {472 memset(&di, 0, sizeof(di));473 di.format = UNW_INFO_FORMAT_REMOTE_TABLE;474 di.start_ip = map__start(map);475 di.end_ip = map__end(map);476 di.u.rti.segbase = segbase;477 di.u.rti.table_data = table_data;478 di.u.rti.table_len = fde_count * sizeof(struct table_entry)479 / sizeof(unw_word_t);480 ret = dwarf_search_unwind_table(as, ip, &di, pi,481 need_unwind_info, arg);482 }483 484#ifndef NO_LIBUNWIND_DEBUG_FRAME485 /* Check the .debug_frame section for unwinding info */486 if (ret < 0 &&487 !read_unwind_spec_debug_frame(dso, ui->machine, &segbase)) {488 int fd = dso__data_get_fd(dso, ui->machine);489 int is_exec = elf_is_exec(fd, dso__name(dso));490 u64 start = map__start(map);491 unw_word_t base = is_exec ? 0 : start;492 const char *symfile;493 494 if (fd >= 0)495 dso__data_put_fd(dso);496 497 symfile = dso__symsrc_filename(dso) ?: dso__name(dso);498 499 memset(&di, 0, sizeof(di));500 if (dwarf_find_debug_frame(0, &di, ip, base, symfile, start, map__end(map)))501 ret = dwarf_search_unwind_table(as, ip, &di, pi,502 need_unwind_info, arg);503 }504#endif505 map__put(map);506 return ret;507}508 509static int access_fpreg(unw_addr_space_t __maybe_unused as,510 unw_regnum_t __maybe_unused num,511 unw_fpreg_t __maybe_unused *val,512 int __maybe_unused __write,513 void __maybe_unused *arg)514{515 pr_err("unwind: access_fpreg unsupported\n");516 return -UNW_EINVAL;517}518 519static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,520 unw_word_t __maybe_unused *dil_addr,521 void __maybe_unused *arg)522{523 return -UNW_ENOINFO;524}525 526static int resume(unw_addr_space_t __maybe_unused as,527 unw_cursor_t __maybe_unused *cu,528 void __maybe_unused *arg)529{530 pr_err("unwind: resume unsupported\n");531 return -UNW_EINVAL;532}533 534static int535get_proc_name(unw_addr_space_t __maybe_unused as,536 unw_word_t __maybe_unused addr,537 char __maybe_unused *bufp, size_t __maybe_unused buf_len,538 unw_word_t __maybe_unused *offp, void __maybe_unused *arg)539{540 pr_err("unwind: get_proc_name unsupported\n");541 return -UNW_EINVAL;542}543 544static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,545 unw_word_t *data)546{547 struct map *map;548 struct dso *dso;549 ssize_t size;550 551 map = find_map(addr, ui);552 if (!map) {553 pr_debug("unwind: no map for %lx\n", (unsigned long)addr);554 return -1;555 }556 557 dso = map__dso(map);558 559 if (!dso) {560 map__put(map);561 return -1;562 }563 564 size = dso__data_read_addr(dso, map, ui->machine,565 addr, (u8 *) data, sizeof(*data));566 map__put(map);567 return !(size == sizeof(*data));568}569 570static int access_mem(unw_addr_space_t __maybe_unused as,571 unw_word_t addr, unw_word_t *valp,572 int __write, void *arg)573{574 struct unwind_info *ui = arg;575 const char *arch = perf_env__arch(ui->machine->env);576 struct stack_dump *stack = &ui->sample->user_stack;577 u64 start, end;578 int offset;579 int ret;580 581 /* Don't support write, probably not needed. */582 if (__write || !stack || !ui->sample->user_regs.regs) {583 *valp = 0;584 return 0;585 }586 587 ret = perf_reg_value(&start, &ui->sample->user_regs,588 perf_arch_reg_sp(arch));589 if (ret)590 return ret;591 592 end = start + stack->size;593 594 /* Check overflow. */595 if (addr + sizeof(unw_word_t) < addr)596 return -EINVAL;597 598 if (addr < start || addr + sizeof(unw_word_t) >= end) {599 ret = access_dso_mem(ui, addr, valp);600 if (ret) {601 pr_debug("unwind: access_mem %p not inside range"602 " 0x%" PRIx64 "-0x%" PRIx64 "\n",603 (void *) (uintptr_t) addr, start, end);604 *valp = 0;605 return ret;606 }607 return 0;608 }609 610 offset = addr - start;611 *valp = *(unw_word_t *)&stack->data[offset];612 pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",613 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);614 return 0;615}616 617static int access_reg(unw_addr_space_t __maybe_unused as,618 unw_regnum_t regnum, unw_word_t *valp,619 int __write, void *arg)620{621 struct unwind_info *ui = arg;622 int id, ret;623 u64 val;624 625 /* Don't support write, I suspect we don't need it. */626 if (__write) {627 pr_err("unwind: access_reg w %d\n", regnum);628 return 0;629 }630 631 if (!ui->sample->user_regs.regs) {632 *valp = 0;633 return 0;634 }635 636 id = LIBUNWIND__ARCH_REG_ID(regnum);637 if (id < 0)638 return -EINVAL;639 640 ret = perf_reg_value(&val, &ui->sample->user_regs, id);641 if (ret) {642 if (!ui->best_effort)643 pr_err("unwind: can't read reg %d\n", regnum);644 return ret;645 }646 647 *valp = (unw_word_t) val;648 pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);649 return 0;650}651 652static void put_unwind_info(unw_addr_space_t __maybe_unused as,653 unw_proc_info_t *pi __maybe_unused,654 void *arg __maybe_unused)655{656 pr_debug("unwind: put_unwind_info called\n");657}658 659static int entry(u64 ip, struct thread *thread,660 unwind_entry_cb_t cb, void *arg)661{662 struct unwind_entry e;663 struct addr_location al;664 int ret;665 666 addr_location__init(&al);667 e.ms.sym = thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);668 e.ip = ip;669 e.ms.map = al.map;670 e.ms.maps = al.maps;671 672 pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",673 al.sym ? al.sym->name : "''",674 ip,675 al.map ? map__map_ip(al.map, ip) : (u64) 0);676 677 ret = cb(&e, arg);678 addr_location__exit(&al);679 return ret;680}681 682static void display_error(int err)683{684 switch (err) {685 case UNW_EINVAL:686 pr_err("unwind: Only supports local.\n");687 break;688 case UNW_EUNSPEC:689 pr_err("unwind: Unspecified error.\n");690 break;691 case UNW_EBADREG:692 pr_err("unwind: Register unavailable.\n");693 break;694 default:695 break;696 }697}698 699static unw_accessors_t accessors = {700 .find_proc_info = find_proc_info,701 .put_unwind_info = put_unwind_info,702 .get_dyn_info_list_addr = get_dyn_info_list_addr,703 .access_mem = access_mem,704 .access_reg = access_reg,705 .access_fpreg = access_fpreg,706 .resume = resume,707 .get_proc_name = get_proc_name,708};709 710static int _unwind__prepare_access(struct maps *maps)711{712 void *addr_space = unw_create_addr_space(&accessors, 0);713 714 maps__set_addr_space(maps, addr_space);715 if (!addr_space) {716 pr_err("unwind: Can't create unwind address space.\n");717 return -ENOMEM;718 }719 720 unw_set_caching_policy(addr_space, UNW_CACHE_GLOBAL);721 return 0;722}723 724static void _unwind__flush_access(struct maps *maps)725{726 unw_flush_cache(maps__addr_space(maps), 0, 0);727}728 729static void _unwind__finish_access(struct maps *maps)730{731 unw_destroy_addr_space(maps__addr_space(maps));732}733 734static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,735 void *arg, int max_stack)736{737 const char *arch = perf_env__arch(ui->machine->env);738 u64 val;739 unw_word_t ips[max_stack];740 unw_addr_space_t addr_space;741 unw_cursor_t c;742 int ret, i = 0;743 744 ret = perf_reg_value(&val, &ui->sample->user_regs,745 perf_arch_reg_ip(arch));746 if (ret)747 return ret;748 749 ips[i++] = (unw_word_t) val;750 751 /*752 * If we need more than one entry, do the DWARF753 * unwind itself.754 */755 if (max_stack - 1 > 0) {756 WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");757 addr_space = maps__addr_space(thread__maps(ui->thread));758 759 if (addr_space == NULL)760 return -1;761 762 ret = unw_init_remote(&c, addr_space, ui);763 if (ret && !ui->best_effort)764 display_error(ret);765 766 while (!ret && (unw_step(&c) > 0) && i < max_stack) {767 unw_get_reg(&c, UNW_REG_IP, &ips[i]);768 769 /*770 * Decrement the IP for any non-activation frames.771 * this is required to properly find the srcline772 * for caller frames.773 * See also the documentation for dwfl_frame_pc(),774 * which this code tries to replicate.775 */776 if (unw_is_signal_frame(&c) <= 0)777 --ips[i];778 779 ++i;780 }781 782 max_stack = i;783 }784 785 /*786 * Display what we got based on the order setup.787 */788 for (i = 0; i < max_stack && !ret; i++) {789 int j = i;790 791 if (callchain_param.order == ORDER_CALLER)792 j = max_stack - i - 1;793 ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;794 }795 796 return ret;797}798 799static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,800 struct thread *thread,801 struct perf_sample *data, int max_stack,802 bool best_effort)803{804 struct unwind_info ui = {805 .sample = data,806 .thread = thread,807 .machine = maps__machine(thread__maps(thread)),808 .best_effort = best_effort809 };810 811 if (!data->user_regs.regs)812 return -EINVAL;813 814 if (max_stack <= 0)815 return -EINVAL;816 817 return get_entries(&ui, cb, arg, max_stack);818}819 820static struct unwind_libunwind_ops821_unwind_libunwind_ops = {822 .prepare_access = _unwind__prepare_access,823 .flush_access = _unwind__flush_access,824 .finish_access = _unwind__finish_access,825 .get_entries = _unwind__get_entries,826};827 828#ifndef REMOTE_UNWIND_LIBUNWIND829struct unwind_libunwind_ops *830local_unwind_libunwind_ops = &_unwind_libunwind_ops;831#endif832