tools/perf/util/unwind-libunwind-local.c

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