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 <errno.h>
  20 #include <gelf.h>
  21 #include <fcntl.h>
  22 #include <inttypes.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <sys/mman.h>
  26 #include <linux/list.h>
  27 #ifndef REMOTE_UNWIND_LIBUNWIND
  28 #include <libunwind.h>
  29 #include <libunwind-ptrace.h>
  30 #endif
  31 #include "callchain.h"
  32 #include "thread.h"
  33 #include "session.h"
  34 #include "perf_regs.h"
  35 #include "unwind.h"
  36 #include "symbol.h"
  37 #include "util.h"
  38 #include "debug.h"
  39 #include "asm/bug.h"
  40 #include "dso.h"
  41
  42 extern int
  43 UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
  44                                     unw_word_t ip,
  45                                     unw_dyn_info_t *di,
  46                                     unw_proc_info_t *pi,
  47                                     int need_unwind_info, void *arg);
  48
  49 #define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
  50
  51 extern int
  52 UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
  53                                  unw_word_t ip,
  54                                  unw_word_t segbase,
  55                                  const char *obj_name, unw_word_t start,
  56                                  unw_word_t end);
  57
  58 #define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
  59
  60 #define DW_EH_PE_FORMAT_MASK    0x0f    /* format of the encoded value */
  61 #define DW_EH_PE_APPL_MASK      0x70    /* how the value is to be applied */
  62
  63 /* Pointer-encoding formats: */
  64 #define DW_EH_PE_omit           0xff
  65 #define DW_EH_PE_ptr            0x00    /* pointer-sized unsigned value */
  66 #define DW_EH_PE_udata4         0x03    /* unsigned 32-bit value */
  67 #define DW_EH_PE_udata8         0x04    /* unsigned 64-bit value */
  68 #define DW_EH_PE_sdata4         0x0b    /* signed 32-bit value */
  69 #define DW_EH_PE_sdata8         0x0c    /* signed 64-bit value */
  70
  71 /* Pointer-encoding application: */
  72 #define DW_EH_PE_absptr         0x00    /* absolute value */
  73 #define DW_EH_PE_pcrel          0x10    /* rel. to addr. of encoded value */
  74
  75 /*
  76  * The following are not documented by LSB v1.3, yet they are used by
  77  * GCC, presumably they aren't documented by LSB since they aren't
  78  * used on Linux:
  79  */
  80 #define DW_EH_PE_funcrel        0x40    /* start-of-procedure-relative */
  81 #define DW_EH_PE_aligned        0x50    /* aligned pointer */
  82
  83 /* Flags intentionaly not handled, since they're not needed:
  84  * #define DW_EH_PE_indirect      0x80
  85  * #define DW_EH_PE_uleb128       0x01
  86  * #define DW_EH_PE_udata2        0x02
  87  * #define DW_EH_PE_sleb128       0x09
  88  * #define DW_EH_PE_sdata2        0x0a
  89  * #define DW_EH_PE_textrel       0x20
  90  * #define DW_EH_PE_datarel       0x30
  91  */
  92
  93 struct unwind_info {
  94         struct perf_sample      *sample;
  95         struct machine          *machine;
  96         struct thread           *thread;
  97 };
  98
  99 #define dw_read(ptr, type, end) ({      \
 100         type *__p = (type *) ptr;       \
 101         type  __v;                      \
 102         if ((__p + 1) > (type *) end)   \
 103                 return -EINVAL;         \
 104         __v = *__p++;                   \
 105         ptr = (typeof(ptr)) __p;        \
 106         __v;                            \
 107         })
 108
 109 static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
 110                                    u8 encoding)
 111 {
 112         u8 *cur = *p;
 113         *val = 0;
 114
 115         switch (encoding) {
 116         case DW_EH_PE_omit:
 117                 *val = 0;
 118                 goto out;
 119         case DW_EH_PE_ptr:
 120                 *val = dw_read(cur, unsigned long, end);
 121                 goto out;
 122         default:
 123                 break;
 124         }
 125
 126         switch (encoding & DW_EH_PE_APPL_MASK) {
 127         case DW_EH_PE_absptr:
 128                 break;
 129         case DW_EH_PE_pcrel:
 130                 *val = (unsigned long) cur;
 131                 break;
 132         default:
 133                 return -EINVAL;
 134         }
 135
 136         if ((encoding & 0x07) == 0x00)
 137                 encoding |= DW_EH_PE_udata4;
 138
 139         switch (encoding & DW_EH_PE_FORMAT_MASK) {
 140         case DW_EH_PE_sdata4:
 141                 *val += dw_read(cur, s32, end);
 142                 break;
 143         case DW_EH_PE_udata4:
 144                 *val += dw_read(cur, u32, end);
 145                 break;
 146         case DW_EH_PE_sdata8:
 147                 *val += dw_read(cur, s64, end);
 148                 break;
 149         case DW_EH_PE_udata8:
 150                 *val += dw_read(cur, u64, end);
 151                 break;
 152         default:
 153                 return -EINVAL;
 154         }
 155
 156  out:
 157         *p = cur;
 158         return 0;
 159 }
 160
 161 #define dw_read_encoded_value(ptr, end, enc) ({                 \
 162         u64 __v;                                                \
 163         if (__dw_read_encoded_value(&ptr, end, &__v, enc)) {    \
 164                 return -EINVAL;                                 \
 165         }                                                       \
 166         __v;                                                    \
 167         })
 168
 169 static u64 elf_section_offset(int fd, const char *name)
 170 {
 171         Elf *elf;
 172         GElf_Ehdr ehdr;
 173         GElf_Shdr shdr;
 174         u64 offset = 0;
 175
 176         elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 177         if (elf == NULL)
 178                 return 0;
 179
 180         do {
 181                 if (gelf_getehdr(elf, &ehdr) == NULL)
 182                         break;
 183
 184                 if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
 185                         break;
 186
 187                 offset = shdr.sh_offset;
 188         } while (0);
 189
 190         elf_end(elf);
 191         return offset;
 192 }
 193
 194 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 195 static int elf_is_exec(int fd, const char *name)
 196 {
 197         Elf *elf;
 198         GElf_Ehdr ehdr;
 199         int retval = 0;
 200
 201         elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 202         if (elf == NULL)
 203                 return 0;
 204         if (gelf_getehdr(elf, &ehdr) == NULL)
 205                 goto out;
 206
 207         retval = (ehdr.e_type == ET_EXEC);
 208
 209 out:
 210         elf_end(elf);
 211         pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
 212         return retval;
 213 }
 214 #endif
 215
 216 struct table_entry {
 217         u32 start_ip_offset;
 218         u32 fde_offset;
 219 };
 220
 221 struct eh_frame_hdr {
 222         unsigned char version;
 223         unsigned char eh_frame_ptr_enc;
 224         unsigned char fde_count_enc;
 225         unsigned char table_enc;
 226
 227         /*
 228          * The rest of the header is variable-length and consists of the
 229          * following members:
 230          *
 231          *      encoded_t eh_frame_ptr;
 232          *      encoded_t fde_count;
 233          */
 234
 235         /* A single encoded pointer should not be more than 8 bytes. */
 236         u64 enc[2];
 237
 238         /*
 239          * struct {
 240          *    encoded_t start_ip;
 241          *    encoded_t fde_addr;
 242          * } binary_search_table[fde_count];
 243          */
 244         char data[0];
 245 } __packed;
 246
 247 static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
 248                                u64 offset, u64 *table_data, u64 *segbase,
 249                                u64 *fde_count)
 250 {
 251         struct eh_frame_hdr hdr;
 252         u8 *enc = (u8 *) &hdr.enc;
 253         u8 *end = (u8 *) &hdr.data;
 254         ssize_t r;
 255
 256         r = dso__data_read_offset(dso, machine, offset,
 257                                   (u8 *) &hdr, sizeof(hdr));
 258         if (r != sizeof(hdr))
 259                 return -EINVAL;
 260
 261         /* We dont need eh_frame_ptr, just skip it. */
 262         dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
 263
 264         *fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
 265         *segbase    = offset;
 266         *table_data = (enc - (u8 *) &hdr) + offset;
 267         return 0;
 268 }
 269
 270 static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
 271                                      u64 *table_data, u64 *segbase,
 272                                      u64 *fde_count)
 273 {
 274         int ret = -EINVAL, fd;
 275         u64 offset = dso->data.eh_frame_hdr_offset;
 276
 277         if (offset == 0) {
 278                 fd = dso__data_get_fd(dso, machine);
 279                 if (fd < 0)
 280                         return -EINVAL;
 281
 282                 /* Check the .eh_frame section for unwinding info */
 283                 offset = elf_section_offset(fd, ".eh_frame_hdr");
 284                 dso->data.eh_frame_hdr_offset = offset;
 285                 dso__data_put_fd(dso);
 286         }
 287
 288         if (offset)
 289                 ret = unwind_spec_ehframe(dso, machine, offset,
 290                                           table_data, segbase,
 291                                           fde_count);
 292
 293         return ret;
 294 }
 295
 296 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 297 static int read_unwind_spec_debug_frame(struct dso *dso,
 298                                         struct machine *machine, u64 *offset)
 299 {
 300         int fd;
 301         u64 ofs = dso->data.debug_frame_offset;
 302
 303         /* debug_frame can reside in:
 304          *  - dso
 305          *  - debug pointed by symsrc_filename
 306          *  - gnu_debuglink, which doesn't necessary
 307          *    has to be pointed by symsrc_filename
 308          */
 309         if (ofs == 0) {
 310                 fd = dso__data_get_fd(dso, machine);
 311                 if (fd >= 0) {
 312                         ofs = elf_section_offset(fd, ".debug_frame");
 313                         dso__data_put_fd(dso);
 314                 }
 315
 316                 if (ofs <= 0) {
 317                         fd = open(dso->symsrc_filename, O_RDONLY);
 318                         if (fd >= 0) {
 319                                 ofs = elf_section_offset(fd, ".debug_frame");
 320                                 close(fd);
 321                         }
 322                 }
 323
 324                 if (ofs <= 0) {
 325                         char *debuglink = malloc(PATH_MAX);
 326                         int ret = 0;
 327
 328                         ret = dso__read_binary_type_filename(
 329                                 dso, DSO_BINARY_TYPE__DEBUGLINK,
 330                                 machine->root_dir, debuglink, PATH_MAX);
 331                         if (!ret) {
 332                                 fd = open(debuglink, O_RDONLY);
 333                                 if (fd >= 0) {
 334                                         ofs = elf_section_offset(fd,
 335                                                         ".debug_frame");
 336                                         close(fd);
 337                                 }
 338                         }
 339                         if (ofs > 0) {
 340                                 if (dso->symsrc_filename != NULL) {
 341                                         pr_warning(
 342                                                 "%s: overwrite symsrc(%s,%s)\n",
 343                                                         __func__,
 344                                                         dso->symsrc_filename,
 345                                                         debuglink);
 346                                         free(dso->symsrc_filename);
 347                                 }
 348                                 dso->symsrc_filename = debuglink;
 349                         } else {
 350                                 free(debuglink);
 351                         }
 352                 }
 353
 354                 dso->data.debug_frame_offset = ofs;
 355         }
 356
 357         *offset = ofs;
 358         if (*offset)
 359                 return 0;
 360
 361         return -EINVAL;
 362 }
 363 #endif
 364
 365 static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
 366 {
 367         struct addr_location al;
 368
 369         thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
 370                               MAP__FUNCTION, ip, &al);
 371         if (!al.map) {
 372                 /*
 373                  * We've seen cases (softice) where DWARF unwinder went
 374                  * through non executable mmaps, which we need to lookup
 375                  * in MAP__VARIABLE tree.
 376                  */
 377                 thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
 378                                       MAP__VARIABLE, ip, &al);
 379         }
 380         return al.map;
 381 }
 382
 383 static int
 384 find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
 385                int need_unwind_info, void *arg)
 386 {
 387         struct unwind_info *ui = arg;
 388         struct map *map;
 389         unw_dyn_info_t di;
 390         u64 table_data, segbase, fde_count;
 391         int ret = -EINVAL;
 392
 393         map = find_map(ip, ui);
 394         if (!map || !map->dso)
 395                 return -EINVAL;
 396
 397         pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
 398
 399         /* Check the .eh_frame section for unwinding info */
 400         if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
 401                                        &table_data, &segbase, &fde_count)) {
 402                 memset(&di, 0, sizeof(di));
 403                 di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
 404                 di.start_ip = map->start;
 405                 di.end_ip   = map->end;
 406                 di.u.rti.segbase    = map->start + segbase - map->pgoff;
 407                 di.u.rti.table_data = map->start + table_data - map->pgoff;
 408                 di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
 409                                       / sizeof(unw_word_t);
 410                 ret = dwarf_search_unwind_table(as, ip, &di, pi,
 411                                                 need_unwind_info, arg);
 412         }
 413
 414 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 415         /* Check the .debug_frame section for unwinding info */
 416         if (ret < 0 &&
 417             !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
 418                 int fd = dso__data_get_fd(map->dso, ui->machine);
 419                 int is_exec = elf_is_exec(fd, map->dso->name);
 420                 unw_word_t base = is_exec ? 0 : map->start;
 421                 const char *symfile;
 422
 423                 if (fd >= 0)
 424                         dso__data_put_fd(map->dso);
 425
 426                 symfile = map->dso->symsrc_filename ?: map->dso->name;
 427
 428                 memset(&di, 0, sizeof(di));
 429                 if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
 430                                            map->start, map->end))
 431                         return dwarf_search_unwind_table(as, ip, &di, pi,
 432                                                          need_unwind_info, arg);
 433         }
 434 #endif
 435
 436         return ret;
 437 }
 438
 439 static int access_fpreg(unw_addr_space_t __maybe_unused as,
 440                         unw_regnum_t __maybe_unused num,
 441                         unw_fpreg_t __maybe_unused *val,
 442                         int __maybe_unused __write,
 443                         void __maybe_unused *arg)
 444 {
 445         pr_err("unwind: access_fpreg unsupported\n");
 446         return -UNW_EINVAL;
 447 }
 448
 449 static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
 450                                   unw_word_t __maybe_unused *dil_addr,
 451                                   void __maybe_unused *arg)
 452 {
 453         return -UNW_ENOINFO;
 454 }
 455
 456 static int resume(unw_addr_space_t __maybe_unused as,
 457                   unw_cursor_t __maybe_unused *cu,
 458                   void __maybe_unused *arg)
 459 {
 460         pr_err("unwind: resume unsupported\n");
 461         return -UNW_EINVAL;
 462 }
 463
 464 static int
 465 get_proc_name(unw_addr_space_t __maybe_unused as,
 466               unw_word_t __maybe_unused addr,
 467                 char __maybe_unused *bufp, size_t __maybe_unused buf_len,
 468                 unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
 469 {
 470         pr_err("unwind: get_proc_name unsupported\n");
 471         return -UNW_EINVAL;
 472 }
 473
 474 static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
 475                           unw_word_t *data)
 476 {
 477         struct map *map;
 478         ssize_t size;
 479
 480         map = find_map(addr, ui);
 481         if (!map) {
 482                 pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
 483                 return -1;
 484         }
 485
 486         if (!map->dso)
 487                 return -1;
 488
 489         size = dso__data_read_addr(map->dso, map, ui->machine,
 490                                    addr, (u8 *) data, sizeof(*data));
 491
 492         return !(size == sizeof(*data));
 493 }
 494
 495 static int access_mem(unw_addr_space_t __maybe_unused as,
 496                       unw_word_t addr, unw_word_t *valp,
 497                       int __write, void *arg)
 498 {
 499         struct unwind_info *ui = arg;
 500         struct stack_dump *stack = &ui->sample->user_stack;
 501         u64 start, end;
 502         int offset;
 503         int ret;
 504
 505         /* Don't support write, probably not needed. */
 506         if (__write || !stack || !ui->sample->user_regs.regs) {
 507                 *valp = 0;
 508                 return 0;
 509         }
 510
 511         ret = perf_reg_value(&start, &ui->sample->user_regs,
 512                              LIBUNWIND__ARCH_REG_SP);
 513         if (ret)
 514                 return ret;
 515
 516         end = start + stack->size;
 517
 518         /* Check overflow. */
 519         if (addr + sizeof(unw_word_t) < addr)
 520                 return -EINVAL;
 521
 522         if (addr < start || addr + sizeof(unw_word_t) >= end) {
 523                 ret = access_dso_mem(ui, addr, valp);
 524                 if (ret) {
 525                         pr_debug("unwind: access_mem %p not inside range"
 526                                  " 0x%" PRIx64 "-0x%" PRIx64 "\n",
 527                                  (void *) (uintptr_t) addr, start, end);
 528                         *valp = 0;
 529                         return ret;
 530                 }
 531                 return 0;
 532         }
 533
 534         offset = addr - start;
 535         *valp  = *(unw_word_t *)&stack->data[offset];
 536         pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
 537                  (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
 538         return 0;
 539 }
 540
 541 static int access_reg(unw_addr_space_t __maybe_unused as,
 542                       unw_regnum_t regnum, unw_word_t *valp,
 543                       int __write, void *arg)
 544 {
 545         struct unwind_info *ui = arg;
 546         int id, ret;
 547         u64 val;
 548
 549         /* Don't support write, I suspect we don't need it. */
 550         if (__write) {
 551                 pr_err("unwind: access_reg w %d\n", regnum);
 552                 return 0;
 553         }
 554
 555         if (!ui->sample->user_regs.regs) {
 556                 *valp = 0;
 557                 return 0;
 558         }
 559
 560         id = LIBUNWIND__ARCH_REG_ID(regnum);
 561         if (id < 0)
 562                 return -EINVAL;
 563
 564         ret = perf_reg_value(&val, &ui->sample->user_regs, id);
 565         if (ret) {
 566                 pr_err("unwind: can't read reg %d\n", regnum);
 567                 return ret;
 568         }
 569
 570         *valp = (unw_word_t) val;
 571         pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
 572         return 0;
 573 }
 574
 575 static void put_unwind_info(unw_addr_space_t __maybe_unused as,
 576                             unw_proc_info_t *pi __maybe_unused,
 577                             void *arg __maybe_unused)
 578 {
 579         pr_debug("unwind: put_unwind_info called\n");
 580 }
 581
 582 static int entry(u64 ip, struct thread *thread,
 583                  unwind_entry_cb_t cb, void *arg)
 584 {
 585         struct unwind_entry e;
 586         struct addr_location al;
 587
 588         thread__find_addr_location(thread, PERF_RECORD_MISC_USER,
 589                                    MAP__FUNCTION, ip, &al);
 590
 591         e.ip = al.addr;
 592         e.map = al.map;
 593         e.sym = al.sym;
 594
 595         pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
 596                  al.sym ? al.sym->name : "''",
 597                  ip,
 598                  al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
 599
 600         return cb(&e, arg);
 601 }
 602
 603 static void display_error(int err)
 604 {
 605         switch (err) {
 606         case UNW_EINVAL:
 607                 pr_err("unwind: Only supports local.\n");
 608                 break;
 609         case UNW_EUNSPEC:
 610                 pr_err("unwind: Unspecified error.\n");
 611                 break;
 612         case UNW_EBADREG:
 613                 pr_err("unwind: Register unavailable.\n");
 614                 break;
 615         default:
 616                 break;
 617         }
 618 }
 619
 620 static unw_accessors_t accessors = {
 621         .find_proc_info         = find_proc_info,
 622         .put_unwind_info        = put_unwind_info,
 623         .get_dyn_info_list_addr = get_dyn_info_list_addr,
 624         .access_mem             = access_mem,
 625         .access_reg             = access_reg,
 626         .access_fpreg           = access_fpreg,
 627         .resume                 = resume,
 628         .get_proc_name          = get_proc_name,
 629 };
 630
 631 static int _unwind__prepare_access(struct thread *thread)
 632 {
 633         if (callchain_param.record_mode != CALLCHAIN_DWARF)
 634                 return 0;
 635
 636         thread->addr_space = unw_create_addr_space(&accessors, 0);
 637         if (!thread->addr_space) {
 638                 pr_err("unwind: Can't create unwind address space.\n");
 639                 return -ENOMEM;
 640         }
 641
 642         unw_set_caching_policy(thread->addr_space, UNW_CACHE_GLOBAL);
 643         return 0;
 644 }
 645
 646 static void _unwind__flush_access(struct thread *thread)
 647 {
 648         if (callchain_param.record_mode != CALLCHAIN_DWARF)
 649                 return;
 650
 651         unw_flush_cache(thread->addr_space, 0, 0);
 652 }
 653
 654 static void _unwind__finish_access(struct thread *thread)
 655 {
 656         if (callchain_param.record_mode != CALLCHAIN_DWARF)
 657                 return;
 658
 659         unw_destroy_addr_space(thread->addr_space);
 660 }
 661
 662 static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
 663                        void *arg, int max_stack)
 664 {
 665         u64 val;
 666         unw_word_t ips[max_stack];
 667         unw_addr_space_t addr_space;
 668         unw_cursor_t c;
 669         int ret, i = 0;
 670
 671         ret = perf_reg_value(&val, &ui->sample->user_regs,
 672                              LIBUNWIND__ARCH_REG_IP);
 673         if (ret)
 674                 return ret;
 675
 676         ips[i++] = (unw_word_t) val;
 677
 678         /*
 679          * If we need more than one entry, do the DWARF
 680          * unwind itself.
 681          */
 682         if (max_stack - 1 > 0) {
 683                 WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
 684                 addr_space = ui->thread->addr_space;
 685
 686                 if (addr_space == NULL)
 687                         return -1;
 688
 689                 ret = unw_init_remote(&c, addr_space, ui);
 690                 if (ret)
 691                         display_error(ret);
 692
 693                 while (!ret && (unw_step(&c) > 0) && i < max_stack) {
 694                         unw_get_reg(&c, UNW_REG_IP, &ips[i]);
 695
 696                         /*
 697                          * Decrement the IP for any non-activation frames.
 698                          * this is required to properly find the srcline
 699                          * for caller frames.
 700                          * See also the documentation for dwfl_frame_pc(),
 701                          * which this code tries to replicate.
 702                          */
 703                         if (unw_is_signal_frame(&c) <= 0)
 704                                 --ips[i];
 705
 706                         ++i;
 707                 }
 708
 709                 max_stack = i;
 710         }
 711
 712         /*
 713          * Display what we got based on the order setup.
 714          */
 715         for (i = 0; i < max_stack && !ret; i++) {
 716                 int j = i;
 717
 718                 if (callchain_param.order == ORDER_CALLER)
 719                         j = max_stack - i - 1;
 720                 ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
 721         }
 722
 723         return ret;
 724 }
 725
 726 static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
 727                         struct thread *thread,
 728                         struct perf_sample *data, int max_stack)
 729 {
 730         struct unwind_info ui = {
 731                 .sample       = data,
 732                 .thread       = thread,
 733                 .machine      = thread->mg->machine,
 734         };
 735
 736         if (!data->user_regs.regs)
 737                 return -EINVAL;
 738
 739         if (max_stack <= 0)
 740                 return -EINVAL;
 741
 742         return get_entries(&ui, cb, arg, max_stack);
 743 }
 744
 745 static struct unwind_libunwind_ops
 746 _unwind_libunwind_ops = {
 747         .prepare_access = _unwind__prepare_access,
 748         .flush_access   = _unwind__flush_access,
 749         .finish_access  = _unwind__finish_access,
 750         .get_entries    = _unwind__get_entries,
 751 };
 752
 753 #ifndef REMOTE_UNWIND_LIBUNWIND
 754 struct unwind_libunwind_ops *
 755 local_unwind_libunwind_ops = &_unwind_libunwind_ops;
 756 #endif