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

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