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 "debug.h"
  41 #include "asm/bug.h"
  42 #include "dso.h"
  43
  44 extern int
  45 UNW_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
  53 extern int
  54 UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
  55                                  unw_word_t ip,
  56                                  unw_word_t segbase,
  57                                  const char *obj_name, unw_word_t start,
  58                                  unw_word_t end);
  59
  60 #define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
  61
  62 #define DW_EH_PE_FORMAT_MASK    0x0f    /* format of the encoded value */
  63 #define DW_EH_PE_APPL_MASK      0x70    /* how the value is to be applied */
  64
  65 /* Pointer-encoding formats: */
  66 #define DW_EH_PE_omit           0xff
  67 #define DW_EH_PE_ptr            0x00    /* pointer-sized unsigned value */
  68 #define DW_EH_PE_udata4         0x03    /* unsigned 32-bit value */
  69 #define DW_EH_PE_udata8         0x04    /* unsigned 64-bit value */
  70 #define DW_EH_PE_sdata4         0x0b    /* signed 32-bit value */
  71 #define DW_EH_PE_sdata8         0x0c    /* signed 64-bit value */
  72
  73 /* Pointer-encoding application: */
  74 #define DW_EH_PE_absptr         0x00    /* absolute value */
  75 #define DW_EH_PE_pcrel          0x10    /* rel. to addr. of encoded value */
  76
  77 /*
  78  * The following are not documented by LSB v1.3, yet they are used by
  79  * GCC, presumably they aren't documented by LSB since they aren't
  80  * used on Linux:
  81  */
  82 #define DW_EH_PE_funcrel        0x40    /* start-of-procedure-relative */
  83 #define DW_EH_PE_aligned        0x50    /* aligned pointer */
  84
  85 /* Flags intentionally not handled, since they're not needed:
  86  * #define DW_EH_PE_indirect      0x80
  87  * #define DW_EH_PE_uleb128       0x01
  88  * #define DW_EH_PE_udata2        0x02
  89  * #define DW_EH_PE_sleb128       0x09
  90  * #define DW_EH_PE_sdata2        0x0a
  91  * #define DW_EH_PE_textrel       0x20
  92  * #define DW_EH_PE_datarel       0x30
  93  */
  94
  95 struct 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
 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 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;
 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;
 192 out_err:
 193         elf_end(elf);
 194         return ret;
 195 }
 196
 197 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 198 static u64 elf_section_offset(int fd, const char *name)
 199 {
 200         u64 address, offset;
 201
 202         if (elf_section_address_and_offset(fd, name, &address, &offset))
 203                 return 0;
 204
 205         return offset;
 206 }
 207 #endif
 208
 209 static u64 elf_base_address(int fd)
 210 {
 211         Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 212         GElf_Phdr phdr;
 213         u64 retval = 0;
 214         size_t i, phdrnum = 0;
 215
 216         if (elf == NULL)
 217                 return 0;
 218         (void)elf_getphdrnum(elf, &phdrnum);
 219         /* PT_LOAD segments are sorted by p_vaddr, so the first has the minimum p_vaddr. */
 220         for (i = 0; i < phdrnum; i++) {
 221                 if (gelf_getphdr(elf, i, &phdr) && phdr.p_type == PT_LOAD) {
 222                         retval = phdr.p_vaddr & -getpagesize();
 223                         break;
 224                 }
 225         }
 226
 227         elf_end(elf);
 228         return retval;
 229 }
 230
 231 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 232 static 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
 246 out:
 247         elf_end(elf);
 248         pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
 249         return retval;
 250 }
 251 #endif
 252
 253 struct table_entry {
 254         u32 start_ip_offset;
 255         u32 fde_offset;
 256 };
 257
 258 struct eh_frame_hdr {
 259         unsigned char version;
 260         unsigned char eh_frame_ptr_enc;
 261         unsigned char fde_count_enc;
 262         unsigned char table_enc;
 263
 264         /*
 265          * The rest of the header is variable-length and consists of the
 266          * following members:
 267          *
 268          *      encoded_t eh_frame_ptr;
 269          *      encoded_t fde_count;
 270          */
 271
 272         /* A single encoded pointer should not be more than 8 bytes. */
 273         u64 enc[2];
 274
 275         /*
 276          * struct {
 277          *    encoded_t start_ip;
 278          *    encoded_t fde_addr;
 279          * } binary_search_table[fde_count];
 280          */
 281         char data[];
 282 } __packed;
 283
 284 static 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
 305 static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,
 306                                      u64 *table_data, u64 *segbase,
 307                                      u64 *fde_count)
 308 {
 309         struct map *map;
 310         u64 base_addr = UINT64_MAX;
 311         int ret, fd;
 312
 313         if (dso->data.eh_frame_hdr_offset == 0) {
 314                 fd = dso__data_get_fd(dso, ui->machine);
 315                 if (fd < 0)
 316                         return -EINVAL;
 317
 318                 /* Check the .eh_frame section for unwinding info */
 319                 ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",
 320                                                      &dso->data.eh_frame_hdr_addr,
 321                                                      &dso->data.eh_frame_hdr_offset);
 322                 dso->data.elf_base_addr = elf_base_address(fd);
 323                 dso__data_put_fd(dso);
 324                 if (ret || dso->data.eh_frame_hdr_offset == 0)
 325                         return -EINVAL;
 326         }
 327
 328         maps__for_each_entry(ui->thread->maps, map) {
 329                 if (map->dso == dso && map->start < base_addr)
 330                         base_addr = map->start;
 331         }
 332         base_addr -= dso->data.elf_base_addr;
 333         /* Address of .eh_frame_hdr */
 334         *segbase = base_addr + dso->data.eh_frame_hdr_addr;
 335         ret = unwind_spec_ehframe(dso, ui->machine, dso->data.eh_frame_hdr_offset,
 336                                    table_data, fde_count);
 337         if (ret)
 338                 return ret;
 339         /* binary_search_table offset plus .eh_frame_hdr address */
 340         *table_data += *segbase;
 341         return 0;
 342 }
 343
 344 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 345 static int read_unwind_spec_debug_frame(struct dso *dso,
 346                                         struct machine *machine, u64 *offset)
 347 {
 348         int fd;
 349         u64 ofs = dso->data.debug_frame_offset;
 350
 351         /* debug_frame can reside in:
 352          *  - dso
 353          *  - debug pointed by symsrc_filename
 354          *  - gnu_debuglink, which doesn't necessary
 355          *    has to be pointed by symsrc_filename
 356          */
 357         if (ofs == 0) {
 358                 fd = dso__data_get_fd(dso, machine);
 359                 if (fd >= 0) {
 360                         ofs = elf_section_offset(fd, ".debug_frame");
 361                         dso__data_put_fd(dso);
 362                 }
 363
 364                 if (ofs <= 0) {
 365                         fd = open(dso->symsrc_filename, O_RDONLY);
 366                         if (fd >= 0) {
 367                                 ofs = elf_section_offset(fd, ".debug_frame");
 368                                 close(fd);
 369                         }
 370                 }
 371
 372                 if (ofs <= 0) {
 373                         char *debuglink = malloc(PATH_MAX);
 374                         int ret = 0;
 375
 376                         ret = dso__read_binary_type_filename(
 377                                 dso, DSO_BINARY_TYPE__DEBUGLINK,
 378                                 machine->root_dir, debuglink, PATH_MAX);
 379                         if (!ret) {
 380                                 fd = open(debuglink, O_RDONLY);
 381                                 if (fd >= 0) {
 382                                         ofs = elf_section_offset(fd,
 383                                                         ".debug_frame");
 384                                         close(fd);
 385                                 }
 386                         }
 387                         if (ofs > 0) {
 388                                 if (dso->symsrc_filename != NULL) {
 389                                         pr_warning(
 390                                                 "%s: overwrite symsrc(%s,%s)\n",
 391                                                         __func__,
 392                                                         dso->symsrc_filename,
 393                                                         debuglink);
 394                                         zfree(&dso->symsrc_filename);
 395                                 }
 396                                 dso->symsrc_filename = debuglink;
 397                         } else {
 398                                 free(debuglink);
 399                         }
 400                 }
 401
 402                 dso->data.debug_frame_offset = ofs;
 403         }
 404
 405         *offset = ofs;
 406         if (*offset)
 407                 return 0;
 408
 409         return -EINVAL;
 410 }
 411 #endif
 412
 413 static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
 414 {
 415         struct addr_location al;
 416         return thread__find_map(ui->thread, PERF_RECORD_MISC_USER, ip, &al);
 417 }
 418
 419 static int
 420 find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
 421                int need_unwind_info, void *arg)
 422 {
 423         struct unwind_info *ui = arg;
 424         struct map *map;
 425         unw_dyn_info_t di;
 426         u64 table_data, segbase, fde_count;
 427         int ret = -EINVAL;
 428
 429         map = find_map(ip, ui);
 430         if (!map || !map->dso)
 431                 return -EINVAL;
 432
 433         pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
 434
 435         /* Check the .eh_frame section for unwinding info */
 436         if (!read_unwind_spec_eh_frame(map->dso, ui,
 437                                        &table_data, &segbase, &fde_count)) {
 438                 memset(&di, 0, sizeof(di));
 439                 di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
 440                 di.start_ip = map->start;
 441                 di.end_ip   = map->end;
 442                 di.u.rti.segbase    = segbase;
 443                 di.u.rti.table_data = table_data;
 444                 di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
 445                                       / sizeof(unw_word_t);
 446                 ret = dwarf_search_unwind_table(as, ip, &di, pi,
 447                                                 need_unwind_info, arg);
 448         }
 449
 450 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 451         /* Check the .debug_frame section for unwinding info */
 452         if (ret < 0 &&
 453             !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
 454                 int fd = dso__data_get_fd(map->dso, ui->machine);
 455                 int is_exec = elf_is_exec(fd, map->dso->name);
 456                 unw_word_t base = is_exec ? 0 : map->start;
 457                 const char *symfile;
 458
 459                 if (fd >= 0)
 460                         dso__data_put_fd(map->dso);
 461
 462                 symfile = map->dso->symsrc_filename ?: map->dso->name;
 463
 464                 memset(&di, 0, sizeof(di));
 465                 if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
 466                                            map->start, map->end))
 467                         return dwarf_search_unwind_table(as, ip, &di, pi,
 468                                                          need_unwind_info, arg);
 469         }
 470 #endif
 471
 472         return ret;
 473 }
 474
 475 static int access_fpreg(unw_addr_space_t __maybe_unused as,
 476                         unw_regnum_t __maybe_unused num,
 477                         unw_fpreg_t __maybe_unused *val,
 478                         int __maybe_unused __write,
 479                         void __maybe_unused *arg)
 480 {
 481         pr_err("unwind: access_fpreg unsupported\n");
 482         return -UNW_EINVAL;
 483 }
 484
 485 static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
 486                                   unw_word_t __maybe_unused *dil_addr,
 487                                   void __maybe_unused *arg)
 488 {
 489         return -UNW_ENOINFO;
 490 }
 491
 492 static int resume(unw_addr_space_t __maybe_unused as,
 493                   unw_cursor_t __maybe_unused *cu,
 494                   void __maybe_unused *arg)
 495 {
 496         pr_err("unwind: resume unsupported\n");
 497         return -UNW_EINVAL;
 498 }
 499
 500 static int
 501 get_proc_name(unw_addr_space_t __maybe_unused as,
 502               unw_word_t __maybe_unused addr,
 503                 char __maybe_unused *bufp, size_t __maybe_unused buf_len,
 504                 unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
 505 {
 506         pr_err("unwind: get_proc_name unsupported\n");
 507         return -UNW_EINVAL;
 508 }
 509
 510 static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
 511                           unw_word_t *data)
 512 {
 513         struct map *map;
 514         ssize_t size;
 515
 516         map = find_map(addr, ui);
 517         if (!map) {
 518                 pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
 519                 return -1;
 520         }
 521
 522         if (!map->dso)
 523                 return -1;
 524
 525         size = dso__data_read_addr(map->dso, map, ui->machine,
 526                                    addr, (u8 *) data, sizeof(*data));
 527
 528         return !(size == sizeof(*data));
 529 }
 530
 531 static int access_mem(unw_addr_space_t __maybe_unused as,
 532                       unw_word_t addr, unw_word_t *valp,
 533                       int __write, void *arg)
 534 {
 535         struct unwind_info *ui = arg;
 536         struct stack_dump *stack = &ui->sample->user_stack;
 537         u64 start, end;
 538         int offset;
 539         int ret;
 540
 541         /* Don't support write, probably not needed. */
 542         if (__write || !stack || !ui->sample->user_regs.regs) {
 543                 *valp = 0;
 544                 return 0;
 545         }
 546
 547         ret = perf_reg_value(&start, &ui->sample->user_regs,
 548                              LIBUNWIND__ARCH_REG_SP);
 549         if (ret)
 550                 return ret;
 551
 552         end = start + stack->size;
 553
 554         /* Check overflow. */
 555         if (addr + sizeof(unw_word_t) < addr)
 556                 return -EINVAL;
 557
 558         if (addr < start || addr + sizeof(unw_word_t) >= end) {
 559                 ret = access_dso_mem(ui, addr, valp);
 560                 if (ret) {
 561                         pr_debug("unwind: access_mem %p not inside range"
 562                                  " 0x%" PRIx64 "-0x%" PRIx64 "\n",
 563                                  (void *) (uintptr_t) addr, start, end);
 564                         *valp = 0;
 565                         return ret;
 566                 }
 567                 return 0;
 568         }
 569
 570         offset = addr - start;
 571         *valp  = *(unw_word_t *)&stack->data[offset];
 572         pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
 573                  (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
 574         return 0;
 575 }
 576
 577 static int access_reg(unw_addr_space_t __maybe_unused as,
 578                       unw_regnum_t regnum, unw_word_t *valp,
 579                       int __write, void *arg)
 580 {
 581         struct unwind_info *ui = arg;
 582         int id, ret;
 583         u64 val;
 584
 585         /* Don't support write, I suspect we don't need it. */
 586         if (__write) {
 587                 pr_err("unwind: access_reg w %d\n", regnum);
 588                 return 0;
 589         }
 590
 591         if (!ui->sample->user_regs.regs) {
 592                 *valp = 0;
 593                 return 0;
 594         }
 595
 596         id = LIBUNWIND__ARCH_REG_ID(regnum);
 597         if (id < 0)
 598                 return -EINVAL;
 599
 600         ret = perf_reg_value(&val, &ui->sample->user_regs, id);
 601         if (ret) {
 602                 if (!ui->best_effort)
 603                         pr_err("unwind: can't read reg %d\n", regnum);
 604                 return ret;
 605         }
 606
 607         *valp = (unw_word_t) val;
 608         pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
 609         return 0;
 610 }
 611
 612 static void put_unwind_info(unw_addr_space_t __maybe_unused as,
 613                             unw_proc_info_t *pi __maybe_unused,
 614                             void *arg __maybe_unused)
 615 {
 616         pr_debug("unwind: put_unwind_info called\n");
 617 }
 618
 619 static int entry(u64 ip, struct thread *thread,
 620                  unwind_entry_cb_t cb, void *arg)
 621 {
 622         struct unwind_entry e;
 623         struct addr_location al;
 624
 625         e.ms.sym = thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
 626         e.ip     = ip;
 627         e.ms.map = al.map;
 628         e.ms.maps = al.maps;
 629
 630         pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
 631                  al.sym ? al.sym->name : "''",
 632                  ip,
 633                  al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
 634
 635         return cb(&e, arg);
 636 }
 637
 638 static void display_error(int err)
 639 {
 640         switch (err) {
 641         case UNW_EINVAL:
 642                 pr_err("unwind: Only supports local.\n");
 643                 break;
 644         case UNW_EUNSPEC:
 645                 pr_err("unwind: Unspecified error.\n");
 646                 break;
 647         case UNW_EBADREG:
 648                 pr_err("unwind: Register unavailable.\n");
 649                 break;
 650         default:
 651                 break;
 652         }
 653 }
 654
 655 static unw_accessors_t accessors = {
 656         .find_proc_info         = find_proc_info,
 657         .put_unwind_info        = put_unwind_info,
 658         .get_dyn_info_list_addr = get_dyn_info_list_addr,
 659         .access_mem             = access_mem,
 660         .access_reg             = access_reg,
 661         .access_fpreg           = access_fpreg,
 662         .resume                 = resume,
 663         .get_proc_name          = get_proc_name,
 664 };
 665
 666 static int _unwind__prepare_access(struct maps *maps)
 667 {
 668         maps->addr_space = unw_create_addr_space(&accessors, 0);
 669         if (!maps->addr_space) {
 670                 pr_err("unwind: Can't create unwind address space.\n");
 671                 return -ENOMEM;
 672         }
 673
 674         unw_set_caching_policy(maps->addr_space, UNW_CACHE_GLOBAL);
 675         return 0;
 676 }
 677
 678 static void _unwind__flush_access(struct maps *maps)
 679 {
 680         unw_flush_cache(maps->addr_space, 0, 0);
 681 }
 682
 683 static void _unwind__finish_access(struct maps *maps)
 684 {
 685         unw_destroy_addr_space(maps->addr_space);
 686 }
 687
 688 static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
 689                        void *arg, int max_stack)
 690 {
 691         u64 val;
 692         unw_word_t ips[max_stack];
 693         unw_addr_space_t addr_space;
 694         unw_cursor_t c;
 695         int ret, i = 0;
 696
 697         ret = perf_reg_value(&val, &ui->sample->user_regs,
 698                              LIBUNWIND__ARCH_REG_IP);
 699         if (ret)
 700                 return ret;
 701
 702         ips[i++] = (unw_word_t) val;
 703
 704         /*
 705          * If we need more than one entry, do the DWARF
 706          * unwind itself.
 707          */
 708         if (max_stack - 1 > 0) {
 709                 WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
 710                 addr_space = ui->thread->maps->addr_space;
 711
 712                 if (addr_space == NULL)
 713                         return -1;
 714
 715                 ret = unw_init_remote(&c, addr_space, ui);
 716                 if (ret && !ui->best_effort)
 717                         display_error(ret);
 718
 719                 while (!ret && (unw_step(&c) > 0) && i < max_stack) {
 720                         unw_get_reg(&c, UNW_REG_IP, &ips[i]);
 721
 722                         /*
 723                          * Decrement the IP for any non-activation frames.
 724                          * this is required to properly find the srcline
 725                          * for caller frames.
 726                          * See also the documentation for dwfl_frame_pc(),
 727                          * which this code tries to replicate.
 728                          */
 729                         if (unw_is_signal_frame(&c) <= 0)
 730                                 --ips[i];
 731
 732                         ++i;
 733                 }
 734
 735                 max_stack = i;
 736         }
 737
 738         /*
 739          * Display what we got based on the order setup.
 740          */
 741         for (i = 0; i < max_stack && !ret; i++) {
 742                 int j = i;
 743
 744                 if (callchain_param.order == ORDER_CALLER)
 745                         j = max_stack - i - 1;
 746                 ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
 747         }
 748
 749         return ret;
 750 }
 751
 752 static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
 753                         struct thread *thread,
 754                         struct perf_sample *data, int max_stack,
 755                         bool best_effort)
 756 {
 757         struct unwind_info ui = {
 758                 .sample       = data,
 759                 .thread       = thread,
 760                 .machine      = thread->maps->machine,
 761                 .best_effort  = best_effort
 762         };
 763
 764         if (!data->user_regs.regs)
 765                 return -EINVAL;
 766
 767         if (max_stack <= 0)
 768                 return -EINVAL;
 769
 770         return get_entries(&ui, cb, arg, max_stack);
 771 }
 772
 773 static struct unwind_libunwind_ops
 774 _unwind_libunwind_ops = {
 775         .prepare_access = _unwind__prepare_access,
 776         .flush_access   = _unwind__flush_access,
 777         .finish_access  = _unwind__finish_access,
 778         .get_entries    = _unwind__get_entries,
 779 };
 780
 781 #ifndef REMOTE_UNWIND_LIBUNWIND
 782 struct unwind_libunwind_ops *
 783 local_unwind_libunwind_ops = &_unwind_libunwind_ops;
 784 #endif