// SPDX-License-Identifier: GPL-2.0
/*
 * Post mortem Dwarf CFI based unwinding on top of regs and stack dumps.
 *
 * Lots of this code have been borrowed or heavily inspired from parts of
 * the libunwind 0.99 code which are (amongst other contributors I may have
 * forgotten):
 *
 * Copyright (C) 2002-2007 Hewlett-Packard Co
 *      Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
 *
 * And the bugs have been added by:
 *
 * Copyright (C) 2010, Frederic Weisbecker <fweisbec@gmail.com>
 * Copyright (C) 2012, Jiri Olsa <jolsa@redhat.com>
 *
 */

#include <elf.h>
#include <errno.h>
#include <gelf.h>
#include <fcntl.h>
#include <inttypes.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <linux/list.h>
#include <linux/zalloc.h>
#ifndef REMOTE_UNWIND_LIBUNWIND
#include <libunwind.h>
#include <libunwind-ptrace.h>
#endif
#include "callchain.h"
#include "thread.h"
#include "session.h"
#include "perf_regs.h"
#include "unwind.h"
#include "map.h"
#include "symbol.h"
#include "debug.h"
#include "asm/bug.h"
#include "dso.h"

extern int
UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
                                    unw_word_t ip,
                                    unw_dyn_info_t *di,
                                    unw_proc_info_t *pi,
                                    int need_unwind_info, void *arg);

#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)

extern int
UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
                                 unw_word_t ip,
                                 unw_word_t segbase,
                                 const char *obj_name, unw_word_t start,
                                 unw_word_t end);

#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)

#define DW_EH_PE_FORMAT_MASK    0x0f    /* format of the encoded value */
#define DW_EH_PE_APPL_MASK      0x70    /* how the value is to be applied */

/* Pointer-encoding formats: */
#define DW_EH_PE_omit           0xff
#define DW_EH_PE_ptr            0x00    /* pointer-sized unsigned value */
#define DW_EH_PE_udata4         0x03    /* unsigned 32-bit value */
#define DW_EH_PE_udata8         0x04    /* unsigned 64-bit value */
#define DW_EH_PE_sdata4         0x0b    /* signed 32-bit value */
#define DW_EH_PE_sdata8         0x0c    /* signed 64-bit value */

/* Pointer-encoding application: */
#define DW_EH_PE_absptr         0x00    /* absolute value */
#define DW_EH_PE_pcrel          0x10    /* rel. to addr. of encoded value */

/*
 * The following are not documented by LSB v1.3, yet they are used by
 * GCC, presumably they aren't documented by LSB since they aren't
 * used on Linux:
 */
#define DW_EH_PE_funcrel        0x40    /* start-of-procedure-relative */
#define DW_EH_PE_aligned        0x50    /* aligned pointer */

/* Flags intentionally not handled, since they're not needed:
 * #define DW_EH_PE_indirect      0x80
 * #define DW_EH_PE_uleb128       0x01
 * #define DW_EH_PE_udata2        0x02
 * #define DW_EH_PE_sleb128       0x09
 * #define DW_EH_PE_sdata2        0x0a
 * #define DW_EH_PE_textrel       0x20
 * #define DW_EH_PE_datarel       0x30
 */

struct unwind_info {
        struct perf_sample      *sample;
        struct machine          *machine;
        struct thread           *thread;
        bool                     best_effort;
};

#define dw_read(ptr, type, end) ({      \
        type *__p = (type *) ptr;       \
        type  __v;                      \
        if ((__p + 1) > (type *) end)   \
                return -EINVAL;         \
        __v = *__p++;                   \
        ptr = (typeof(ptr)) __p;        \
        __v;                            \
        })

static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
                                   u8 encoding)
{
        u8 *cur = *p;
        *val = 0;

        switch (encoding) {
        case DW_EH_PE_omit:
                *val = 0;
                goto out;
        case DW_EH_PE_ptr:
                *val = dw_read(cur, unsigned long, end);
                goto out;
        default:
                break;
        }

        switch (encoding & DW_EH_PE_APPL_MASK) {
        case DW_EH_PE_absptr:
                break;
        case DW_EH_PE_pcrel:
                *val = (unsigned long) cur;
                break;
        default:
                return -EINVAL;
        }

        if ((encoding & 0x07) == 0x00)
                encoding |= DW_EH_PE_udata4;

        switch (encoding & DW_EH_PE_FORMAT_MASK) {
        case DW_EH_PE_sdata4:
                *val += dw_read(cur, s32, end);
                break;
        case DW_EH_PE_udata4:
                *val += dw_read(cur, u32, end);
                break;
        case DW_EH_PE_sdata8:
                *val += dw_read(cur, s64, end);
                break;
        case DW_EH_PE_udata8:
                *val += dw_read(cur, u64, end);
                break;
        default:
                return -EINVAL;
        }

 out:
        *p = cur;
        return 0;
}

#define dw_read_encoded_value(ptr, end, enc) ({                 \
        u64 __v;                                                \
        if (__dw_read_encoded_value(&ptr, end, &__v, enc)) {    \
                return -EINVAL;                                 \
        }                                                       \
        __v;                                                    \
        })

static int elf_section_address_and_offset(int fd, const char *name, u64 *address, u64 *offset)
{
        Elf *elf;
        GElf_Ehdr ehdr;
        GElf_Shdr shdr;
        int ret = -1;

        elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
        if (elf == NULL)
                return -1;

        if (gelf_getehdr(elf, &ehdr) == NULL)
                goto out_err;

        if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
                goto out_err;

        *address = shdr.sh_addr;
        *offset = shdr.sh_offset;
        ret = 0;
out_err:
        elf_end(elf);
        return ret;
}

#ifndef NO_LIBUNWIND_DEBUG_FRAME
static u64 elf_section_offset(int fd, const char *name)
{
        u64 address, offset = 0;

        if (elf_section_address_and_offset(fd, name, &address, &offset))
                return 0;

        return offset;
}
#endif

static u64 elf_base_address(int fd)
{
        Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
        GElf_Phdr phdr;
        u64 retval = 0;
        size_t i, phdrnum = 0;

        if (elf == NULL)
                return 0;
        (void)elf_getphdrnum(elf, &phdrnum);
        /* PT_LOAD segments are sorted by p_vaddr, so the first has the minimum p_vaddr. */
        for (i = 0; i < phdrnum; i++) {
                if (gelf_getphdr(elf, i, &phdr) && phdr.p_type == PT_LOAD) {
                        retval = phdr.p_vaddr & -getpagesize();
                        break;
                }
        }

        elf_end(elf);
        return retval;
}

#ifndef NO_LIBUNWIND_DEBUG_FRAME
static int elf_is_exec(int fd, const char *name)
{
        Elf *elf;
        GElf_Ehdr ehdr;
        int retval = 0;

        elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
        if (elf == NULL)
                return 0;
        if (gelf_getehdr(elf, &ehdr) == NULL)
                goto out;

        retval = (ehdr.e_type == ET_EXEC);

out:
        elf_end(elf);
        pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
        return retval;
}
#endif

struct table_entry {
        u32 start_ip_offset;
        u32 fde_offset;
};

struct eh_frame_hdr {
        unsigned char version;
        unsigned char eh_frame_ptr_enc;
        unsigned char fde_count_enc;
        unsigned char table_enc;

        /*
         * The rest of the header is variable-length and consists of the
         * following members:
         *
         *      encoded_t eh_frame_ptr;
         *      encoded_t fde_count;
         */

        /* A single encoded pointer should not be more than 8 bytes. */
        u64 enc[2];

        /*
         * struct {
         *    encoded_t start_ip;
         *    encoded_t fde_addr;
         * } binary_search_table[fde_count];
         */
        char data[];
} __packed;

static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
                               u64 offset, u64 *table_data_offset, u64 *fde_count)
{
        struct eh_frame_hdr hdr;
        u8 *enc = (u8 *) &hdr.enc;
        u8 *end = (u8 *) &hdr.data;
        ssize_t r;

        r = dso__data_read_offset(dso, machine, offset,
                                  (u8 *) &hdr, sizeof(hdr));
        if (r != sizeof(hdr))
                return -EINVAL;

        /* We dont need eh_frame_ptr, just skip it. */
        dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);

        *fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
        *table_data_offset = enc - (u8 *) &hdr;
        return 0;
}

struct read_unwind_spec_eh_frame_maps_cb_args {
        struct dso *dso;
        u64 base_addr;
};

static int read_unwind_spec_eh_frame_maps_cb(struct map *map, void *data)
{

        struct read_unwind_spec_eh_frame_maps_cb_args *args = data;

        if (map__dso(map) == args->dso && map__start(map) - map__pgoff(map) < args->base_addr)
                args->base_addr = map__start(map) - map__pgoff(map);

        return 0;
}


static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,
                                     u64 *table_data, u64 *segbase,
                                     u64 *fde_count)
{
        struct read_unwind_spec_eh_frame_maps_cb_args args = {
                .dso = dso,
                .base_addr = UINT64_MAX,
        };
        int ret, fd;

        if (dso__data(dso)->eh_frame_hdr_offset == 0) {
                if (!dso__data_get_fd(dso, ui->machine, &fd))
                        return -EINVAL;

                /* Check the .eh_frame section for unwinding info */
                ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",
                                                     &dso__data(dso)->eh_frame_hdr_addr,
                                                     &dso__data(dso)->eh_frame_hdr_offset);
                dso__data(dso)->elf_base_addr = elf_base_address(fd);
                dso__data_put_fd(dso);
                if (ret || dso__data(dso)->eh_frame_hdr_offset == 0)
                        return -EINVAL;
        }

        maps__for_each_map(thread__maps(ui->thread), read_unwind_spec_eh_frame_maps_cb, &args);

        args.base_addr -= dso__data(dso)->elf_base_addr;
        /* Address of .eh_frame_hdr */
        *segbase = args.base_addr + dso__data(dso)->eh_frame_hdr_addr;
        ret = unwind_spec_ehframe(dso, ui->machine, dso__data(dso)->eh_frame_hdr_offset,
                                   table_data, fde_count);
        if (ret)
                return ret;
        /* binary_search_table offset plus .eh_frame_hdr address */
        *table_data += *segbase;
        return 0;
}

#ifndef NO_LIBUNWIND_DEBUG_FRAME
static int read_unwind_spec_debug_frame(struct dso *dso,
                                        struct machine *machine, u64 *offset)
{
        int fd;
        u64 ofs = dso__data(dso)->debug_frame_offset;

        /* debug_frame can reside in:
         *  - dso
         *  - debug pointed by symsrc_filename
         *  - gnu_debuglink, which doesn't necessary
         *    has to be pointed by symsrc_filename
         */
        if (ofs == 0) {
                if (dso__data_get_fd(dso, machine, &fd)) {
                        ofs = elf_section_offset(fd, ".debug_frame");
                        dso__data_put_fd(dso);
                }

                if (ofs <= 0) {
                        fd = open(dso__symsrc_filename(dso), O_RDONLY);
                        if (fd >= 0) {
                                ofs = elf_section_offset(fd, ".debug_frame");
                                close(fd);
                        }
                }

                if (ofs <= 0) {
                        char *debuglink = malloc(PATH_MAX);
                        int ret = 0;

                        if (debuglink == NULL) {
                                pr_err("unwind: Can't read unwind spec debug frame.\n");
                                return -ENOMEM;
                        }

                        ret = dso__read_binary_type_filename(
                                dso, DSO_BINARY_TYPE__DEBUGLINK,
                                machine->root_dir, debuglink, PATH_MAX);
                        if (!ret) {
                                fd = open(debuglink, O_RDONLY);
                                if (fd >= 0) {
                                        ofs = elf_section_offset(fd,
                                                        ".debug_frame");
                                        close(fd);
                                }
                        }
                        if (ofs > 0) {
                                if (dso__symsrc_filename(dso) != NULL) {
                                        pr_warning(
                                                "%s: overwrite symsrc(%s,%s)\n",
                                                        __func__,
                                                        dso__symsrc_filename(dso),
                                                        debuglink);
                                        dso__free_symsrc_filename(dso);
                                }
                                dso__set_symsrc_filename(dso, debuglink);
                        } else {
                                free(debuglink);
                        }
                }

                dso__data(dso)->debug_frame_offset = ofs;
        }

        *offset = ofs;
        if (*offset)
                return 0;

        return -EINVAL;
}
#endif

static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
{
        struct addr_location al;
        struct map *ret;

        addr_location__init(&al);
        thread__find_map(ui->thread, PERF_RECORD_MISC_USER, ip, &al);
        ret = map__get(al.map);
        addr_location__exit(&al);
        return ret;
}

static int
find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
               int need_unwind_info, void *arg)
{
        struct unwind_info *ui = arg;
        struct map *map;
        struct dso *dso;
        unw_dyn_info_t di;
        u64 table_data, segbase, fde_count;
        int ret = -EINVAL;

        map = find_map(ip, ui);
        if (!map)
                return -EINVAL;

        dso = map__dso(map);
        if (!dso) {
                map__put(map);
                return -EINVAL;
        }

        pr_debug("unwind: find_proc_info dso %s\n", dso__name(dso));

        /* Check the .eh_frame section for unwinding info */
        if (!read_unwind_spec_eh_frame(dso, ui, &table_data, &segbase, &fde_count)) {
                memset(&di, 0, sizeof(di));
                di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
                di.start_ip = map__start(map);
                di.end_ip   = map__end(map);
                di.u.rti.segbase    = segbase;
                di.u.rti.table_data = table_data;
                di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
                                      / sizeof(unw_word_t);
                ret = dwarf_search_unwind_table(as, ip, &di, pi,
                                                need_unwind_info, arg);
        }

#ifndef NO_LIBUNWIND_DEBUG_FRAME
        /* Check the .debug_frame section for unwinding info */
        if (ret < 0 &&
            !read_unwind_spec_debug_frame(dso, ui->machine, &segbase)) {
                int fd;
                u64 start = map__start(map);
                unw_word_t base = start;
                const char *symfile;

                if (dso__data_get_fd(dso, ui->machine, &fd)) {
                        if (elf_is_exec(fd, dso__name(dso)))
                                base = 0;
                        dso__data_put_fd(dso);
                }

                symfile = dso__symsrc_filename(dso) ?: dso__name(dso);

                memset(&di, 0, sizeof(di));
                if (dwarf_find_debug_frame(0, &di, ip, base, symfile, start, map__end(map)))
                        ret = dwarf_search_unwind_table(as, ip, &di, pi,
                                                        need_unwind_info, arg);
        }
#endif
        map__put(map);
        return ret;
}

static int access_fpreg(unw_addr_space_t __maybe_unused as,
                        unw_regnum_t __maybe_unused num,
                        unw_fpreg_t __maybe_unused *val,
                        int __maybe_unused __write,
                        void __maybe_unused *arg)
{
        pr_err("unwind: access_fpreg unsupported\n");
        return -UNW_EINVAL;
}

static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
                                  unw_word_t __maybe_unused *dil_addr,
                                  void __maybe_unused *arg)
{
        return -UNW_ENOINFO;
}

static int resume(unw_addr_space_t __maybe_unused as,
                  unw_cursor_t __maybe_unused *cu,
                  void __maybe_unused *arg)
{
        pr_err("unwind: resume unsupported\n");
        return -UNW_EINVAL;
}

static int
get_proc_name(unw_addr_space_t __maybe_unused as,
              unw_word_t __maybe_unused addr,
                char __maybe_unused *bufp, size_t __maybe_unused buf_len,
                unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
{
        pr_err("unwind: get_proc_name unsupported\n");
        return -UNW_EINVAL;
}

static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
                          unw_word_t *data)
{
        struct map *map;
        struct dso *dso;
        ssize_t size;

        map = find_map(addr, ui);
        if (!map) {
                pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
                return -1;
        }

        dso = map__dso(map);

        if (!dso) {
                map__put(map);
                return -1;
        }

        size = dso__data_read_addr(dso, map, ui->machine,
                                   addr, (u8 *) data, sizeof(*data));
        map__put(map);
        return !(size == sizeof(*data));
}

static int access_mem(unw_addr_space_t __maybe_unused as,
                      unw_word_t addr, unw_word_t *valp,
                      int __write, void *arg)
{
        struct unwind_info *ui = arg;
        struct stack_dump *stack = &ui->sample->user_stack;
        u64 start, end;
        int offset;
        int ret;

        /* Don't support write, probably not needed. */
        if (__write || !stack || !ui->sample->user_regs || !ui->sample->user_regs->regs) {
                *valp = 0;
                return 0;
        }

        ret = perf_reg_value(&start, perf_sample__user_regs(ui->sample),
                             perf_arch_reg_sp(thread__e_machine(ui->thread,
                                                                ui->machine,
                                                                /*e_flags=*/NULL)));
        if (ret)
                return ret;

        end = start + stack->size;

        /* Check overflow. */
        if (addr + sizeof(unw_word_t) < addr)
                return -EINVAL;

        if (addr < start || addr + sizeof(unw_word_t) >= end) {
                ret = access_dso_mem(ui, addr, valp);
                if (ret) {
                        pr_debug("unwind: access_mem %p not inside range"
                                 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
                                 (void *) (uintptr_t) addr, start, end);
                        *valp = 0;
                        return ret;
                }
                return 0;
        }

        offset = addr - start;
        *valp  = *(unw_word_t *)&stack->data[offset];
        pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
                 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
        return 0;
}

static int access_reg(unw_addr_space_t __maybe_unused as,
                      unw_regnum_t regnum, unw_word_t *valp,
                      int __write, void *arg)
{
        struct unwind_info *ui = arg;
        int id, ret;
        u64 val;

        /* Don't support write, I suspect we don't need it. */
        if (__write) {
                pr_err("unwind: access_reg w %d\n", regnum);
                return 0;
        }

        if (!ui->sample->user_regs || !ui->sample->user_regs->regs) {
                *valp = 0;
                return 0;
        }

        id = LIBUNWIND__ARCH_REG_ID(regnum);
        if (id < 0)
                return -EINVAL;

        ret = perf_reg_value(&val, perf_sample__user_regs(ui->sample), id);
        if (ret) {
                if (!ui->best_effort)
                        pr_err("unwind: can't read reg %d\n", regnum);
                return ret;
        }

        *valp = (unw_word_t) val;
        pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
        return 0;
}

static void put_unwind_info(unw_addr_space_t __maybe_unused as,
                            unw_proc_info_t *pi __maybe_unused,
                            void *arg __maybe_unused)
{
        pr_debug("unwind: put_unwind_info called\n");
}

static int entry(u64 ip, struct thread *thread,
                 unwind_entry_cb_t cb, void *arg)
{
        struct unwind_entry e;
        struct addr_location al;
        int ret;

        addr_location__init(&al);
        e.ms.sym = thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
        e.ip     = ip;
        e.ms.map = al.map;
        e.ms.thread = thread__get(al.thread);

        pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
                 al.sym ? al.sym->name : "''",
                 ip,
                 al.map ? map__map_ip(al.map, ip) : (u64) 0);

        ret = cb(&e, arg);
        addr_location__exit(&al);
        return ret;
}

static void display_error(int err)
{
        switch (err) {
        case UNW_EINVAL:
                pr_err("unwind: Only supports local.\n");
                break;
        case UNW_EUNSPEC:
                pr_err("unwind: Unspecified error.\n");
                break;
        case UNW_EBADREG:
                pr_err("unwind: Register unavailable.\n");
                break;
        default:
                break;
        }
}

static unw_accessors_t accessors = {
        .find_proc_info         = find_proc_info,
        .put_unwind_info        = put_unwind_info,
        .get_dyn_info_list_addr = get_dyn_info_list_addr,
        .access_mem             = access_mem,
        .access_reg             = access_reg,
        .access_fpreg           = access_fpreg,
        .resume                 = resume,
        .get_proc_name          = get_proc_name,
};

static int _unwind__prepare_access(struct maps *maps)
{
        void *addr_space = unw_create_addr_space(&accessors, 0);

        maps__set_addr_space(maps, addr_space);
        if (!addr_space) {
                pr_err("unwind: Can't create unwind address space.\n");
                return -ENOMEM;
        }

        unw_set_caching_policy(addr_space, UNW_CACHE_GLOBAL);
        return 0;
}

static void _unwind__flush_access(struct maps *maps)
{
        unw_flush_cache(maps__addr_space(maps), 0, 0);
}

static void _unwind__finish_access(struct maps *maps)
{
        unw_destroy_addr_space(maps__addr_space(maps));
}

static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
                       void *arg, int max_stack)
{
        uint16_t e_machine = thread__e_machine(ui->thread, ui->machine, /*e_flags=*/NULL);
        u64 val;
        unw_word_t ips[max_stack];
        unw_addr_space_t addr_space;
        unw_cursor_t c;
        int ret, i = 0;

        ret = perf_reg_value(&val, perf_sample__user_regs(ui->sample),
                             perf_arch_reg_ip(e_machine));
        if (ret)
                return ret;

        ips[i++] = (unw_word_t) val;

        /*
         * If we need more than one entry, do the DWARF
         * unwind itself.
         */
        if (max_stack - 1 > 0) {
                WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
                addr_space = maps__addr_space(thread__maps(ui->thread));

                if (addr_space == NULL)
                        return -1;

                ret = unw_init_remote(&c, addr_space, ui);
                if (ret && !ui->best_effort)
                        display_error(ret);

                while (!ret && (unw_step(&c) > 0) && i < max_stack) {
                        unw_get_reg(&c, UNW_REG_IP, &ips[i]);

                        /*
                         * Decrement the IP for any non-activation frames.
                         * this is required to properly find the srcline
                         * for caller frames.
                         * See also the documentation for dwfl_frame_pc(),
                         * which this code tries to replicate.
                         */
                        if (unw_is_signal_frame(&c) <= 0)
                                --ips[i];

                        ++i;
                }

                max_stack = i;
        }

        /*
         * Display what we got based on the order setup.
         */
        for (i = 0; i < max_stack && !ret; i++) {
                int j = i;

                if (callchain_param.order == ORDER_CALLER)
                        j = max_stack - i - 1;
                ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
        }

        return ret;
}

static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
                        struct thread *thread,
                        struct perf_sample *data, int max_stack,
                        bool best_effort)
{
        struct unwind_info ui = {
                .sample       = data,
                .thread       = thread,
                .machine      = maps__machine(thread__maps(thread)),
                .best_effort  = best_effort
        };

        if (!data->user_regs || !data->user_regs->regs)
                return -EINVAL;

        if (max_stack <= 0)
                return -EINVAL;

        return get_entries(&ui, cb, arg, max_stack);
}

static struct unwind_libunwind_ops
_unwind_libunwind_ops = {
        .prepare_access = _unwind__prepare_access,
        .flush_access   = _unwind__flush_access,
        .finish_access  = _unwind__finish_access,
        .get_entries    = _unwind__get_entries,
};

#ifndef REMOTE_UNWIND_LIBUNWIND
struct unwind_libunwind_ops *
local_unwind_libunwind_ops = &_unwind_libunwind_ops;
#endif