unwind.c

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/*
 * 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 <[email protected]>
 *
 * And the bugs have been added by:
 *
 * Copyright (C) 2010, Frederic Weisbecker <[email protected]>
 * Copyright (C) 2012, Jiri Olsa <[email protected]>
 *
 */

#include <elf.h>
#include <gelf.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <linux/list.h>
#include <libunwind.h>
#include <libunwind-ptrace.h>
#include "thread.h"
#include "session.h"
#include "perf_regs.h"
#include "unwind.h"
#include "util.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)

#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 intentionaly 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;
    u64         sample_uregs;
};

#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 Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
                    GElf_Shdr *shp, const char *name)
{
    Elf_Scn *sec = NULL;

    while ((sec = elf_nextscn(elf, sec)) != NULL) {
        char *str;

        gelf_getshdr(sec, shp);
        str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
        if (!strcmp(name, str))
            break;
    }

    return sec;
}

static u64 elf_section_offset(int fd, const char *name)
{
    Elf *elf;
    GElf_Ehdr ehdr;
    GElf_Shdr shdr;
    u64 offset = 0;

    elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
    if (elf == NULL)
        return 0;

    do {
        if (gelf_getehdr(elf, &ehdr) == NULL)
            break;

        if (!elf_section_by_name(elf, &ehdr, &shdr, name))
            break;

        offset = shdr.sh_offset;
    } while (0);

    elf_end(elf);
    return offset;
}

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[0];
} __packed;

static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
                   u64 offset, u64 *table_data, u64 *segbase,
                   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);
    *segbase    = offset;
    *table_data = (enc - (u8 *) &hdr) + offset;
    return 0;
}

static int read_unwind_spec(struct dso *dso, struct machine *machine,
                u64 *table_data, u64 *segbase, u64 *fde_count)
{
    int ret = -EINVAL, fd;
    u64 offset;

    fd = dso__data_fd(dso, machine);
    if (fd < 0)
        return -EINVAL;

    offset = elf_section_offset(fd, ".eh_frame_hdr");
    close(fd);

    if (offset)
        ret = unwind_spec_ehframe(dso, machine, offset,
                      table_data, segbase,
                      fde_count);

    /* TODO .debug_frame check if eh_frame_hdr fails */
    return ret;
}

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

    thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
                  MAP__FUNCTION, ip, &al);
    return al.map;
}

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;
    unw_dyn_info_t di;
    u64 table_data, segbase, fde_count;

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

    pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);

    if (read_unwind_spec(map->dso, ui->machine,
                 &table_data, &segbase, &fde_count))
        return -EINVAL;

    memset(&di, 0, sizeof(di));
    di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
    di.start_ip = map->start;
    di.end_ip   = map->end;
    di.u.rti.segbase    = map->start + segbase;
    di.u.rti.table_data = map->start + table_data;
    di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
                  / sizeof(unw_word_t);
    return dwarf_search_unwind_table(as, ip, &di, pi,
                     need_unwind_info, arg);
}

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 addr_location al;
    ssize_t size;

    thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
                  MAP__FUNCTION, addr, &al);
    if (!al.map) {
        pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
        return -1;
    }

    if (!al.map->dso)
        return -1;

    size = dso__data_read_addr(al.map->dso, al.map, ui->machine,
                   addr, (u8 *) data, sizeof(*data));

    return !(size == sizeof(*data));
}

static int reg_value(unw_word_t *valp, struct regs_dump *regs, int id,
             u64 sample_regs)
{
    int i, idx = 0;

    if (!(sample_regs & (1 << id)))
        return -EINVAL;

    for (i = 0; i < id; i++) {
        if (sample_regs & (1 << i))
            idx++;
    }

    *valp = regs->regs[idx];
    return 0;
}

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;
    unw_word_t start, end;
    int offset;
    int ret;

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

    ret = reg_value(&start, &ui->sample->user_regs, PERF_REG_SP,
            ui->sample_uregs);
    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 %p-%p\n",
                (void *)addr, (void *)start, (void *)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 *)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;

    /* 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.regs) {
        *valp = 0;
        return 0;
    }

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

    ret = reg_value(valp, &ui->sample->user_regs, id, ui->sample_uregs);
    if (ret) {
        pr_err("unwind: can't read reg %d\n", regnum);
        return ret;
    }

    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, struct machine *machine,
         unwind_entry_cb_t cb, void *arg)
{
    struct unwind_entry e;
    struct addr_location al;

    thread__find_addr_location(thread, machine,
                   PERF_RECORD_MISC_USER,
                   MAP__FUNCTION, ip, &al, NULL);

    e.ip = ip;
    e.map = al.map;
    e.sym = al.sym;

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

    return cb(&e, arg);
}

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 get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
               void *arg)
{
    unw_addr_space_t addr_space;
    unw_cursor_t c;
    int ret;

    addr_space = unw_create_addr_space(&accessors, 0);
    if (!addr_space) {
        pr_err("unwind: Can't create unwind address space.\n");
        return -ENOMEM;
    }

    ret = unw_init_remote(&c, addr_space, ui);
    if (ret)
        display_error(ret);

    while (!ret && (unw_step(&c) > 0)) {
        unw_word_t ip;

        unw_get_reg(&c, UNW_REG_IP, &ip);
        ret = entry(ip, ui->thread, ui->machine, cb, arg);
    }

    unw_destroy_addr_space(addr_space);
    return ret;
}

int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
            struct machine *machine, struct thread *thread,
            u64 sample_uregs, struct perf_sample *data)
{
    unw_word_t ip;
    struct unwind_info ui = {
        .sample       = data,
        .sample_uregs = sample_uregs,
        .thread       = thread,
        .machine      = machine,
    };
    int ret;

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

    ret = reg_value(&ip, &data->user_regs, PERF_REG_IP, sample_uregs);
    if (ret)
        return ret;

    ret = entry(ip, thread, machine, cb, arg);
    if (ret)
        return -ENOMEM;

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