unwind-libdw.c

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// SPDX-License-Identifier: GPL-2.0
#include <linux/compiler.h>
#include <elfutils/libdw.h>
#include <elfutils/libdwfl.h>
#include <inttypes.h>
#include <errno.h>
#include "debug.h"
#include "unwind.h"
#include "unwind-libdw.h"
#include "machine.h"
#include "thread.h"
#include <linux/types.h>
#include "event.h"
#include "perf_regs.h"
#include "callchain.h"
#include "util.h"

static char *debuginfo_path;

static const Dwfl_Callbacks offline_callbacks = {
    .find_debuginfo     = dwfl_standard_find_debuginfo,
    .debuginfo_path     = &debuginfo_path,
    .section_address    = dwfl_offline_section_address,
};

static int __report_module(struct addr_location *al, u64 ip,
                struct unwind_info *ui)
{
    Dwfl_Module *mod;
    struct dso *dso = NULL;
    /*
     * Some callers will use al->sym, so we can't just use the
     * cheaper thread__find_map() here.
     */
    thread__find_symbol(ui->thread, PERF_RECORD_MISC_USER, ip, al);

    if (al->map)
        dso = al->map->dso;

    if (!dso)
        return 0;

    mod = dwfl_addrmodule(ui->dwfl, ip);
    if (mod) {
        Dwarf_Addr s;

        dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
        if (s != al->map->start)
            mod = 0;
    }

    if (!mod)
        mod = dwfl_report_elf(ui->dwfl, dso->short_name,
                      (dso->symsrc_filename ? dso->symsrc_filename : dso->long_name), -1, al->map->start,
                      false);

    return mod && dwfl_addrmodule(ui->dwfl, ip) == mod ? 0 : -1;
}

static int report_module(u64 ip, struct unwind_info *ui)
{
    struct addr_location al;

    return __report_module(&al, ip, ui);
}

/*
 * Store all entries within entries array,
 * we will process it after we finish unwind.
 */
static int entry(u64 ip, struct unwind_info *ui)

{
    struct unwind_entry *e = &ui->entries[ui->idx++];
    struct addr_location al;

    if (__report_module(&al, ip, ui))
        return -1;

    e->ip  = al.addr;
    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 0;
}

static pid_t next_thread(Dwfl *dwfl, void *arg, void **thread_argp)
{
    /* We want only single thread to be processed. */
    if (*thread_argp != NULL)
        return 0;

    *thread_argp = arg;
    return dwfl_pid(dwfl);
}

static int access_dso_mem(struct unwind_info *ui, Dwarf_Addr addr,
              Dwarf_Word *data)
{
    struct addr_location al;
    ssize_t size;

    if (!thread__find_map(ui->thread, PERF_RECORD_MISC_USER, addr, &al)) {
        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 bool memory_read(Dwfl *dwfl __maybe_unused, Dwarf_Addr addr, Dwarf_Word *result,
            void *arg)
{
    struct unwind_info *ui = arg;
    struct stack_dump *stack = &ui->sample->user_stack;
    u64 start, end;
    int offset;
    int ret;

    ret = perf_reg_value(&start, &ui->sample->user_regs, PERF_REG_SP);
    if (ret)
        return false;

    end = start + stack->size;

    /* Check overflow. */
    if (addr + sizeof(Dwarf_Word) < addr)
        return false;

    if (addr < start || addr + sizeof(Dwarf_Word) > end) {
        ret = access_dso_mem(ui, addr, result);
        if (ret) {
            pr_debug("unwind: access_mem 0x%" PRIx64 " not inside range"
                 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
                addr, start, end);
            return false;
        }
        return true;
    }

    offset  = addr - start;
    *result = *(Dwarf_Word *)&stack->data[offset];
    pr_debug("unwind: access_mem addr 0x%" PRIx64 ", val %lx, offset %d\n",
         addr, (unsigned long)*result, offset);
    return true;
}

static const Dwfl_Thread_Callbacks callbacks = {
    .next_thread        = next_thread,
    .memory_read        = memory_read,
    .set_initial_registers  = libdw__arch_set_initial_registers,
};

static int
frame_callback(Dwfl_Frame *state, void *arg)
{
    struct unwind_info *ui = arg;
    Dwarf_Addr pc;
    bool isactivation;

    if (!dwfl_frame_pc(state, &pc, NULL)) {
        pr_err("%s", dwfl_errmsg(-1));
        return DWARF_CB_ABORT;
    }

    // report the module before we query for isactivation
    report_module(pc, ui);

    if (!dwfl_frame_pc(state, &pc, &isactivation)) {
        pr_err("%s", dwfl_errmsg(-1));
        return DWARF_CB_ABORT;
    }

    if (!isactivation)
        --pc;

    return entry(pc, ui) || !(--ui->max_stack) ?
           DWARF_CB_ABORT : DWARF_CB_OK;
}

int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
            struct thread *thread,
            struct perf_sample *data,
            int max_stack)
{
    struct unwind_info *ui, ui_buf = {
        .sample     = data,
        .thread     = thread,
        .machine    = thread->mg->machine,
        .cb     = cb,
        .arg        = arg,
        .max_stack  = max_stack,
    };
    Dwarf_Word ip;
    int err = -EINVAL, i;

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

    ui = zalloc(sizeof(ui_buf) + sizeof(ui_buf.entries[0]) * max_stack);
    if (!ui)
        return -ENOMEM;

    *ui = ui_buf;

    ui->dwfl = dwfl_begin(&offline_callbacks);
    if (!ui->dwfl)
        goto out;

    err = perf_reg_value(&ip, &data->user_regs, PERF_REG_IP);
    if (err)
        goto out;

    err = report_module(ip, ui);
    if (err)
        goto out;

    err = !dwfl_attach_state(ui->dwfl, EM_NONE, thread->tid, &callbacks, ui);
    if (err)
        goto out;

    err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);

    if (err && ui->max_stack != max_stack)
        err = 0;

    /*
     * Display what we got based on the order setup.
     */
    for (i = 0; i < ui->idx && !err; i++) {
        int j = i;

        if (callchain_param.order == ORDER_CALLER)
            j = ui->idx - i - 1;

        err = ui->entries[j].ip ? ui->cb(&ui->entries[j], ui->arg) : 0;
    }

 out:
    if (err)
        pr_debug("unwind: failed with '%s'\n", dwfl_errmsg(-1));

    dwfl_end(ui->dwfl);
    free(ui);
    return 0;
}