/*      $NetBSD: ksyms.c,v 1.3 2024/04/01 18:33:24 riastradh Exp $      */

/*
 * Copyright (c) 2010,2011,2012 YAMAMOTO Takashi,
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: ksyms.c,v 1.3 2024/04/01 18:33:24 riastradh Exp $");
#endif /* not lint */

#include <assert.h>
#include <err.h>
#include <fcntl.h>
#include <gelf.h>
#include <libelf.h>
#include <paths.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <util.h>
#include "ksyms.h"

static struct sym **syms = NULL;
static size_t nsyms = 0;

static int
compare_value(const void *p1, const void *p2)
{
        const struct sym *s1 = *(const struct sym * const *)p1;
        const struct sym *s2 = *(const struct sym * const *)p2;

        if (s1->value > s2->value) {
                return -1;
        } else if (s1->value < s2->value) {
                return 1;
        }
        /*
         * to produce a stable result, it's better not to return 0
         * even for __strong_alias.
         */
        if (s1->size > s2->size) {
                return -1;
        } else if (s1->size < s2->size) {
                return 1;
        }
        return strcmp(s1->name, s2->name);
}

struct sym **
ksymload(size_t *nsymp)
{
        Elf *e;
        Elf_Scn *s;
        GElf_Shdr sh_store;
        GElf_Shdr *sh;
        Elf_Data *d;
        int fd;
        size_t size, i;

        fd = open(_PATH_KSYMS, O_RDONLY);
        if (fd == -1) {
                err(EXIT_FAILURE, "open " _PATH_KSYMS);
        }
        if (elf_version(EV_CURRENT) == EV_NONE) {
                goto elffail;
        }
        e = elf_begin(fd, ELF_C_READ, NULL);
        if (e == NULL) {
                goto elffail;
        }
        for (s = elf_nextscn(e, NULL); s != NULL; s = elf_nextscn(e, s)) {
                sh = gelf_getshdr(s, &sh_store);
                if (sh == NULL) {
                        goto elffail;
                }
                if (sh->sh_type == SHT_SYMTAB) {
                        break;
                }
        }
        if (s == NULL) {
                errx(EXIT_FAILURE, "no symtab");
        }
        d = elf_getdata(s, NULL);
        if (d == NULL) {
                goto elffail;
        }
        assert(sh->sh_size == d->d_size);
        size = sh->sh_size / sh->sh_entsize;
        for (i = 1; i < size; i++) {
                GElf_Sym st_store;
                GElf_Sym *st;
                struct sym *sym;

                st = gelf_getsym(d, (int)i, &st_store);
                if (st == NULL) {
                        goto elffail;
                }
                if (GELF_ST_TYPE(st->st_info) != STT_FUNC) {
                        continue;
                }
                sym = emalloc(sizeof(*sym));
                sym->name = estrdup(elf_strptr(e, sh->sh_link, st->st_name));
                sym->value = (uint64_t)st->st_value;
                sym->size = st->st_size;
                nsyms++;
                syms = erealloc(syms, sizeof(*syms) * nsyms);
                syms[nsyms - 1] = sym;
        }
        elf_end(e);
        close(fd);
        qsort(syms, nsyms, sizeof(*syms), compare_value);
        if (nsymp != NULL)
                *nsymp = nsyms;
        return syms;
elffail:
        errx(EXIT_FAILURE, "libelf: %s", elf_errmsg(elf_errno()));
}

const char *
ksymlookup(uint64_t value, uint64_t *offset, size_t *n)
{
        size_t hi;
        size_t lo;
        size_t i;

        /*
         * try to find the smallest i for which syms[i]->value <= value.
         * syms[] is ordered by syms[]->value in the descending order.
         */

        hi = nsyms - 1;
        lo = 0;
        while (lo < hi) {
                const size_t mid = (lo + hi) / 2;
                const struct sym *sym = syms[mid];

                assert(syms[lo]->value >= sym->value);
                assert(sym->value >= syms[hi]->value);
                if (sym->value <= value) {
                        hi = mid;
                        continue;
                }
                lo = mid + 1;
        }
        assert(lo == nsyms - 1 || syms[lo]->value <= value);
        assert(lo == 0 || syms[lo - 1]->value > value);
        for (i = lo; i < nsyms; i++) {
                const struct sym *sym = syms[i];

                if (sym->value <= value &&
                    (sym->size == 0 || value - sym->value <= sym->size )) {
                        *offset = value - sym->value;
                        if (n != NULL)
                                *n = i;
                        return sym->name;
                }
                if (sym->size != 0 && sym->value + sym->size < value) {
                        break;
                }
        }
        return NULL;
}