symbol.c

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/*
 * Copyright (c) 2008 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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 <stdio.h>
#include <stdlib.h>

#include <rtld/rtld.h>
#include <rtld/rtld_debug.h>
#include <rtld/symbol.h>
#include <elf.h>

/*
 * Hash tables are 32-bit (elf_word) even for 64-bit ELF files.
 */
static elf_word elf_hash(const unsigned char *name)
{
        elf_word h = 0, g;

        while (*name) {
                h = (h << 4) + *name++;
                g = h & 0xf0000000;
                if (g != 0) h ^= g >> 24;
                h &= ~g;
        }

        return h;
}

static elf_symbol_t *def_find_in_module(const char *name, module_t *m)
{
        elf_symbol_t *sym_table;
        elf_symbol_t *s, *sym;
        elf_word nbucket;
        /*elf_word nchain;*/
        elf_word i;
        char *s_name;
        elf_word bucket;

        DPRINTF("def_find_in_module('%s', %s)\n", name, m->dyn.soname);

        sym_table = m->dyn.sym_tab;
        nbucket = m->dyn.hash[0];
        /*nchain = m->dyn.hash[1]; XXX Use to check HT range*/

        bucket = elf_hash((unsigned char *)name) % nbucket;
        i = m->dyn.hash[2 + bucket];

        sym = NULL;
        while (i != STN_UNDEF) {
                s = &sym_table[i];
                s_name = m->dyn.str_tab + s->st_name;

                if (str_cmp(name, s_name) == 0) {
                        sym = s;
                        break;
                }

                i = m->dyn.hash[2 + nbucket + i];
        }

        if (!sym)
                return NULL;    /* Not found */

        if (sym->st_shndx == SHN_UNDEF) {
                /* Not a definition */
                return NULL;
        }

        return sym; /* Found */
}

elf_symbol_t *symbol_bfs_find(const char *name, module_t *start, module_t **mod)
{
        module_t *m, *dm;
        elf_symbol_t *sym, *s;
        link_t queue_head;
        size_t i;

        /*
         * Do a BFS using the queue_link and bfs_tag fields.
         * Vertices (modules) are tagged the moment they are inserted
         * into the queue. This prevents from visiting the same vertex
         * more times in case of circular dependencies.
         */

        /* Mark all vertices (modules) as unvisited */  
        modules_untag();

        /* Insert root (the program) into the queue and tag it */
        list_initialize(&queue_head);
        start->bfs_tag = true;
        list_append(&start->queue_link, &queue_head);

        /* If the symbol is found, it will be stored in 'sym' */
        sym = NULL;

        /* While queue is not empty */
        while (!list_empty(&queue_head)) {
                /* Pop first element from the queue */
                m = list_get_instance(queue_head.next, module_t, queue_link);
                list_remove(&m->queue_link);

                s = def_find_in_module(name, m);
                if (s != NULL) {
                        /* Symbol found */
                        sym = s;
                        *mod = m;
                        break;
                }

                /*
                 * Insert m's untagged dependencies into the queue
                 * and tag them.
                 */
                for (i = 0; i < m->n_deps; ++i) {
                        dm = m->deps[i];

                        if (dm->bfs_tag == false) {
                                dm->bfs_tag = true;
                                list_append(&dm->queue_link, &queue_head);
                        }
                }
        }

        /* Empty the queue so that we leave it in a clean state */
        while (!list_empty(&queue_head))
                list_remove(queue_head.next);

        if (!sym) {
                return NULL; /* Not found */
        }

        return sym; /* Symbol found */
}


elf_symbol_t *symbol_def_find(const char *name, module_t *origin, module_t **mod)
{
        elf_symbol_t *s;

        if (origin->dyn.symbolic) {
                /* 
                 * Origin module has a DT_SYMBOLIC flag.
                 * Try this module first
                 */
                 s = def_find_in_module(name, origin);
                 if (s != NULL) {
                        /* Found */
                        *mod = origin;
                        return s;
                 }
        }

        /* Not DT_SYMBOLIC or no match. Now try other locations. */

        if (runtime_env->program) {
                /* Program is dynamic -- start with program as root. */
                return symbol_bfs_find(name, runtime_env->program, mod);
        } else {
                /* Program is static -- start with @a origin as root. */
                return symbol_bfs_find(name, origin, mod);
        }
}

void *symbol_get_addr(elf_symbol_t *sym, module_t *m)
{
        if (sym->st_shndx == SHN_ABS) {
                /* Do not add bias to absolute symbols */
                return (void *) sym->st_value;
        } else {
                return (void *) (sym->st_value + m->bias);
        }
}

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