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  1. /*
  2.  * Copyright (c) 2008 Jiri Svoboda
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup rtld rtld
  30.  * @brief
  31.  * @{
  32.  */
  33. /**
  34.  * @file
  35.  */
  36.  
  37. #include <stdio.h>
  38. #include <stdlib.h>
  39. #include <string.h>
  40.  
  41. #include <rtld.h>
  42. #include <symbol.h>
  43. #include <elf.h>
  44.  
  45. /*
  46.  * Hash tables are 32-bit (elf_word) even for 64-bit ELF files.
  47.  */
  48. static elf_word elf_hash(const unsigned char *name)
  49. {
  50.     elf_word h = 0, g;
  51.  
  52.     while (*name) {
  53.         h = (h << 4) + *name++;
  54.         g = h & 0xf0000000;
  55.         if (g != 0) h ^= g >> 24;
  56.         h &= ~g;
  57.     }
  58.  
  59.     return h;
  60. }
  61.  
  62. static elf_symbol_t *def_find_in_module(char *name, module_t *m)
  63. {
  64.     elf_symbol_t *sym_table;
  65.     elf_symbol_t *s, *sym;
  66.     elf_word nbucket;
  67.     elf_word nchain;
  68.     elf_word i;
  69.     char *s_name;
  70.     elf_word bucket;
  71.  
  72. //  module_name = m->dyn.soname;
  73. //  DPRINTF("def_find_in_module('%s', %s)\n", name, module_name);
  74.  
  75.     sym_table = m->dyn.sym_tab;
  76.     nbucket = m->dyn.hash[0];
  77.     nchain = m->dyn.hash[1];
  78.  
  79.     bucket = elf_hash((unsigned char *)name) % nbucket;
  80.     i = m->dyn.hash[2 + bucket];
  81.  
  82.     sym = NULL;
  83.     while (i != STN_UNDEF) {
  84.         s = &sym_table[i];
  85.         s_name = m->dyn.str_tab + s->st_name;
  86.  
  87.         if (strcmp(name, s_name) == 0) {
  88.             sym = s;
  89.             break;
  90.         }
  91.  
  92.         i = m->dyn.hash[2 + nbucket + i];
  93.     }
  94.  
  95.     if (!sym)
  96.         return NULL;    /* Not found */
  97.  
  98.     if (sym->st_shndx == SHN_UNDEF) {
  99.         /* Not a definition */
  100.         return NULL;
  101.     }
  102.  
  103.     return sym; /* Found */
  104. }
  105.  
  106. /** Find the definition of a symbol.
  107.  *
  108.  * By definition in System V ABI, if module origin has the flag DT_SYMBOLIC,
  109.  * origin is searched first. Otherwise, or if the symbol hasn't been found,
  110.  * the module dependency graph is searched breadth-first, beginning
  111.  * from the executable program.
  112.  *
  113.  * @param name      Name of the symbol to search for.
  114.  * @param origin    Module in which the dependency originates.
  115.  * @param mod       (output) Will be filled with a pointer to the module
  116.  *          that contains the symbol.
  117.  */
  118. elf_symbol_t *symbol_def_find(char *name, module_t *origin, module_t **mod)
  119. {
  120.     module_t *m, *dm;
  121.     elf_symbol_t *sym, *s;
  122.     link_t queue_head;
  123.     size_t i;
  124.  
  125.     if (origin->dyn.symbolic) {
  126.         /*
  127.          * Origin module has a DT_SYMBOLIC flag.
  128.          * Try this module first
  129.          */
  130.          s = def_find_in_module(name, origin);
  131.          if (s != NULL) {
  132.             /* Found */
  133.             *mod = origin;
  134.             return s;
  135.          }
  136.     }
  137.  
  138.     /* Otherwise start in the executable program */
  139.  
  140.     /*
  141.      * Do a BFS using the queue_link and bfs_tag fields.
  142.      * Vertices (modules) are tagged the moment they are inserted
  143.      * into the queue. This prevents from visiting the same vertex
  144.      * more times in case of circular dependencies.
  145.      */
  146.  
  147.     /* Mark all vertices (modules) as unvisited */ 
  148.     modules_untag();
  149.  
  150.     /* Insert root (the program) into the queue and tag it */
  151.     list_initialize(&queue_head);
  152.     runtime_env->program->bfs_tag = true;
  153.     list_append(&runtime_env->program->queue_link, &queue_head);
  154.  
  155.     /* If the symbol is found, it will be stored in 'sym' */
  156.     sym = NULL;
  157.  
  158.     /* While queue is not empty */
  159.     while (!list_empty(&queue_head)) {
  160.         /* Pop first element from the queue */
  161.         m = list_get_instance(queue_head.next, module_t, queue_link);
  162.         list_remove(&m->queue_link);
  163.  
  164.         s = def_find_in_module(name, m);
  165.         if (s != NULL) {
  166.             /* Symbol found */
  167.             sym = s;
  168.             *mod = m;
  169.             break;
  170.         }
  171.  
  172.         /*
  173.          * Insert m's untagged dependencies into the queue
  174.          * and tag them.
  175.          */
  176.         for (i = 0; i < m->n_deps; ++i) {
  177.             dm = m->deps[i];
  178.  
  179.             if (dm->bfs_tag == false) {
  180.                 dm->bfs_tag = true;
  181.                 list_append(&dm->queue_link, &queue_head);
  182.             }
  183.         }
  184.     }
  185.  
  186.     /* Empty the queue so that we leave it in a clean state */
  187.     while (!list_empty(&queue_head))
  188.         list_remove(queue_head.next);
  189.  
  190.     if (!sym) {
  191.         printf("Error, symbol '%s' not found anywhere\n", name);
  192.         exit(1);
  193.         return NULL; /* Not found */
  194.     }
  195.  
  196.     return sym; /* Symbol found */
  197. }
  198.  
  199. uintptr_t symbol_get_addr(elf_symbol_t *sym, module_t *m)
  200. {
  201.     if (sym->st_shndx == SHN_ABS) {
  202.         /* Do not add bias to absolute symbols */
  203.         return sym->st_value;
  204.     } else {
  205.         return sym->st_value + m->bias;
  206.     }
  207. }
  208.  
  209. /** @}
  210.  */
  211.