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3960
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1 /*
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2 * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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25 #include <unistd.h>
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26 #include <search.h>
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27 #include <stdlib.h>
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28 #include <string.h>
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29 #include <db.h>
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30 #include <fcntl.h>
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31 #include "symtab.h"
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32 #include "salibelf.h"
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33
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34
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35 // ----------------------------------------------------
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36 // functions for symbol lookups
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37 // ----------------------------------------------------
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38
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39 struct elf_section {
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40 ELF_SHDR *c_shdr;
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41 void *c_data;
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42 };
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43
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44 struct elf_symbol {
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45 char *name;
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46 uintptr_t offset;
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47 uintptr_t size;
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48 };
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49
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50 typedef struct symtab {
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51 char *strs;
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52 size_t num_symbols;
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53 struct elf_symbol *symbols;
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54 DB* hash_table;
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55 } symtab_t;
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56
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57 // read symbol table from given fd.
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58 struct symtab* build_symtab(int fd) {
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59 ELF_EHDR ehdr;
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60 struct symtab* symtab = NULL;
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61
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62 // Reading of elf header
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63 struct elf_section *scn_cache = NULL;
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64 int cnt = 0;
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65 ELF_SHDR* shbuf = NULL;
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66 ELF_SHDR* cursct = NULL;
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67 ELF_PHDR* phbuf = NULL;
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68 int symtab_found = 0;
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69 int dynsym_found = 0;
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70 uint32_t symsection = SHT_SYMTAB;
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71
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72 uintptr_t baseaddr = (uintptr_t)-1;
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73
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74 lseek(fd, (off_t)0L, SEEK_SET);
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75 if (! read_elf_header(fd, &ehdr)) {
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76 // not an elf
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77 return NULL;
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78 }
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79
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80 // read ELF header
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81 if ((shbuf = read_section_header_table(fd, &ehdr)) == NULL) {
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82 goto quit;
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83 }
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84
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85 baseaddr = find_base_address(fd, &ehdr);
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86
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87 scn_cache = calloc(ehdr.e_shnum, sizeof(*scn_cache));
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88 if (scn_cache == NULL) {
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89 goto quit;
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90 }
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91
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92 for (cursct = shbuf, cnt = 0; cnt < ehdr.e_shnum; cnt++) {
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93 scn_cache[cnt].c_shdr = cursct;
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94 if (cursct->sh_type == SHT_SYMTAB ||
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95 cursct->sh_type == SHT_STRTAB ||
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96 cursct->sh_type == SHT_DYNSYM) {
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97 if ( (scn_cache[cnt].c_data = read_section_data(fd, &ehdr, cursct)) == NULL) {
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98 goto quit;
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99 }
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100 }
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101
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102 if (cursct->sh_type == SHT_SYMTAB)
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103 symtab_found++;
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104
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105 if (cursct->sh_type == SHT_DYNSYM)
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106 dynsym_found++;
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107
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108 cursct++;
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109 }
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110
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111 if (!symtab_found && dynsym_found)
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112 symsection = SHT_DYNSYM;
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113
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114 for (cnt = 1; cnt < ehdr.e_shnum; cnt++) {
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115 ELF_SHDR *shdr = scn_cache[cnt].c_shdr;
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116
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117 if (shdr->sh_type == symsection) {
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118 ELF_SYM *syms;
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4006
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119 int j, n;
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3960
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120 size_t size;
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121
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122 // FIXME: there could be multiple data buffers associated with the
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123 // same ELF section. Here we can handle only one buffer. See man page
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124 // for elf_getdata on Solaris.
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125
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126 // guarantee(symtab == NULL, "multiple symtab");
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127 symtab = calloc(1, sizeof(*symtab));
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128 if (symtab == NULL) {
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129 goto quit;
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130 }
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131 // the symbol table
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132 syms = (ELF_SYM *)scn_cache[cnt].c_data;
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133
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134 // number of symbols
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135 n = shdr->sh_size / shdr->sh_entsize;
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136
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137 // create hash table, we use berkeley db to
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138 // manipulate the hash table.
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139 symtab->hash_table = dbopen(NULL, O_CREAT | O_RDWR, 0600, DB_HASH, NULL);
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140 // guarantee(symtab->hash_table, "unexpected failure: dbopen");
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4006
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141 if (symtab->hash_table == NULL)
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142 goto bad;
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3960
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143
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144 // shdr->sh_link points to the section that contains the actual strings
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145 // for symbol names. the st_name field in ELF_SYM is just the
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146 // string table index. we make a copy of the string table so the
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147 // strings will not be destroyed by elf_end.
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148 size = scn_cache[shdr->sh_link].c_shdr->sh_size;
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149 symtab->strs = malloc(size);
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4006
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150 if (symtab->strs == NULL)
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151 goto bad;
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3960
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152 memcpy(symtab->strs, scn_cache[shdr->sh_link].c_data, size);
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153
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154 // allocate memory for storing symbol offset and size;
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155 symtab->num_symbols = n;
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156 symtab->symbols = calloc(n , sizeof(*symtab->symbols));
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4006
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157 if (symtab->symbols == NULL)
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158 goto bad;
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3960
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159
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160 // copy symbols info our symtab and enter them info the hash table
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161 for (j = 0; j < n; j++, syms++) {
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162 DBT key, value;
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163 char *sym_name = symtab->strs + syms->st_name;
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164
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165 // skip non-object and non-function symbols
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166 int st_type = ELF_ST_TYPE(syms->st_info);
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167 if ( st_type != STT_FUNC && st_type != STT_OBJECT)
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168 continue;
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169 // skip empty strings and undefined symbols
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170 if (*sym_name == '\0' || syms->st_shndx == SHN_UNDEF) continue;
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171
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172 symtab->symbols[j].name = sym_name;
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173 symtab->symbols[j].offset = syms->st_value - baseaddr;
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174 symtab->symbols[j].size = syms->st_size;
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175
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176 key.data = sym_name;
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177 key.size = strlen(sym_name) + 1;
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178 value.data = &(symtab->symbols[j]);
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179 value.size = sizeof(void *);
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180 (*symtab->hash_table->put)(symtab->hash_table, &key, &value, 0);
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181 }
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182 }
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183 }
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4006
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184 goto quit;
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185
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186 bad:
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187 destroy_symtab(symtab);
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188 symtab = NULL;
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3960
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189
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190 quit:
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191 if (shbuf) free(shbuf);
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192 if (phbuf) free(phbuf);
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193 if (scn_cache) {
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194 for (cnt = 0; cnt < ehdr.e_shnum; cnt++) {
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195 if (scn_cache[cnt].c_data != NULL) {
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196 free(scn_cache[cnt].c_data);
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197 }
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198 }
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199 free(scn_cache);
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200 }
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201 return symtab;
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202 }
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203
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204 void destroy_symtab(struct symtab* symtab) {
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205 if (!symtab) return;
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206 if (symtab->strs) free(symtab->strs);
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207 if (symtab->symbols) free(symtab->symbols);
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208 if (symtab->hash_table) {
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4006
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209 (*symtab->hash_table->close)(symtab->hash_table);
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3960
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210 }
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211 free(symtab);
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212 }
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213
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214 uintptr_t search_symbol(struct symtab* symtab, uintptr_t base,
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215 const char *sym_name, int *sym_size) {
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216 DBT key, value;
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217 int ret;
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218
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219 // library does not have symbol table
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220 if (!symtab || !symtab->hash_table)
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221 return 0;
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222
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223 key.data = (char*)(uintptr_t)sym_name;
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224 key.size = strlen(sym_name) + 1;
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225 ret = (*symtab->hash_table->get)(symtab->hash_table, &key, &value, 0);
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226 if (ret == 0) {
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227 struct elf_symbol *sym = value.data;
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228 uintptr_t rslt = (uintptr_t) ((char*)base + sym->offset);
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229 if (sym_size) *sym_size = sym->size;
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230 return rslt;
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231 }
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232
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233 return 0;
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234 }
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235
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236 const char* nearest_symbol(struct symtab* symtab, uintptr_t offset,
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237 uintptr_t* poffset) {
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238 int n = 0;
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239 if (!symtab) return NULL;
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240 for (; n < symtab->num_symbols; n++) {
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4006
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241 struct elf_symbol* sym = &(symtab->symbols[n]);
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242 if (sym->name != NULL &&
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243 offset >= sym->offset && offset < sym->offset + sym->size) {
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244 if (poffset) *poffset = (offset - sym->offset);
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245 return sym->name;
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246 }
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3960
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247 }
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248 return NULL;
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249 }
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