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1 /* |
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2 checksum.c - implementation of the elf{32,64}_checksum(3) functions. |
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3 Copyright (C) 1995 - 2001 Michael Riepe |
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4 |
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5 This library is free software; you can redistribute it and/or |
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6 modify it under the terms of the GNU Library General Public |
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7 License as published by the Free Software Foundation; either |
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8 version 2 of the License, or (at your option) any later version. |
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9 |
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10 This library is distributed in the hope that it will be useful, |
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 Library General Public License for more details. |
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14 |
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15 You should have received a copy of the GNU Library General Public |
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16 License along with this library; if not, write to the Free Software |
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17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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18 */ |
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19 |
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20 #include <private.h> |
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21 |
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22 #ifndef lint |
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23 static const char rcsid[] = "@(#) $Id: checksum.c,v 1.6 2005/05/21 15:39:20 michael Exp $"; |
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24 #endif /* lint */ |
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25 |
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26 /* |
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27 * Compatibility note: |
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28 * |
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29 * The algorithm used in {elf32,elf64,gelf}_checksum() does not seem to |
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30 * be documented. I hope I got it right. My implementation does the |
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31 * following: |
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32 * |
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33 * - skip sections that do not have the SHF_ALLOC flag set |
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34 * - skip sections of type SHT_NULL, SHT_NOBITS, SHT_DYNSYM and |
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35 * SHT_DYNAMIC |
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36 * - add all data bytes from the remaining sections, modulo 2**32 |
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37 * - add upper and lower half of the result |
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38 * - subtract 0xffff if the result is > 0xffff |
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39 * - if any error occurs, return 0L |
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40 */ |
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41 |
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42 static int |
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43 skip_section(Elf_Scn *scn, unsigned cls) { |
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44 if (cls == ELFCLASS32) { |
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45 Elf32_Shdr *shdr = &scn->s_shdr32; |
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46 |
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47 if (!(shdr->sh_flags & SHF_ALLOC)) { |
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48 return 1; |
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49 } |
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50 switch (shdr->sh_type) { |
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51 case SHT_NULL: |
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52 case SHT_NOBITS: |
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53 /* Solaris seems to ignore these, too */ |
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54 case SHT_DYNSYM: |
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55 case SHT_DYNAMIC: |
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56 return 1; |
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57 } |
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58 } |
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59 #if __LIBELF64 |
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60 else if (cls == ELFCLASS64) { |
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61 Elf64_Shdr *shdr = &scn->s_shdr64; |
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62 |
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63 if (!(shdr->sh_flags & SHF_ALLOC)) { |
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64 return 1; |
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65 } |
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66 switch (shdr->sh_type) { |
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67 case SHT_NULL: |
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68 case SHT_NOBITS: |
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69 /* Solaris seems to ignore these, too */ |
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70 case SHT_DYNSYM: |
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71 case SHT_DYNAMIC: |
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72 return 1; |
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73 } |
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74 } |
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75 #endif /* __LIBELF64 */ |
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76 else { |
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77 seterr(ERROR_UNIMPLEMENTED); |
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78 } |
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79 return 0; |
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80 } |
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81 |
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82 static long |
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83 add_bytes(unsigned char *ptr, size_t len) { |
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84 long csum = 0; |
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85 |
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86 while (len--) { |
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87 csum += *ptr++; |
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88 } |
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89 return csum; |
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90 } |
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91 |
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92 static long |
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93 _elf_csum(Elf *elf) { |
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94 long csum = 0; |
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95 Elf_Data *data; |
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96 Elf_Scn *scn; |
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97 |
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98 if (!elf->e_ehdr && !_elf_cook(elf)) { |
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99 /* propagate errors from _elf_cook */ |
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100 return 0L; |
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101 } |
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102 seterr(0); |
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103 for (scn = elf->e_scn_1; scn; scn = scn->s_link) { |
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104 if (scn->s_index == SHN_UNDEF || skip_section(scn, elf->e_class)) { |
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105 continue; |
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106 } |
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107 data = NULL; |
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108 while ((data = elf_getdata(scn, data))) { |
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109 if (data->d_size) { |
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110 if (data->d_buf == NULL) { |
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111 seterr(ERROR_NULLBUF); |
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112 return 0L; |
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113 } |
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114 csum += add_bytes(data->d_buf, data->d_size); |
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115 } |
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116 } |
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117 } |
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118 if (_elf_errno) { |
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119 return 0L; |
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120 } |
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121 csum = (csum & 0xffff) + ((csum >> 16) & 0xffff); |
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122 if (csum > 0xffff) { |
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123 csum -= 0xffff; |
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124 } |
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125 return csum; |
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126 } |
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127 |
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128 long |
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129 elf32_checksum(Elf *elf) { |
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130 if (elf) { |
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131 if (elf->e_kind != ELF_K_ELF) { |
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132 seterr(ERROR_NOTELF); |
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133 } |
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134 else if (elf->e_class != ELFCLASS32) { |
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135 seterr(ERROR_CLASSMISMATCH); |
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136 } |
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137 else { |
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138 return _elf_csum(elf); |
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139 } |
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140 } |
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141 return 0L; |
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142 } |
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143 |
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144 #if __LIBELF64 |
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145 |
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146 long |
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147 elf64_checksum(Elf *elf) { |
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148 if (elf) { |
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149 if (elf->e_kind != ELF_K_ELF) { |
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150 seterr(ERROR_NOTELF); |
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151 } |
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152 else if (elf->e_class != ELFCLASS64) { |
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153 seterr(ERROR_CLASSMISMATCH); |
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154 } |
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155 else { |
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156 return _elf_csum(elf); |
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157 } |
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158 } |
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159 return 0L; |
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160 } |
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161 |
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162 long |
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163 gelf_checksum(Elf *elf) { |
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164 if (elf) { |
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165 if (elf->e_kind != ELF_K_ELF) { |
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166 seterr(ERROR_NOTELF); |
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167 } |
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168 else if (!valid_class(elf->e_class)) { |
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169 seterr(ERROR_UNKNOWN_CLASS); |
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170 } |
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171 else { |
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172 return _elf_csum(elf); |
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173 } |
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174 } |
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175 return 0L; |
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176 } |
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177 |
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178 #endif /* __LIBELF64 */ |