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4 | .\" modification, are permitted provided that the following conditions |
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9 | .\" notice, this list of conditions and the following disclaimer in the |
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12 | .\" This software is provided by Joseph Koshy ``as is'' and |
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24 | .\" $Id: elf_getdata.3 1766 2011-08-22 06:01:03Z jkoshy $ |
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25 | .\" |
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26 | .Dd January 26, 2011 |
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27 | .Os |
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28 | .Dt ELF_GETDATA 3 |
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29 | .Sh NAME |
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30 | .Nm elf_getdata , |
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31 | .Nm elf_newdata , |
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32 | .Nm elf_rawdata |
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33 | .Nd iterate through or allocate section data |
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34 | .Sh LIBRARY |
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35 | .Lb libelf |
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36 | .Sh SYNOPSIS |
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37 | .In libelf.h |
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38 | .Ft "Elf_Data *" |
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39 | .Fn elf_getdata "Elf_Scn *scn" "Elf_Data *data" |
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40 | .Ft "Elf_Data *" |
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41 | .Fn elf_newdata "Elf_Scn *scn" |
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42 | .Ft "Elf_Data *" |
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43 | .Fn elf_rawdata "Elf_Scn *scn" "Elf_Data *data" |
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44 | .Sh DESCRIPTION |
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45 | These functions are used to access and manipulate data descriptors |
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46 | associated with section descriptors. |
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47 | Data descriptors used by the ELF library are described in |
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48 | .Xr elf 3 . |
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49 | .Pp |
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50 | Function |
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51 | .Fn elf_getdata |
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52 | will return the next data descriptor associated with section descriptor |
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53 | .Ar scn . |
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54 | The returned data descriptor will be setup to contain translated data. |
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55 | Argument |
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56 | .Ar data |
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57 | may be NULL, in which case the function returns the first data descriptor |
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58 | associated with section |
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59 | .Ar scn . |
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60 | If argument |
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61 | .Ar data |
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62 | is not NULL, it must be a pointer to a data descriptor associated with |
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63 | section descriptor |
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64 | .Ar scn , |
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65 | and function |
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66 | .Fn elf_getdata |
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67 | will return a pointer to the next data descriptor for the section, |
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68 | or NULL when the end of the section's descriptor list is reached. |
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69 | .Pp |
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70 | Function |
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71 | .Fn elf_newdata |
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72 | will allocate a new data descriptor and append it to the list of data |
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73 | descriptors associated with section descriptor |
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74 | .Ar scn . |
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75 | The new data descriptor will be initialized as follows: |
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76 | .Bl -tag -width "d_version" -compact -offset indent |
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77 | .It Va d_align |
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78 | Set to 1. |
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79 | .It Va d_buf |
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80 | Initialized to NULL. |
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81 | .It Va d_off |
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82 | Set to (off_t) -1. |
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83 | This field is under application control if the |
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84 | .Dv ELF_F_LAYOUT |
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85 | flag was set on the ELF descriptor. |
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86 | .It Va d_size |
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87 | Set to zero. |
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88 | .It Va d_type |
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89 | Initialized to |
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90 | .Dv ELF_T_BYTE . |
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91 | .It Va d_version |
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92 | Set to the current working version of the library, as set by |
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93 | .Xr elf_version 3 . |
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94 | .El |
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95 | The application must set these values as appropriate before |
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96 | calling |
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97 | .Xr elf_update 3 . |
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98 | Section |
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99 | .Ar scn |
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100 | must be associated with an ELF file opened for writing. |
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101 | If the application has not requested full control of layout by |
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102 | setting the |
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103 | .Dv ELF_F_LAYOUT |
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104 | flag on descriptor |
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105 | .Ar elf , |
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106 | then the data referenced by the returned descriptor will be positioned |
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107 | after the existing content of the section, honoring the file alignment |
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108 | specified in member |
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109 | .Va d_align . |
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110 | On successful completion of a call to |
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111 | .Fn elf_newdata , |
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112 | the ELF library will mark the section |
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113 | .Ar scn |
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114 | as |
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115 | .Dq dirty . |
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116 | .Pp |
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117 | Function |
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118 | .Fn elf_rawdata |
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119 | is used to step through the data descriptors associated with |
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120 | section |
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121 | .Ar scn . |
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122 | In contrast to function |
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123 | .Fn elf_getdata , |
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124 | this function returns untranslated data. |
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125 | If argument |
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126 | .Ar data |
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127 | is NULL, the first data descriptor associated with section |
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128 | .Ar scn |
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129 | is returned. |
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130 | If argument |
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131 | .Ar data |
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132 | is not NULL, is must be a data descriptor associated with |
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133 | section |
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134 | .Ar scn , |
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135 | and function |
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136 | .Fn elf_rawdata |
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137 | will return the next data descriptor in the list, or NULL |
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138 | if no further descriptors are present. |
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139 | Function |
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140 | .Fn elf_rawdata |
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141 | always returns |
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142 | .Vt Elf_Data |
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143 | structures of type |
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144 | .Dv ELF_T_BYTE . |
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145 | .Ss Special handling of zero-sized and SHT_NOBITS sections |
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146 | For sections of type |
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147 | .Dv SHT_NOBITS, |
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148 | and for zero-sized sections, |
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149 | the functions |
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150 | .Fn elf_getdata |
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151 | and |
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152 | .Fn elf_rawdata |
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153 | return a pointer to a valid |
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154 | .Vt Elf_Data |
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155 | structure that has its |
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156 | .Va d_buf |
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157 | member set to NULL and its |
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158 | .Va d_size |
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159 | member set to the size of the section. |
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160 | .Pp |
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161 | If an application wishes to create a section of type |
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162 | .Dv SHT_NOBITS , |
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163 | it should add a data buffer to the section using function |
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164 | .Fn elf_newdata . |
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165 | It should then set the |
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166 | .Va d_buf |
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167 | and |
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168 | .Va d_size |
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169 | members of the returned |
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170 | .Vt Elf_Data |
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171 | structure to NULL and the desired size of the section respectively. |
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172 | .Sh RETURN VALUES |
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173 | These functions return a valid pointer to a data descriptor if successful, or |
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174 | NULL if an error occurs. |
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175 | .Sh ERRORS |
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176 | These functions may fail with the following errors: |
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177 | .Bl -tag -width "[ELF_E_RESOURCE]" |
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178 | .It Bq Er ELF_E_ARGUMENT |
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179 | Either of the arguments |
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180 | .Ar scn |
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181 | or |
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182 | .Ar data |
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183 | was NULL. |
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184 | .It Bq Er ELF_E_ARGUMENT |
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185 | The data descriptor referenced by argument |
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186 | .Ar data |
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187 | is not associated with section descriptor |
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188 | .Ar scn . |
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189 | .It Bq Er ELF_E_ARGUMENT |
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190 | The section denoted by argument |
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191 | .Ar scn |
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192 | had no data associated with it. |
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193 | .It Bq Er ELF_E_DATA |
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194 | Retrieval of data from the underlying object failed. |
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195 | .It Bq Er ELF_E_RESOURCE |
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196 | An out of memory condition was detected. |
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197 | .It Bq Er ELF_E_SECTION |
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198 | Section |
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199 | .Ar scn |
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200 | had type |
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201 | .Dv SHT_NULL . |
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202 | .It Bq Er ELF_E_SECTION |
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203 | The type of the section |
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204 | .Ar scn |
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205 | was not recognized by the library. |
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206 | .It Bq Er ELF_E_SECTION |
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207 | The size of the section |
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208 | .Ar scn |
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209 | is not a multiple of the file size for its section type. |
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210 | .It Bq Er ELF_E_SECTION |
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211 | The file offset for section |
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212 | .Ar scn |
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213 | is incorrect. |
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214 | .It Bq Er ELF_E_UNIMPL |
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215 | The section type associated with section |
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216 | .Ar scn |
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217 | is currently unsupported by the library. |
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218 | .El |
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219 | .Sh SEE ALSO |
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220 | .Xr elf 3 , |
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221 | .Xr elf_flagdata 3 , |
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222 | .Xr elf_flagscn 3 , |
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223 | .Xr elf_getscn 3 , |
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224 | .Xr elf_getshdr 3 , |
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225 | .Xr elf_newscn 3 , |
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226 | .Xr elf_rawfile 3 , |
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227 | .Xr elf_update 3 , |
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228 | .Xr elf_version 3 , |
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229 | .Xr gelf 3 |
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