Ulrich Drepper | b08d5a8 | 2005-07-26 05:00:05 +0000 | [diff] [blame^] | 1 | <!doctype book PUBLIC "-//OASIS//DTD DocBook V4.1//EN"[ |
| 2 | <!ENTITY package "<filename>new-bu</filename>"> |
| 3 | ]> |
| 4 | |
| 5 | <book> |
| 6 | <title>New Binutils User's and Reference Manual</title> |
| 7 | |
| 8 | <chapter> |
| 9 | <title><filename>libelf</filename> <acronym>ABI</acronym></title> |
| 10 | |
| 11 | <simpara>The <acronym>ABI</acronym> of the |
| 12 | <filename>libelf</filename> implemented in the &package; package |
| 13 | is following that of Sun's implementation which in turn in derived |
| 14 | from the original SysVr4 implementation. There are some |
| 15 | extensions over Sun's versions, though, which makes it impossible |
| 16 | to replace this implementation with Sun's.</simpara> |
| 17 | |
| 18 | <beginpage> |
| 19 | |
| 20 | <refentry xreflabel="Elf_Data" id="ElfUData"> |
| 21 | <refnamediv> |
| 22 | <refname>Elf_Data</refname> |
| 23 | <refpurpose>Descriptor for Data Buffer</refpurpose> |
| 24 | </refnamediv> |
| 25 | |
| 26 | <refsynopsisdiv> |
| 27 | <synopsis> |
| 28 | #include <libelf.h> |
| 29 | </synopsis> |
| 30 | </refsynopsisdiv> |
| 31 | |
| 32 | <refsect1> |
| 33 | <title>Description</title> |
| 34 | |
| 35 | <simpara>The <structname>Elf_Data</structname> structure is as |
| 36 | a descriptor for a data buffer associated with a section. |
| 37 | Every data buffer is associated with a specific section (see |
| 38 | <!-- xref --><structname>Elf_Scn</structname>).</simpara> |
| 39 | |
| 40 | <simpara>A data buffer is created when reading a file. In |
| 41 | this case only a single buffer is present in the section. The |
| 42 | user can add as many sections as wanted to a section and they |
| 43 | can be retrieved using the <function>elf_getdata</function> |
| 44 | and <function>elf_rawdata</function> functions.<!-- xref |
| 45 | --></simpara> |
| 46 | |
| 47 | <simpara>The <structname>Elf_Data</structname> structure |
| 48 | contains the following members:</simpara> |
| 49 | |
| 50 | <programlisting> |
| 51 | void *d_buf |
| 52 | Elf_Type d_type |
| 53 | size_t d_size |
| 54 | off_t d_off |
| 55 | size_t d_align |
| 56 | unsigned int d_version |
| 57 | </programlisting> |
| 58 | |
| 59 | <simpara>All of these members can be modified directly by the |
| 60 | user. They can be used to resize a section, to change its |
| 61 | content or type, and many more tasks. This is also true for |
| 62 | the data read from a file. The meaning of each member is as |
| 63 | follows:</simpara> |
| 64 | |
| 65 | <variablelist> |
| 66 | <varlistentry> |
| 67 | <term><structfield>d_buf</structfield></term> |
| 68 | <listitem> |
| 69 | <simpara>The <structfield>d_buf</structfield> member is |
| 70 | the pointer to the buffer with the actual data. When |
| 71 | the ELF file was read from a file the first and only |
| 72 | data buffer of a section is allocated by the |
| 73 | <filename>libelf</filename> library. The user should |
| 74 | not try to resize or free this buffer. When the user |
| 75 | adds a new data buffer to a section the associated |
| 76 | memory block is normally allocated by the user. It is |
| 77 | important that the buffer must have a lifetime at least |
| 78 | until the ELF file is closed entirely (important when |
| 79 | the buffer is allocated on the stack). If the buffer is |
| 80 | not allocated on the stack it is the user's |
| 81 | responsibility to free the buffer after it is not used |
| 82 | anymore. The <structfield>d_buf</structfield> member |
| 83 | can contain a null pointer if the data buffer is |
| 84 | empty.</simpara> |
| 85 | </listitem> |
| 86 | </varlistentry> |
| 87 | |
| 88 | <varlistentry> |
| 89 | <term><structfield>d_type</structfield></term> |
| 90 | <listitem> |
| 91 | <simpara>The <structfield>d_type</structfield> |
| 92 | determines how the data of the buffer is interpreted. |
| 93 | This type is determined from the section type and must |
| 94 | be the same for all data buffers for a section. See |
| 95 | <!-- xref --><type>Elf_Type</type> for more information. |
| 96 | The <function><link linkend="elfUgetdata" |
| 97 | endterm="elfUgetdata.refname"></link></function> |
| 98 | function uses this information to convert the data of |
| 99 | the buffer between the external form and the form |
| 100 | represented to the user and back if necessary.</simpara> |
| 101 | </listitem> |
| 102 | </varlistentry> |
| 103 | |
| 104 | <varlistentry> |
| 105 | <term><structfield>d_version</structfield></term> |
| 106 | <listitem> |
| 107 | <simpara>The <structfield>d_version</structfield> |
| 108 | contains the ELF version of the file.</simpara> |
| 109 | </listitem> |
| 110 | </varlistentry> |
| 111 | |
| 112 | <varlistentry> |
| 113 | <term><structfield>d_size</structfield></term> |
| 114 | <listitem> |
| 115 | <simpara>The <structfield>d_size</structfield> contains |
| 116 | the size of the buffer in bytes.</simpara> |
| 117 | </listitem> |
| 118 | </varlistentry> |
| 119 | |
| 120 | <varlistentry> |
| 121 | <term><structfield>d_off</structfield></term> |
| 122 | <listitem> |
| 123 | <simpara>The <structfield>d_off</structfield> is the |
| 124 | offset into the section in bytes.</simpara> |
| 125 | </listitem> |
| 126 | </varlistentry> |
| 127 | |
| 128 | <varlistentry> |
| 129 | <term><structfield>d_align</structfield></term> |
| 130 | <listitem> |
| 131 | <simpara>The <structfield>d_align</structfield> is the |
| 132 | address alignment of the section in bytes.</simpara> |
| 133 | </listitem> |
| 134 | </varlistentry> |
| 135 | </variablelist> |
| 136 | </refsect1> |
| 137 | </refentry> |
| 138 | |
| 139 | <beginpage> |
| 140 | |
| 141 | <refentry id="elfUgetdata"> |
| 142 | <refnamediv> |
| 143 | <refname id="elfUgetdata.refname">elf_getdata</refname> |
| 144 | <refpurpose>Get washed data of section</refpurpose> |
| 145 | </refnamediv> |
| 146 | |
| 147 | <refsynopsisdiv> |
| 148 | <funcsynopsis> |
| 149 | <funcsynopsisinfo> |
| 150 | #include <libelf.h> |
| 151 | </funcsynopsisinfo> |
| 152 | <funcprototype> |
| 153 | <funcdef>Elf_Data *<function>elf_getdata</function></funcdef> |
| 154 | <paramdef>Elf_Scn *<parameter>scn</parameter></paramdef> |
| 155 | <paramdef>Elf_Data *<parameter>data</parameter></paramdef> |
| 156 | </funcprototype> |
| 157 | </funcsynopsis> |
| 158 | </refsynopsisdiv> |
| 159 | |
| 160 | <refsect1> |
| 161 | <title>Description</title> |
| 162 | |
| 163 | <simpara>The <function>elf_getdata</function> function allows |
| 164 | the user to retrieve the data buffers of the section |
| 165 | <parameter>scn</parameter>. There can be more than one buffer |
| 166 | if the user explicitly added them. When a file is read the |
| 167 | <filename>libelf</filename> library creates exactly one data |
| 168 | buffer.</simpara> |
| 169 | |
| 170 | <simpara>The first buffer in the list can be obtained by |
| 171 | passing a null pointer in the parameter |
| 172 | <parameter>data</parameter>. To get the next data buffer the |
| 173 | previously returned value must be passed in the |
| 174 | <parameter>data</parameter> parameter. If there are no more |
| 175 | buffer left in the list a null pointer is returned.</simpara> |
| 176 | |
| 177 | <simpara>If the <parameter>data</parameter> parameter is not a |
| 178 | null pointer it must be a descriptor for a buffer |
| 179 | associated with the section <parameter>scn</parameter>. If |
| 180 | this is not the case a null pointer is returned. To |
| 181 | facilitate error handling <function>elf_getdata</function> |
| 182 | also returns a null pointer if the <parameter>scn</parameter> |
| 183 | parameter is a null pointer.</simpara> |
| 184 | </refsect1> |
| 185 | </refentry> |
| 186 | |
| 187 | <refentry> |
| 188 | <refnamediv> |
| 189 | <refname id="elfUupdate.refname">elf_update</refname> |
| 190 | <refpurpose>update an ELF descriptor</refpurpose> |
| 191 | </refnamediv> |
| 192 | |
| 193 | <refsynopsisdiv> |
| 194 | <funcsynopsis> |
| 195 | <funcsynopsisinfo> |
| 196 | #include <libelf.h> |
| 197 | </funcsynopsisinfo> |
| 198 | <funcprototype> |
| 199 | <funcdef>off_t <function>elf_update</function></funcdef> |
| 200 | <paramdef>Elf *<parameter>elf</parameter></paramdef> |
| 201 | <paramdef>Elf_Cmd <parameter>cmd</parameter></paramdef> |
| 202 | </funcprototype> |
| 203 | </funcsynopsis> |
| 204 | </refsynopsisdiv> |
| 205 | |
| 206 | <refsect1> |
| 207 | <title>Description</title> |
| 208 | |
| 209 | <simpara>The user is responsible for filling in the following |
| 210 | fields in the named data structures:</simpara> |
| 211 | |
| 212 | <table> |
| 213 | <title>Fields not set by <function>elf_update</function></title> |
| 214 | <tgroup cols="3"> |
| 215 | <colspec colwidth="90pt"> |
| 216 | <colspec colwidth="110pt"> |
| 217 | <thead> |
| 218 | <row> |
| 219 | <entry>Data Structure</entry> |
| 220 | <entry>Member</entry> |
| 221 | <entry>Exception</entry> |
| 222 | </row> |
| 223 | </thead> |
| 224 | <tbody> |
| 225 | <row> |
| 226 | <entry morerows="8"><type>Elfxx_Ehdr</type></entry> |
| 227 | <entry>e_ident[EI_DATA]</entry> |
| 228 | <entry>see below</entry> |
| 229 | </row> |
| 230 | <row> |
| 231 | <entry></entry> |
| 232 | <entry>e_type</entry> |
| 233 | <!-- <entry morerows="1"></entry> --> |
| 234 | <entry></entry> |
| 235 | </row> |
| 236 | <row> |
| 237 | <entry></entry> |
| 238 | <entry>e_machine</entry> |
| 239 | <entry></entry> |
| 240 | </row> |
| 241 | <row> |
| 242 | <entry></entry> |
| 243 | <entry>e_version</entry> |
| 244 | <entry>see below</entry> |
| 245 | </row> |
| 246 | <row> |
| 247 | <entry></entry> |
| 248 | <entry>e_entry</entry> |
| 249 | <entry></entry> |
| 250 | </row> |
| 251 | <row> |
| 252 | <entry></entry> |
| 253 | <entry>e_phoff</entry> |
| 254 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 255 | </row> |
| 256 | <row> |
| 257 | <entry></entry> |
| 258 | <entry>e_shoff</entry> |
| 259 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 260 | </row> |
| 261 | <row> |
| 262 | <entry></entry> |
| 263 | <entry>e_flags</entry> |
| 264 | <entry></entry> |
| 265 | </row> |
| 266 | <row> |
| 267 | <entry></entry> |
| 268 | <entry>e_shstrndx</entry> |
| 269 | <entry></entry> |
| 270 | </row> |
| 271 | <row> |
| 272 | <entry morerows="7">Elfxx_Phdr</entry> |
| 273 | <entry>p_type</entry> |
| 274 | <entry morerows="7"></entry> |
| 275 | </row> |
| 276 | <row> |
| 277 | <entry></entry> |
| 278 | <entry>p_offset</entry> |
| 279 | <entry></entry> |
| 280 | </row> |
| 281 | <row> |
| 282 | <entry></entry> |
| 283 | <entry>p_vaddr</entry> |
| 284 | <entry></entry> |
| 285 | </row> |
| 286 | <row> |
| 287 | <entry></entry> |
| 288 | <entry>p_paddr</entry> |
| 289 | <entry></entry> |
| 290 | </row> |
| 291 | <row> |
| 292 | <entry></entry> |
| 293 | <entry>p_filesz</entry> |
| 294 | <entry></entry> |
| 295 | </row> |
| 296 | <row> |
| 297 | <entry></entry> |
| 298 | <entry>p_memsz</entry> |
| 299 | <entry></entry> |
| 300 | </row> |
| 301 | <row> |
| 302 | <entry></entry> |
| 303 | <entry>p_flags</entry> |
| 304 | <entry></entry> |
| 305 | </row> |
| 306 | <row> |
| 307 | <entry></entry> |
| 308 | <entry>p_align</entry> |
| 309 | <entry></entry> |
| 310 | </row> |
| 311 | |
| 312 | <row> |
| 313 | <entry morerows="9">Elfxx_Shdr</entry> |
| 314 | <entry>sh_name</entry> |
| 315 | <entry morerows="3"></entry> |
| 316 | </row> |
| 317 | <row> |
| 318 | <entry></entry> |
| 319 | <entry>sh_type</entry> |
| 320 | <entry></entry> |
| 321 | </row> |
| 322 | <row> |
| 323 | <entry></entry> |
| 324 | <entry>sh_flags</entry> |
| 325 | <entry></entry> |
| 326 | </row> |
| 327 | <row> |
| 328 | <entry></entry> |
| 329 | <entry>sh_addr</entry> |
| 330 | <entry></entry> |
| 331 | </row> |
| 332 | <row> |
| 333 | <entry></entry> |
| 334 | <entry>sh_offset</entry> |
| 335 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 336 | </row> |
| 337 | <row> |
| 338 | <entry></entry> |
| 339 | <entry>sh_size</entry> |
| 340 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 341 | </row> |
| 342 | <row> |
| 343 | <entry></entry> |
| 344 | <entry>sh_link</entry> |
| 345 | <!-- <entry morerows="1"></entry> --> |
| 346 | <entry></entry> |
| 347 | </row> |
| 348 | <row> |
| 349 | <entry></entry> |
| 350 | <entry>sh_info</entry> |
| 351 | <entry></entry> |
| 352 | </row> |
| 353 | <row> |
| 354 | <entry></entry> |
| 355 | <entry>sh_addralign</entry> |
| 356 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 357 | </row> |
| 358 | <row> |
| 359 | <entry></entry> |
| 360 | <entry>sh_entsize</entry> |
| 361 | <entry></entry> |
| 362 | </row> |
| 363 | |
| 364 | <row> |
| 365 | <entry morerows="5">Elf_Data</entry> |
| 366 | <entry>d_buf</entry> |
| 367 | <entry morerows="2"></entry> |
| 368 | </row> |
| 369 | <row> |
| 370 | <entry></entry> |
| 371 | <entry>d_type</entry> |
| 372 | <entry></entry> |
| 373 | </row> |
| 374 | <row> |
| 375 | <entry></entry> |
| 376 | <entry>d_size</entry> |
| 377 | <entry></entry> |
| 378 | </row> |
| 379 | <row> |
| 380 | <entry></entry> |
| 381 | <entry>d_off</entry> |
| 382 | <entry>if <symbol>ELF_F_LAYOUT</symbol> is used</entry> |
| 383 | </row> |
| 384 | <row> |
| 385 | <entry></entry> |
| 386 | <entry>d_align</entry> |
| 387 | <!-- <entry morerows="1"></entry> --> |
| 388 | <entry></entry> |
| 389 | </row> |
| 390 | <row> |
| 391 | <entry></entry> |
| 392 | <entry>d_version</entry> |
| 393 | <entry></entry> |
| 394 | </row> |
| 395 | </tbody> |
| 396 | </tgroup> |
| 397 | </table> |
| 398 | |
| 399 | <simpara>Two fields of the ELF header are handled in a special |
| 400 | way:</simpara> |
| 401 | |
| 402 | <variablelist> |
| 403 | <varlistentry> |
| 404 | <term>e_version</term> |
| 405 | <listitem> |
| 406 | <simpara>The user can set this field to the vvalue for |
| 407 | the version to be used. It is an error if the library |
| 408 | cannot handle this version. If the field contains the |
| 409 | value <symbol>EV_NONE</symbol> the library will fill in |
| 410 | its own internal version.</simpara> |
| 411 | </listitem> |
| 412 | </varlistentry> |
| 413 | |
| 414 | <varlistentry> |
| 415 | <term>e_ident[EI_DATA]</term> |
| 416 | <listitem> |
| 417 | <simpara>The user should fill in the byte ordering for |
| 418 | the file. If the value of the field is |
| 419 | <symbol>ELFDATANONE</symbol> the library replaces it |
| 420 | with the native byte ordering for the machine.</simpara> |
| 421 | </listitem> |
| 422 | </varlistentry> |
| 423 | </variablelist> |
| 424 | </refsect1> |
| 425 | </refentry> |
| 426 | </chapter> |
| 427 | |
| 428 | <chapter> |
| 429 | <title><filename>libelf</filename> Internals</title> |
| 430 | |
| 431 | <simpara>Since the binary format handling tools need constant |
| 432 | attention since there are always new machines and varients |
| 433 | therefore coming out it is important to have the implementation |
| 434 | well documented. Only this way extensions can be made in the |
| 435 | right places and the mistakes of the past avoided.</simpara> |
| 436 | </chapter> |
| 437 | </book> |
| 438 | <!-- Keep this comment at the end of the file |
| 439 | Local variables: |
| 440 | mode: sgml |
| 441 | sgml-omitag:nil |
| 442 | sgml-shorttag:t |
| 443 | End: |
| 444 | --> |