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31 .Nd API for manipulating ELF objects
39 library provides functions that allow an application to read and
40 manipulate ELF object files, and to read
43 The library allows the manipulation of ELF objects in a byte ordering
44 and word-size independent way, allowing an application to read and
45 create ELF objects for 32 and 64 bit architectures and for little-
46 and big-endian machines.
47 The library is capable of processing ELF objects that use extended
50 This manual page serves to provide an overview of the functionality in
52 Further information may found in the manual pages for individual
54 functions that comprise the library.
58 ELF files contain several data structures that are laid out in a
60 ELF files begin with an
61 .Dq Executable Header ,
62 and may contain an optional
63 .Dq Program Header Table ,
64 and optional data in the form of ELF
67 .Dq Section Header Table
68 describes the content of the data in these sections.
70 ELF objects have an associated
72 which denotes the natural machine word size for the architecture
73 the object is associated with.
74 Objects for 32 bit architectures have an ELF class of
76 Objects for 64 bit architectures have an ELF class of
79 ELF objects also have an associated
81 which denotes the endianness of the machine architecture associated
85 for little-endian architectures and
87 for big-endian architectures.
89 ELF objects are also associated with an API version number.
90 This version number determines the layout of the individual components
91 of an ELF file and the semantics associated with these.
92 .Ss Data Representation And Translation
95 library distinguishes between
97 representations of ELF data structures and their
101 An application would work with ELF data in its
103 representation, i.e., using the native byteorder and alignment mandated
104 by the processor the application is running on.
107 representation of the same data could use a different byte ordering
108 and follow different constraints on object alignment than these native
113 library offers translation facilities
114 .Xr ( elf32_xlatetof 3 ,
115 .Xr elf32_xlatetom 3 ,
118 .Xr elf64_xlatetom 3 )
120 representations and also provides higher-level APIs that retrieve and store
121 data from the ELF object in a transparent manner.
122 .Ss Library Working Version
123 Conceptually, there are three version numbers associated with an
124 application using the ELF library to manipulate ELF objects:
125 .Bl -bullet -compact -offset indent
127 The ELF version that the application was compiled against.
128 This version determines the ABI expected by the application.
130 The ELF version of the ELF object being manipulated by the
131 application through the ELF library.
133 The ELF version (or set of versions) supported by the ELF library itself.
136 In order to facilitate working with ELF objects of differing versions,
137 the ELF library requires the application to call the
139 function before invoking many of its operations, in order to inform
140 the library of the application's desired working version.
142 In the current implementation, all three versions have to be
145 The ELF library uses the following prefixes:
146 .Bl -tag -width "ELF_F_*"
148 Used for class-independent functions.
150 Used for functions working with 32 bit ELF objects.
152 Used for functions working with 64 bit ELF objects.
154 Used for class-independent data types.
156 Used for command values used in a few functions.
157 These symbols are defined as members of the
161 Used for error numbers.
165 These constants define the kind of file associated with an ELF
169 The symbols are defined by the
173 These values are defined by the
175 enumeration, and denote the types of ELF data structures
176 that can be present in an ELF object.
179 Applications communicate with the library using descriptors.
181 .Bl -tag -width ".Vt Elf_Data"
185 descriptor represents an ELF object or an
188 It is allocated using one of the
195 descriptor can be used to read and write data to an ELF file.
198 descriptor can be associated with zero or more
202 Given an ELF descriptor, the application may retrieve the ELF
203 object's class-dependent
204 .Dq "Executable Header"
210 A new Ehdr structure may be allocated using the
217 .Dq "Program Header Table"
218 associated with an ELF descriptor may be allocated using the
223 A new program header table may be allocated or an existing table
232 structure is opaque and has no members visible to the
234 .\" TODO describe the Elf_Arhdr and Elf_Arsym structures.
238 data structure describes an individual chunk of a ELF file as
239 represented in memory.
240 It has the following application visible members:
241 .Bl -tag -width ".Vt unsigned int d_version" -compact
242 .It Vt "uint64_t d_align"
243 The in-file alignment of the data buffer within its containing ELF section.
244 This value must be a power of two.
245 .It Vt "uint64_t d_off"
246 The offset with the containing section where this descriptors data
248 This field will be computed by the library unless the application
249 requests full control of the ELF object's layout.
250 .It Vt "uint64_t d_size"
251 The number of bytes of data in this descriptor.
253 A pointer to data in memory.
254 .It Vt "Elf_Type d_type"
255 The ELF type (see below) of the data in this descriptor.
256 .It Vt "unsigned int d_version"
257 The operating version for the data in this buffer.
261 descriptors are usually associated with
264 Existing data descriptors associated with an ELF section may be
265 structures are retrieved using the
270 function may be used to attach new data descriptors to an ELF section.
273 descriptors represent a section in an ELF object.
275 They are retrieved using the
278 An application may iterate through the existing sections of an ELF
282 New sections may be allocated using the
288 descriptor is opaque and contains no application modifiable fields.
290 .Ss Supported Elf Types
291 The following ELF datatypes are supported by the library.
293 .Bl -tag -width ".Dv ELF_T_SYMINFO" -compact
298 The library will not attempt to translate byte data.
300 Software and hardware capability records.
302 Records used in a section of type
305 ELF executable header.
307 16-bit unsigned words.
309 64 bit unsigned words.
312 .\".It Dv ELF_T_MOVEP
313 .\" As yet unsupported.
319 ELF program header table entries.
321 ELF relocation entries.
323 ELF relocation entries with addends.
325 ELF section header entries.
331 ELF symbol information.
333 ELF symbol table entries.
335 Symbol version definition records.
337 Symbol version requirement records.
339 Unsigned 32-bit words.
341 Unsigned 64-bit words.
346 denotes the number of Elf types known to the library.
348 The following table shows the mapping between ELF section types
351 and the types supported by the library.
352 .Bl -column ".Dv SHT_PREINIT_ARRAY" ".Dv ELF_T_SYMINFO"
353 .It Em Section Type Ta Em "Library Type" Ta Em Description
354 .It Dv SHT_DYNAMIC Ta Dv ELF_T_DYN Ta Xo
358 .It Dv SHT_DYNSYM Ta Dv ELF_T_SYM Ta Symbols for dynamic linking.
359 .It Dv SHT_FINI_ARRAY Ta Dv ELF_T_ADDR Ta Termination function pointers.
360 .It Dv SHT_GROUP Ta Dv ELF_T_WORD Ta Section group marker.
361 .It Dv SHT_HASH Ta Dv ELF_T_HASH Ta Symbol hashes.
362 .It Dv SHT_INIT_ARRAY Ta Dv ELF_T_ADDR Ta Initialization function pointers.
363 .It Dv SHT_NOBITS Ta Dv ELF_T_BYTE Ta Xo
368 .It Dv SHT_NOTE Ta Dv ELF_T_NOTE Ta ELF note records.
369 .It Dv SHT_PREINIT_ARRAY Ta Dv ELF_T_ADDR Ta Pre-initialization function pointers.
370 .It Dv SHT_PROGBITS Ta Dv ELF_T_BYTE Ta Machine code.
371 .It Dv SHT_REL Ta Dv ELF_T_REL Ta ELF relocation records.
372 .It Dv SHT_RELA Ta Dv ELF_T_RELA Ta Relocation records with addends.
373 .It Dv SHT_STRTAB Ta Dv ELF_T_BYTE Ta String tables.
374 .It Dv SHT_SYMTAB Ta Dv ELF_T_SYM Ta Symbol tables.
375 .It Dv SHT_SYMTAB_SHNDX Ta Dv ELF_T_WORD Ta Used with extended section numbering.
376 .It Dv SHT_GNU_verdef Ta Dv ELF_T_VDEF Ta Symbol version definitions.
377 .It Dv SHT_GNU_verneed Ta Dv ELF_T_VNEED Ta Symbol versioning requirements.
378 .It Dv SHT_GNU_versym Ta Dv ELF_T_HALF Ta Version symbols.
379 .It Dv SHT_SUNW_move Ta Dv ELF_T_MOVE Ta ELF move records.
380 .It Dv SHT_SUNW_syminfo Ta Dv ELF_T_SYMINFO Ta Additional symbol flags.
383 .Ss Functional Grouping
384 This section contains a brief overview of the available functionality
386 Each function listed here is described further in its own manual page.
387 .Bl -tag -width indent
391 Retrieve the archive symbol table.
393 Retrieve the archive header for an object.
395 Retrieve the offset of a member inside an archive.
401 Random access inside an
405 .It "Data Structures"
408 Retrieve translated data for an ELF section.
410 Retrieve the section descriptor for a named section.
412 Retrieve the index for a section.
416 descriptor to an ELF section.
418 Add a new section descriptor to an ELF descriptor.
420 Iterate through the sections in an ELF object.
422 Retrieve untranslated data for an ELF sectino.
424 Return a pointer to the untranslated file contents for an ELF object.
425 .It Fn elf32_getehdr , Fn elf64_getehdr
426 Retrieve the Executable Header in an ELF object.
427 .It Fn elf32_getphdr , Fn elf64_getphdr
428 Retrieve the Program Header Table in an ELF object.
429 .It Fn elf32_getshdr , Fn elf64_getshdr
430 Retrieve the ELF section header associated with an
433 .It Fn elf32_newehdr , Fn elf64_newehdr
434 Allocate an Executable Header in an ELF object.
435 .It Fn elf32_newphdr , Fn elf64_newphdr
436 Allocate or resize the Program Header Table in an ELF object.
438 .It "Data Translation"
440 .It Fn elf32_xlatetof , Fn elf64_xlatetof
441 Translate an ELF data structure from its native representation to its
443 .It Fn elf32_xlatetom , Fn elf64_xlatetom
444 Translate an ELF data structure from its file representation to a
445 native representation.
447 .It "Error Reporting"
450 Retrieve the current error.
452 Retrieve a human readable description of the current error.
459 archive or ELF object given a file descriptor.
461 Close an ELF descriptor and release all its resources.
465 archive or ELF object present in a memory arena.
467 Sets the operating version.
470 .Bl -tag -width ".Fn elf_setshstrndx" -compact
472 Manage the association between and ELF descriptor and its underlying file.
478 Mark the ELF Executable Header in an ELF descriptor as dirty.
480 Mark the ELF Program Header Table in an ELF descriptor as dirty.
486 Mark an ELF Section Header as dirty.
487 .It Fn elf_setshstrndx
488 Set the index of the section name string table for the ELF object.
490 Recompute ELF object layout and optionally write the modified object
491 back to the underlying file.
494 .Bl -tag -width ".Fn elf_getshstrndx" -compact
495 .It Fn elf32_checksum , Fn elf64_checkum
496 Compute checksum of an ELF object.
498 Retrieve the identification bytes for an ELF object.
500 Retrieve the number of sections in an ELF object.
501 .It Fn elf_getshstrndx
502 Retrieve the section index of the section name string table in
505 Compute the ELF hash value of a string.
507 Query the kind of object associated with an ELF descriptor.
508 .It Fn elf32_fsize , Fn elf64_fsize
509 Return the size of the file representation of an ELF type.
512 .Ss Controlling ELF Object Layout
513 In the usual mode of operation, library will compute section
514 offsets and alignments based on the contents of an ELF descriptor's
515 sections without need for further intervention by the
518 However, if the application wishes to take complete charge of the
519 layout of the ELF file, it may set the
521 flag on an ELF descriptor using
523 following which the library will use the data offsets and alignments
524 specified by the application when laying out the file.
526 Gaps in between sections will be filled with the fill character
530 In case an error is encountered, these library functions set an
531 internal error number and signal the presence of the error by
532 returning an special return value.
533 The application can check the
534 current error number by calling
536 A human readable description of the recorded error is available by
539 .Ss Memory Management Rules
540 The library keeps track of all
544 descriptors associated with an ELF descriptor and recovers them
545 when the descriptor is closed using
547 Thus the application must not call
549 on data structures allocated by the ELF library.
551 Conversely the library will not
552 free data that it has not allocated.
553 As an example, an application may call
557 descriptor and can set the
559 member of the descriptor to point to a region of memory allocated
562 It is the applications responsibility to free this arena, though the
563 library will reclaim the space used by the
570 The original ELF(3) API was developed for Unix System V.
571 The current implementation of the ELF(3) API appeared in
574 The ELF library was written by
576 .Aq jkoshy@FreeBSD.org .