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31 .Nd API for manipulating ELF objects
39 provides functions that allow an application to read and manipulate
40 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 In addition, the library uses symbols with prefixes
183 for its internal use.
185 Applications communicate with the library using descriptors.
187 .Bl -tag -width ".Vt Elf_Data"
191 descriptor represents an ELF object or an
194 It is allocated using one of the
201 descriptor can be used to read and write data to an ELF file.
204 descriptor can be associated with zero or more
208 Given an ELF descriptor, the application may retrieve the ELF
209 object's class-dependent
210 .Dq "Executable Header"
216 A new Ehdr structure may be allocated using the
223 .Dq "Program Header Table"
224 associated with an ELF descriptor may be allocated using the
229 A new program header table may be allocated or an existing table
238 structure is opaque and has no members visible to the
240 .\" TODO describe the Elf_Arhdr and Elf_Arsym structures.
244 data structure describes an individual chunk of a ELF file as
245 represented in memory.
246 It has the following application-visible members:
247 .Bl -tag -width ".Vt unsigned int d_version" -compact
248 .It Vt "uint64_t d_align"
249 The in-file alignment of the data buffer within its containing ELF section.
250 This value must be non-zero and a power of two.
252 A pointer to data in memory.
253 .It Vt "uint64_t d_off"
254 The offset within the containing section where this descriptor's data
256 This field will be computed by the library unless the application
257 requests full control of the ELF object's layout.
258 .It Vt "uint64_t d_size"
259 The number of bytes of data in this descriptor.
260 .It Vt "Elf_Type d_type"
261 The ELF type (see below) of the data in this descriptor.
262 .It Vt "unsigned int d_version"
263 The operating version for the data in this buffer.
267 descriptors are usually associated with
270 Existing data descriptors associated with an ELF section may be
271 structures are retrieved using the
278 function may be used to attach new data descriptors to an ELF section.
281 descriptors represent a section in an ELF object.
283 They are retrieved using the
286 An application may iterate through the existing sections of an ELF
290 New sections may be allocated using the
296 descriptor is opaque and contains no application modifiable fields.
298 .Ss Supported Elf Types
299 The following ELF datatypes are supported by the library.
301 .Bl -tag -width ".Dv ELF_T_SYMINFO" -compact
306 The library will not attempt to translate byte data.
308 Software and hardware capability records.
310 Records used in a section of type
313 ELF executable header.
315 GNU-style hash tables.
317 16-bit unsigned words.
319 64 bit unsigned words.
322 .\".It Dv ELF_T_MOVEP
323 .\" As yet unsupported.
329 ELF program header table entries.
331 ELF relocation entries.
333 ELF relocation entries with addends.
335 ELF section header entries.
341 ELF symbol information.
343 ELF symbol table entries.
345 Symbol version definition records.
347 Symbol version requirement records.
349 Unsigned 32-bit words.
351 Unsigned 64-bit words.
356 denotes the number of Elf types known to the library.
358 The following table shows the mapping between ELF section types
361 and the types supported by the library.
362 .Bl -column ".Dv SHT_PREINIT_ARRAY" ".Dv ELF_T_SYMINFO"
363 .It Em Section Type Ta Em "Library Type" Ta Em Description
364 .It Dv SHT_DYNAMIC Ta Dv ELF_T_DYN Ta Xo
368 .It Dv SHT_DYNSYM Ta Dv ELF_T_SYM Ta Symbols for dynamic linking.
369 .It Dv SHT_FINI_ARRAY Ta Dv ELF_T_ADDR Ta Termination function pointers.
370 .It Dv SHT_GROUP Ta Dv ELF_T_WORD Ta Section group marker.
371 .It Dv SHT_HASH Ta Dv ELF_T_HASH Ta Symbol hashes.
372 .It Dv SHT_INIT_ARRAY Ta Dv ELF_T_ADDR Ta Initialization function pointers.
373 .It Dv SHT_NOBITS Ta Dv ELF_T_BYTE Ta Xo
378 .It Dv SHT_NOTE Ta Dv ELF_T_NOTE Ta ELF note records.
379 .It Dv SHT_PREINIT_ARRAY Ta Dv ELF_T_ADDR Ta Pre-initialization function pointers.
380 .It Dv SHT_PROGBITS Ta Dv ELF_T_BYTE Ta Machine code.
381 .It Dv SHT_REL Ta Dv ELF_T_REL Ta ELF relocation records.
382 .It Dv SHT_RELA Ta Dv ELF_T_RELA Ta Relocation records with addends.
383 .It Dv SHT_STRTAB Ta Dv ELF_T_BYTE Ta String tables.
384 .It Dv SHT_SYMTAB Ta Dv ELF_T_SYM Ta Symbol tables.
385 .It Dv SHT_SYMTAB_SHNDX Ta Dv ELF_T_WORD Ta Used with extended section numbering.
386 .It Dv SHT_GNU_verdef Ta Dv ELF_T_VDEF Ta Symbol version definitions.
387 .It Dv SHT_GNU_verneed Ta Dv ELF_T_VNEED Ta Symbol versioning requirements.
388 .It Dv SHT_GNU_versym Ta Dv ELF_T_HALF Ta Version symbols.
389 .It Dv SHT_SUNW_move Ta Dv ELF_T_MOVE Ta ELF move records.
390 .It Dv SHT_SUNW_syminfo Ta Dv ELF_T_SYMINFO Ta Additional symbol flags.
393 .Ss Functional Grouping
394 This section contains a brief overview of the available functionality
396 Each function listed here is described further in its own manual page.
397 .Bl -tag -width indent
401 Retrieve the archive symbol table.
403 Retrieve the archive header for an object.
405 Retrieve the offset of a member inside an archive.
411 Random access inside an
415 .It "Data Structures"
418 Retrieve translated data for an ELF section.
420 Retrieve the section descriptor for a named section.
422 Retrieve the index for a section.
426 descriptor to an ELF section.
428 Add a new section descriptor to an ELF descriptor.
430 Iterate through the sections in an ELF object.
432 Retrieve untranslated data for an ELF section.
434 Return a pointer to the untranslated file contents for an ELF object.
435 .It Fn elf32_getehdr , Fn elf64_getehdr
436 Retrieve the Executable Header in an ELF object.
437 .It Fn elf32_getphdr , Fn elf64_getphdr
438 Retrieve the Program Header Table in an ELF object.
439 .It Fn elf32_getshdr , Fn elf64_getshdr
440 Retrieve the ELF section header associated with an
443 .It Fn elf32_newehdr , Fn elf64_newehdr
444 Allocate an Executable Header in an ELF object.
445 .It Fn elf32_newphdr , Fn elf64_newphdr
446 Allocate or resize the Program Header Table in an ELF object.
448 .It "Data Translation"
450 .It Fn elf32_xlatetof , Fn elf64_xlatetof
451 Translate an ELF data structure from its native representation to its
453 .It Fn elf32_xlatetom , Fn elf64_xlatetom
454 Translate an ELF data structure from its file representation to a
455 native representation.
457 .It "Error Reporting"
460 Retrieve the current error.
462 Retrieve a human readable description of the current error.
469 archive or ELF object given a file descriptor.
471 Close an ELF descriptor and release all its resources.
475 archive or ELF object present in a memory arena.
477 Sets the operating version.
480 .Bl -tag -width ".Fn elf_setshstrndx" -compact
482 Manage the association between and ELF descriptor and its underlying file.
488 Mark the ELF Executable Header in an ELF descriptor as dirty.
490 Mark the ELF Program Header Table in an ELF descriptor as dirty.
496 Mark an ELF Section Header as dirty.
497 .It Fn elf_setshstrndx
498 Set the index of the section name string table for the ELF object.
500 Recompute ELF object layout and optionally write the modified object
501 back to the underlying file.
504 .Bl -tag -width ".Fn elf_getshstrndx" -compact
505 .It Fn elf32_checksum , Fn elf64_checkum
506 Compute checksum of an ELF object.
508 Retrieve the identification bytes for an ELF object.
510 Retrieve the number of sections in an ELF object.
511 .It Fn elf_getshstrndx
512 Retrieve the section index of the section name string table in
515 Compute the ELF hash value of a string.
517 Query the kind of object associated with an ELF descriptor.
518 .It Fn elf32_fsize , Fn elf64_fsize
519 Return the size of the file representation of an ELF type.
522 .Ss Controlling ELF Object Layout
523 In the usual mode of operation, library will compute section
524 offsets and alignments based on the contents of an ELF descriptor's
525 sections without need for further intervention by the
528 However, if the application wishes to take complete charge of the
529 layout of the ELF file, it may set the
531 flag on an ELF descriptor using
533 following which the library will use the data offsets and alignments
534 specified by the application when laying out the file.
535 Application control of file layout is described further in the
539 Gaps in between sections will be filled with the fill character
543 In case an error is encountered, these library functions set an
544 internal error number and signal the presence of the error by
545 returning an special return value.
546 The application can check the
547 current error number by calling
549 A human readable description of the recorded error is available by
552 .Ss Memory Management Rules
553 The library keeps track of all
557 descriptors associated with an ELF descriptor and recovers them
558 when the descriptor is closed using
560 Thus the application must not call
562 on data structures allocated by the ELF library.
564 Conversely the library will not
565 free data that it has not allocated.
566 As an example, an application may call
570 descriptor and can set the
572 member of the descriptor to point to a region of memory allocated
575 It is the applications responsibility to free this arena, though the
576 library will reclaim the space used by the
583 The original ELF(3) API was developed for Unix System V.
584 The current implementation of the ELF(3) API appeared in
587 The ELF library was written by
589 .Aq jkoshy@FreeBSD.org .