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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
115 .Xr elf32_xlatetof 3 ,
116 .Xr elf32_xlatetom 3 ,
122 representations and also provides higher-level APIs that retrieve and store
123 data from the ELF object in a transparent manner.
124 .Ss Library Working Version
125 Conceptually, there are three version numbers associated with an
126 application using the ELF library to manipulate ELF objects:
127 .Bl -bullet -compact -offset indent
129 The ELF version that the application was compiled against.
130 This version determines the ABI expected by the application.
132 The ELF version of the ELF object being manipulated by the
133 application through the ELF library.
135 The ELF version (or set of versions) supported by the ELF library itself.
138 In order to facilitate working with ELF objects of differing versions,
139 the ELF library requires the application to call the
141 function before invoking many of its operations, in order to inform
142 the library of the application's desired working version.
144 In the current implementation, all three versions have to be
147 The ELF library uses the following prefixes:
148 .Bl -tag -width "ELF_F_*"
150 Used for class-independent functions.
152 Used for functions working with 32 bit ELF objects.
154 Used for functions working with 64 bit ELF objects.
156 Used for class-independent data types.
158 Used for command values used in a few functions.
159 These symbols are defined as members of the
163 Used for error numbers.
167 These constants define the kind of file associated with an ELF
171 The symbols are defined by the
175 These values are defined by the
177 enumeration, and denote the types of ELF data structures
178 that can be present in an ELF object.
181 Applications communicate with the library using descriptors.
183 .Bl -tag -width ".Vt Elf_Data"
187 descriptor represents an ELF object or an
190 It is allocated using one of the
197 descriptor can be used to read and write data to an ELF file.
200 descriptor can be associated with zero or more
204 Given an ELF descriptor, the application may retrieve the ELF
205 object's class-dependent
206 .Dq "Executable Header"
212 A new Ehdr structure may be allocated using the
219 .Dq "Program Header Table"
220 associated with an ELF descriptor may be allocated using the
225 A new program header table may be allocated or an existing table
234 structure is opaque and has no members visible to the
236 .\" TODO describe the Elf_Arhdr and Elf_Arsym structures.
240 data structure describes an individual chunk of a ELF file as
241 represented in memory.
242 It has the following application visible members:
243 .Bl -tag -width ".Vt unsigned int d_version" -compact
244 .It Vt "uint64_t d_align"
245 The in-file alignment of the data buffer within its containing ELF section.
246 This value must be a power of two.
247 .It Vt "uint64_t d_off"
248 The offset with the containing section where this descriptors data
250 This field will be computed by the library unless the application
251 requests full control of the ELF object's layout.
252 .It Vt "uint64_t d_size"
253 The number of bytes of data in this descriptor.
255 A pointer to data in memory.
256 .It Vt "Elf_Type d_type"
257 The ELF type (see below) of the data in this descriptor.
258 .It Vt "unsigned int d_version"
259 The operating version for the data in this buffer.
263 descriptors are usually associated with
266 Existing data descriptors associated with an ELF section may be
267 structures are retrieved using the
272 function may be used to attach new data descriptors to an ELF section.
275 descriptors represent a section in an ELF object.
277 They are retrieved using the
280 An application may iterate through the existing sections of an ELF
284 New sections may be allocated using the
290 descriptor is opaque and contains no application modifiable fields.
292 .Ss Supported Elf Types
293 The following ELF datatypes are supported by the library.
295 .Bl -tag -width ".Dv ELF_T_SYMINFO" -compact
300 The library will not attempt to translate byte data.
302 Software and hardware capability records.
304 Records used in a section of type
307 ELF executable header.
309 16-bit unsigned words.
311 64 bit unsigned words.
314 .\".It Dv ELF_T_MOVEP
315 .\" As yet unsupported.
321 ELF program header table entries.
323 ELF relocation entries.
325 ELF relocation entries with addends.
327 ELF section header entries.
333 ELF symbol information.
335 ELF symbol table entries.
337 Symbol version definition records.
339 Symbol version requirement records.
341 Unsigned 32-bit words.
343 Unsigned 64-bit words.
348 denotes the number of Elf types known to the library.
350 The following table shows the mapping between ELF section types
353 and the types supported by the library.
354 .Bl -column ".Dv SHT_PREINIT_ARRAY" ".Dv ELF_T_SYMINFO"
355 .It Em Section Type Ta Em "Library Type" Ta Em Description
356 .It Dv SHT_DYNAMIC Ta Dv ELF_T_DYN Ta Xo
360 .It Dv SHT_DYNSYM Ta Dv ELF_T_SYM Ta Symbols for dynamic linking.
361 .It Dv SHT_FINI_ARRAY Ta Dv ELF_T_ADDR Ta Termination function pointers.
362 .It Dv SHT_GROUP Ta Dv ELF_T_WORD Ta Section group marker.
363 .It Dv SHT_HASH Ta Dv ELF_T_HASH Ta Symbol hashes.
364 .It Dv SHT_INIT_ARRAY Ta Dv ELF_T_ADDR Ta Initialization function pointers.
365 .It Dv SHT_NOBITS Ta Dv ELF_T_BYTE Ta Xo
370 .It Dv SHT_NOTE Ta Dv ELF_T_NOTE Ta ELF note records.
371 .It Dv SHT_PREINIT_ARRAY Ta Dv ELF_T_ADDR Ta Pre-initialization function pointers.
372 .It Dv SHT_PROGBITS Ta Dv ELF_T_BYTE Ta Machine code.
373 .It Dv SHT_REL Ta Dv ELF_T_REL Ta ELF relocation records.
374 .It Dv SHT_RELA Ta Dv ELF_T_RELA Ta Relocation records with addends.
375 .It Dv SHT_STRTAB Ta Dv ELF_T_BYTE Ta String tables.
376 .It Dv SHT_SYMTAB Ta Dv ELF_T_SYM Ta Symbol tables.
377 .It Dv SHT_SYMTAB_SHNDX Ta Dv ELF_T_WORD Ta Used with extended section numbering.
378 .It Dv SHT_GNU_verdef Ta Dv ELF_T_VDEF Ta Symbol version definitions.
379 .It Dv SHT_GNU_verneed Ta Dv ELF_T_VNEED Ta Symbol versioning requirements.
380 .It Dv SHT_GNU_versym Ta Dv ELF_T_HALF Ta Version symbols.
381 .It Dv SHT_SUNW_move Ta Dv ELF_T_MOVE Ta ELF move records.
382 .It Dv SHT_SUNW_syminfo Ta Dv ELF_T_SYMINFO Ta Additional symbol flags.
384 .Ss Functional Grouping
385 This section contains a brief overview of the available functionality
387 Each function listed here is described further in its own manual page.
388 .Bl -tag -width indent
392 Retrieve the archive symbol table.
394 Retrieve the archive header for an object.
396 Retrieve the offset of a member inside an archive.
402 Random access inside an
406 .It "Data Structures"
409 Retrieve translated data for an ELF section.
411 Retrieve the section descriptor for a named section.
413 Retrieve the index for a section.
417 descriptor to an ELF section.
419 Add a new section descriptor to an ELF descriptor.
421 Iterate through the sections in an ELF object.
423 Retrieve untranslated data for an ELF sectino.
425 Return a pointer to the untranslated file contents for an ELF object.
426 .It Fn elf32_getehdr , Fn elf64_getehdr
427 Retrieve the Executable Header in an ELF object.
428 .It Fn elf32_getphdr , Fn elf64_getphdr
429 Retrieve the Program Header Table in an ELF object.
430 .It Fn elf32_getshdr , Fn elf64_getshdr
431 Retrieve the ELF section header associated with an
434 .It Fn elf32_newehdr , Fn elf64_newehdr
435 Allocate an Executable Header in an ELF object.
436 .It Fn elf32_newphdr , Fn elf64_newphdr
437 Allocate or resize the Program Header Table in an ELF object.
439 .It "Data Translation"
441 .It Fn elf32_xlatetof , Fn elf64_xlatetof
442 Translate an ELF data structure from its native representation to its
444 .It Fn elf32_xlatetom , Fn elf64_xlatetom
445 Translate an ELF data structure from its file representation to a
446 native representation.
448 .It "Error Reporting"
451 Retrieve the current error.
453 Retrieve a human readable description of the current error.
460 archive or ELF object given a file descriptor.
462 Close an ELF descriptor and release all its resources.
466 archive or ELF object present in a memory area.
468 Sets the operating version.
471 .Bl -tag -width ".Fn elf_setshstrndx" -compact
473 Manage the association between and ELF descriptor and its underlying file.
479 Mark the ELF Executable Header in an ELF descriptor as dirty.
481 Mark the ELF Program Header Table in an ELF descriptor as dirty.
487 Mark an ELF Section Header as dirty.
488 .It Fn elf_setshstrndx
489 Set the index of the section name string table for the ELF object.
491 Recompute ELF object layout and optionally write the modified object
492 back to the underlying file.
495 .Bl -tag -width ".Fn elf_getshstrndx" -compact
496 .It Fn elf32_checksum , Fn elf64_checkum
497 Compute checksum of an ELF object.
499 Retrieve the identification bytes for an ELF object.
501 Retrieve the number of sections in an ELF object.
502 .It Fn elf_getshstrndx
503 Retrieve the section index of the section name string table in
506 Compute the ELF hash value of a string.
508 Query the kind of object associated with an ELF descriptor.
509 .It Fn elf32_fsize , Fn elf64_fsize
510 Return the size of the file representation of an ELF type.
513 .Ss Controlling ELF Object Layout
514 In the usual mode of operation, library will compute section
515 offsets and alignments based on the contents of an ELF descriptor's
516 sections without need for further intervention by the
519 However, if the application wishes to take complete charge of the
520 layout of the ELF file, it may set the
522 flag on an ELF descriptor using
524 following which the library will use the data offsets and alignments
525 specified by the application when laying out the file.
526 Application control of file layout is described further in the
530 Gaps in between sections will be filled with the fill character
534 In case an error is encountered, these library functions set an
535 internal error number and signal the presence of the error by
536 returning an special return value.
537 The application can check the
538 current error number by calling
540 A human readable description of the recorded error is available by
543 .Ss Memory Management Rules
544 The library keeps track of all
548 descriptors associated with an ELF descriptor and recovers them
549 when the descriptor is closed using
551 Thus the application must not call
553 on data structures allocated by the ELF library.
555 Conversely the library will not
556 free data that it has not allocated.
557 As an example, an application may call
561 descriptor and can set the
563 member of the descriptor to point to a region of memory allocated
566 It is the applications responsibility to free this area, though the
567 library will reclaim the space used by the
574 The original ELF(3) API was developed for Unix System V.
575 The current implementation of the ELF(3) API appeared in
578 The ELF library was written by
580 .Aq jkoshy@FreeBSD.org .