ELF(3) | Library Functions Manual | ELF(3) |
elf
—
#include <libelf.h>
This manual page serves to provide an overview of the
functionality in the ELF library. Further information may found in the
manual pages for individual elf
functions that
comprise the library.
ELF objects have an associated “ELF class” which
denotes the natural machine word size for the architecture the object is
associated with. Objects for 32 bit architectures have an ELF class of
ELFCLASS32
. Objects for 64 bit architectures have an
ELF class of ELFCLASS64
.
ELF objects also have an associated “endianness”
which denotes the endianness of the machine architecture associated with the
object. This may be ELFDATA2LSB
for little-endian
architectures and ELFDATA2MSB
for big-endian
architectures.
ELF objects are also associated with an API version number. This version number determines the layout of the individual components of an ELF file and the semantics associated with these.
elf
library distinguishes between
“native” representations of ELF data structures and their
“file” representations.
An application would work with ELF data in its “native” representation, i.e., using the native byteorder and alignment mandated by the processor the application is running on. The “file” representation of the same data could use a different byte ordering and follow different constraints on object alignment than these native constraints.
Accordingly, the elf
library offers
translation facilities
(elf32_xlatetof(3),
elf32_xlatetom(3),
elf64_xlatetof(3) and
elf64_xlatetom(3)) to
and from these representations and also provides higher-level APIs that
retrieve and store data from the ELF object in a transparent manner.
In order to facilitate working with ELF objects of differing
versions, the ELF library requires the application to call the
elf_version
() function before invoking many of its
operations, in order to inform the library of the application's desired
working version.
In the current implementation, all three versions have to be
EV_CURRENT
.
elf_
elf32_
elf64_
Elf_
ELF_C_
Elf_Cmd
enumeration.ELF_E_
ELF_F_
ELF_K_
ELF_T_
In addition, the library uses symbols with prefixes
_ELF
and _libelf
for its
internal use.
elf_begin
() or
elf_memory
() functions. An
Elf descriptor can be used to read and write data to
an ELF file. An Elf descriptor can be associated
with zero or more Elf_Scn section descriptors.
Given an ELF descriptor, the application may retrieve the ELF
object's class-dependent “Executable Header” structures
using the elf32_getehdr
() or
elf64_getehdr
() functions. A new Ehdr structure
may be allocated using the elf64_newehdr
() or
elf64_newehdr
() functions.
The “Program Header Table” associated with an
ELF descriptor may be allocated using the
elf32_getphdr
() or
elf64_getphdr
() functions. A new program header
table may be allocated or an existing table resized using the
elf32_newphdr
() or
elf64_newphdr
() functions.
The Elf structure is opaque and has no members visible to the application.
Elf_Data descriptors are usually
associated with Elf_Scn descriptors. Existing data
descriptors associated with an ELF section may be structures are
retrieved using the elf_getdata
() and
elf_rawdata
() functions. The
elf_newdata
() function may be used to attach new
data descriptors to an ELF section.
They are retrieved using the
elf_getscn
() function. An application may
iterate through the existing sections of an ELF object using the
elf_nextscn
() function. New sections may be
allocated using the elf_newscn
() function.
The Elf_Scn descriptor is opaque and contains no application modifiable fields.
ELF_T_ADDR
ELF_T_BYTE
ELF_T_CAP
ELF_T_DYN
SHT_DYNAMIC
.ELF_T_EHDR
ELF_T_GNUHASH
ELF_T_HALF
ELF_T_LWORD
ELF_T_MOVE
ELF_T_NOTE
ELF_T_OFF
ELF_T_PHDR
ELF_T_REL
ELF_T_RELA
ELF_T_SHDR
ELF_T_SWORD
ELF_T_SXWORD
ELF_T_SYMINFO
ELF_T_SYM
ELF_T_VDEF
ELF_T_VNEED
ELF_T_WORD
ELF_T_XWORD
The symbol ELF_T_NUM
denotes the number of
Elf types known to the library.
The following table shows the mapping between ELF section types defined in elf(5) and the types supported by the library.
Section Type | Library Type | Description |
SHT_DYNAMIC |
ELF_T_DYN |
‘.dynamic’ section entries. |
SHT_DYNSYM |
ELF_T_SYM |
Symbols for dynamic linking. |
SHT_FINI_ARRAY |
ELF_T_ADDR |
Termination function pointers. |
SHT_GNU_HASH |
ELF_T_GNUHASH |
GNU hash sections. |
SHT_GNU_LIBLIST |
ELF_T_WORD |
List of libraries to be pre-linked. |
SHT_GNU_verdef |
ELF_T_VDEF |
Symbol version definitions. |
SHT_GNU_verneed |
ELF_T_VNEED |
Symbol versioning requirements. |
SHT_GNU_versym |
ELF_T_HALF |
Version symbols. |
SHT_GROUP |
ELF_T_WORD |
Section group marker. |
SHT_HASH |
ELF_T_HASH |
Symbol hashes. |
SHT_INIT_ARRAY |
ELF_T_ADDR |
Initialization function pointers. |
SHT_NOBITS |
ELF_T_BYTE |
Empty sections. See elf(5). |
SHT_NOTE |
ELF_T_NOTE |
ELF note records. |
SHT_PREINIT_ARRAY |
ELF_T_ADDR |
Pre-initialization function pointers. |
SHT_PROGBITS |
ELF_T_BYTE |
Machine code. |
SHT_REL |
ELF_T_REL |
ELF relocation records. |
SHT_RELA |
ELF_T_RELA |
Relocation records with addends. |
SHT_STRTAB |
ELF_T_BYTE |
String tables. |
SHT_SYMTAB |
ELF_T_SYM |
Symbol tables. |
SHT_SYMTAB_SHNDX |
ELF_T_WORD |
Used with extended section numbering. |
SHT_SUNW_dof |
ELF_T_BYTE |
Used by dtrace(1). |
SHT_SUNW_move |
ELF_T_MOVE |
ELF move records. |
SHT_SUNW_syminfo |
ELF_T_SYMINFO |
Additional symbol flags. |
SHT_SUNW_verdef |
ELF_T_VDEF |
Same as SHT_GNU_verdef . |
SHT_SUNW_verneed |
ELF_T_VNEED |
Same as SHT_GNU_verneed . |
SHT_SUNW_versym |
ELF_T_HALF |
Same as SHT_GNU_versym . |
Section types in the range [SHT_LOOS
,
SHT_HIUSER
] are otherwise considered to be of type
ELF_T_BYTE
.
elf_getdata
()elf_getscn
()elf_ndxscn
()elf_newdata
()elf_newscn
()elf_nextscn
()elf_rawdata
()elf_rawfile
()elf32_getehdr
(),
elf64_getehdr
()elf32_getphdr
(),
elf64_getphdr
()elf32_getshdr
(),
elf64_getshdr
()elf32_newehdr
(),
elf64_newehdr
()elf32_newphdr
(),
elf64_newphdr
()elf32_xlatetof
(),
elf64_xlatetof
()elf32_xlatetom
(),
elf64_xlatetom
()elf_errno
()elf_errmsg
()elf_cntl
()elf_flagdata
()elf_flagehdr
()elf_flagphdr
()elf_flagscn
()elf_flagshdr
()elf_setshstrndx
()elf_update
()elf32_checksum
(),
elf64_checkum
()elf_getident
()elf_getshnum
()elf_getshstrndx
()elf_hash
()elf_kind
()elf32_fsize
(),
elf64_fsize
()However, if the application wishes to take complete charge of the
layout of the ELF file, it may set the ELF_F_LAYOUT
flag on an ELF descriptor using
elf_flagelf(3), following
which the library will use the data offsets and alignments specified by the
application when laying out the file. Application control of file layout is
described further in the
elf_update(3) manual
page.
Gaps in between sections will be filled with the fill character
set by function elf_fill
().
Conversely the library will not free data that it has not allocated. As an example, an application may call elf_newdata(3) to allocate a new Elf_Data descriptor and can set the d_off member of the descriptor to point to a region of memory allocated using malloc(3). It is the applications responsibility to free this arena, though the library will reclaim the space used by the Elf_Data descriptor itself.
July 28, 2014 | NetBSD 9.2 |