As
elf(S-osr5)
explains,
ELF
provides a framework for various classes of files,
where basic objects may have 32 bits,
64 bits, and so forth.
To accommodate these differences, without forcing the
larger sizes on smaller machines, the initial bytes in an
ELF
file hold identification information common to all file classes.
Every
ELF
header's
e_ident
has EI_NIDENT bytes
with the following interpretation.
e_ident
Index
Value
Purpose
EI_MAG0
ELFMAG0
File identification
EI_MAG1
ELFMAG1
EI_MAG2
ELFMAG2
EI_MAG3
ELFMAG3
EI_CLASS
ELFCLASSNONE
File class
ELFCLASS32
ELFCLASS64
EI_DATA
ELFDATANONE
Data encoding
ELFDATA2LSB
ELFDATA2MSB
EI_VERSION
EV_CURRENT
File version
7-15
0
Unused, set to zero
Other kinds of files (see
elf_kind(S-osr5)
may also have identification data, though they would not conform to
e_ident.
elf_getident(S-osr5)
returns a pointer to the file's ``initial bytes.''
If the library recognizes the file,
a conversion from the file image to the memory image may occur.
In any case, the identification bytes are guaranteed to be unchanged,
though the size of the unmodified area depends on the file type.
If
ptr
is non-null,
the library stores the number of identification bytes in the location that
ptr
points to. If no data is present,
elf
is null, or an error occurs, the return value is a null pointer,
with zero optionally stored through
ptr.
Diagnostics
Error conditions are identified through the routine
elf_error(S-osr5).