SunOS man pages : elf_update (3)
ELF Library Functions elf_update(3ELF)
NAME
elf_update - update an ELF descriptor
SYNOPSIS
cc [ flag ... ] file ... -lelf [ library ... ]
#include <libelf.h>
off_t elf_update(Elf *elf, Elf_Cmd cmd);
DESCRIPTION
elf_update() causes the library to examine the information
associated with an ELF descriptor, elf, and to recalculate
the structural data needed to generate the file's image.
cmd may have the following values:
ELF_C_NULL
This value tells elf_update() to recalculate various
values, updating only the ELF descriptor's memory
structures. Any modified structures are flagged with
the ELF_F_DIRTY bit. A program thus can update the
structural information and then reexamine them without
changing the file associated with the ELF descriptor.
Because this does not change the file, the ELF
descriptor may allow reading, writing, or both reading
and writing (see elf_begin (3ELF)).
ELF_C_WRITE
If cmd has this value, elf_update() duplicates its
ELF_C_NULL actions and also writes any ``dirty''
information associated with the ELF descriptor to the
file. That is, when a program has used
elf_getdata(3ELF) or the elf_flagdata(3ELF) facilities
to supply new (or update existing) information for an
ELF descriptor, those data will be examined, coordi-
nated, translated if necessary (see
elf32_xlatetof(3ELF)), and written to the file. When
portions of the file are written, any ELF_F_DIRTY bits
are reset, indicating those items no longer need to be
written to the file (see elf_flagdata(3ELF)). The sec-
tions' data are written in the order of their section
header entries, and the section header table is writ-
ten to the end of the file. When the ELF descriptor
was created with elf_begin(), it must have allowed
writing the file. That is, the elf_begin() command
must have been either ELF_C_RDWR or ELF_C_WRITE.
If elf_update() succeeds, it returns the total size of the
file image (not the memory image), in bytes. Otherwise an
error occurred, and the function returns -1.
SunOS 5.8 Last change: 29 Dec 1996 1
ELF Library Functions elf_update(3ELF)
When updating the internal structures, elf_update() sets
some members itself. Members listed below are the
application's responsibility and retain the values given by
the program.
The following table shows ELF Header members:
Member Notes
e_ident[EI_DATA] Library controls other e_ident values
e_type
e_machine
e_version
e_entry
e_phoff Only when ELF_F_LAYOUT asserted
e_shoff Only when ELF_F_LAYOUT asserted
e_flags
e_shstrndx
The following table shows the Program Header members:
Member Notes
p_type The application controls all
p_offset program header entries
p_vaddr
p_paddr
p_filesz
p_memsz
p_flags
p_align
The following table shows the Section Header members:
Member Notes
sh_name
sh_type
sh_flags
sh_addr
sh_offset Only when ELF_F_LAYOUT asserted
sh_size Only when ELF_F_LAYOUT asserted
sh_link
sh_info
sh_addralign Only when ELF_F_LAYOUT asserted
sh_entsize
The following table shows the Data Descriptor members:
SunOS 5.8 Last change: 29 Dec 1996 2
ELF Library Functions elf_update(3ELF)
Member Notes
d_buf
d_type
d_size
d_off Only when ELF_F_LAYOUT asserted
d_align
d_version
Note that the program is responsible for two particularly
important members (among others) in the ELF header. The
e_version member controls the version of data structures
written to the file. If the version is EV_NONE, the library
uses its own internal version. The e_ident[EI_DATA] entry
controls the data encoding used in the file. As a special
case, the value may be ELFDATANONE to request the native
data encoding for the host machine. An error occurs in this
case if the native encoding doesn't match a file encoding
known by the library.
Further note that the program is responsible for the
sh_entsize section header member. Although the library sets
it for sections with known types, it cannot reliably know
the correct value for all sections. Consequently, the
library relies on the program to provide the values for
unknown section types. If the entry size is unknown or not
applicable, the value should be set to 0.
When deciding how to build the output file, elf_update()
obeys the alignments of individual data buffers to create
output sections. A section's most strictly aligned data
buffer controls the section's alignment. The library also
inserts padding between buffers, as necessary, to ensure the
proper alignment of each buffer.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
elf(3ELF), elf32_fsize(3ELF), elf32_getehdr(3ELF),
elf32_getshdr(3ELF), elf32_xlatetof(3ELF), elf_begin(3ELF),
elf_flagdata(3ELF), elf_getdata(3ELF), attributes(5)
SunOS 5.8 Last change: 29 Dec 1996 3
ELF Library Functions elf_update(3ELF)
NOTES
As mentioned above, the ELF_C_WRITE command translates data
as necessary, before writing them to the file. This transla-
tion is not always transparent to the application program.
If a program has obtained pointers to data associated with a
file (for example, see elf32_getehdr(3ELF) and
elf_getdata(3ELF)), the program should reestablish the
pointers after calling elf_update().
SunOS 5.8 Last change: 29 Dec 1996 4
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