ELF Library Functions elf_update(3ELF)
NAME
elf_update - update an ELF descriptor
SYNOPSIS
cc [ flag ... ] file ... -lelf [ library ... ]
#include
off_t elf_update(Elf *elf, Elf_Cmd cmd);
DESCRIPTION
The elf_update() function 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. The cmd argument can 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 modifiedstructures 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 (seeelf_begin(3ELF)).
ELF_C_WRITE If cmd has this value, elf_update() dupli-
cates its ELF_C_NULL actions and also writes
any ``dirty'' information associated with the ELF descriptor to the file. That is, when aprogram 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, coordinated, translated if necessary (seeelf32_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 tothe 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 written to the end of the file. When the ELF descriptor was createdwith elf_begin(), it must have allowed writ-
ing the file. That is, the elf_begin()
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ELF Library Functions elf_update(3ELF)
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 anerror occurred, and the function returns -1.
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 Notese_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 Notesp_type The application controls all
p_offset program header entries
p_vaddr
p_paddr
p_filesz
p_memsz
p_flags
p_align
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ELF Library Functions elf_update(3ELF)
The following table shows the Section Header members: Member Notessh_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: Member Notesd_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. Thee_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 thesh_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 notSunOS 5.11 Last change: 11 Jul 2001 3
ELF Library Functions elf_update(3ELF)
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 |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| 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), libelf(3LIB), attri-
butes(5) NOTESAs 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 afile (for example, see elf32_getehdr(3ELF) and
elf_getdata(3ELF)), the program should reestablish the
pointers after calling elf_update().
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