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elf_update(3elf)
elf_update(3ELF) 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
The elf_update() function causes the library to examine the information
associated with an ELF descriptor, elf, and to recalculate the struc‐
tural 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 struc‐
tures. Any modified structures are flagged with the
ELF_F_DIRTY bit. A program thus can update the struc‐
tural information and then reexamine them without chang‐
ing 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" informa‐
tion 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, coordinated, 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_flag‐
data(3ELF)). The sections' 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 created with elf_begin(), it must have
allowed writing the file. That is, the elf_begin() com‐
mand 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.
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:
tab(); lw(1.65i) lw(3.85i) MemberNotes
e_ident[EI_DATA]Library controls other e_ident values e_type e_machine
e_version e_entry e_phoffOnly when ELF_F_LAYOUT asserted e_shoffOnly
when ELF_F_LAYOUT asserted e_flags e_shstrndx
The following table shows the Program Header members:
tab(); lw(1.65i) lw(3.85i) MemberNotes
p_typeThe application controls all p_offsetprogram header entries
p_vaddr p_paddr p_filesz p_memsz p_flags p_align
The following table shows the Section Header members:
tab(); lw(1.65i) lw(3.85i) MemberNotes
sh_name sh_type sh_flags sh_addr sh_offsetOnly when ELF_F_LAYOUT
asserted sh_sizeOnly when ELF_F_LAYOUT asserted sh_link sh_info
sh_addralignOnly when ELF_F_LAYOUT asserted sh_entsize
The following table shows the Data Descriptor members:
tab(); lw(1.65i) lw(3.85i) MemberNotes
d_buf d_type d_size d_offOnly when ELF_F_LAYOUT asserted d_align d_ver‐
sion
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. Con‐
sequently, 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 sec‐
tion's most strictly aligned data buffer controls the section's align‐
ment. The library also inserts padding between buffers, as necessary,
to ensure the proper alignment of each buffer.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe
SEE ALSO
libelf(3LIB), elf32_xlatetof(3ELF), elf(3ELF), elf32_fsize(3ELF),
elf32_getehdr(3ELF), elf32_getshdr(3ELF), elf_begin(3ELF), elf_flag‐
data(3ELF), elf_getdata(3ELF), attributes(7)
NOTES
As mentioned above, the ELF_C_WRITE command translates data as neces‐
sary, before writing them to the file. This translation is not always
transparent to the application program. If a program has obtained
pointers to data associated with a file (for example, see elf32_gete‐
hdr(3ELF) and elf_getdata(3ELF)), the program should reestablish the
pointers after calling elf_update().
Oracle Solaris 11.4 11 Jul 2001 elf_update(3ELF)