ELF_UPDATE(3) BSD Library Functions Manual ELF_UPDATE(3)
elf_update -- update an ELF descriptor
elf_update(Elf *elf, Elf_Cmd cmd);
Function elf_update() causes the library to recalculate the structure of an ELF object and
optionally write out the image of the object to file.
Argument elf is a descriptor to an ELF object. Argument cmd can take on the following val-
ELF_C_NULL The library will recalculate structural information flagging modified struc-
tures with the ELF_F_DIRTY flag, but will not write back data to the underlying
ELF_C_WRITE The library will recalculate structural information and will also write the new
image to the underlying file.
If the ELF_F_LAYOUT flag has been set on the ELF descriptor, the application assumes full
responsibility for the layout of the ELF object. If this flag is not set, the ELF library
will compute the layout of the file from its associated section descriptors.
It is the application's responsibility to manage the the following structure members in the
The ELF executable header is described in elf(5). The following members of the ELF
executable header are the application's responsibility:
e_entry Set to the desired entry address for executables.
e_flags Set to the desired processor specific flags.
e_ident[EI_DATA] Must be set to one of ELFDATA2LSB or ELFDATA2MSB.
e_ident[EI_OSABI] Set to the OS ABI desired. For FreeBSD executables, this field
should be set to ELFOSABI_FREEBSD.
e_machine Set to the desired machine architecture, one of the EM_* values
e_phoff If the application is managing the object's layout, it must set
this field to the file offset of the ELF program header table.
e_shoff If the application is managing the object's layout, it must set
this field to the file offset of the ELF section header table.
e_shstrndx Set to the index of the string table containing section names.
e_type Set to the type of the ELF object, one of the ET_* values in
e_version Set to the desired version of the ELF object.
All fields of the entries in the program header table are under application control.
The ELF section header is described in elf(5). The following members of the ELF
section header are the application's responsibility:
sh_addr Set to the physical memory address where the section should reside.
sh_addralign If the application is managing the file layout, it must set this field
to the desired alignment for the section's contents. This value must
be a power of two.
sh_entsize Set to the size of each entry, for sections containing fixed size ele-
ments, or set to zero for sections without fixed size elements. If
the application is not managing file layout, it may leave this field
as zero for those sections whose types known to the library.
sh_flags Set to the desired section flags.
sh_info Set as described in elf(5).
sh_link Set as described in elf(5).
sh_name Set to the index of the section's name in the string table containing
sh_offset If the application is managing the file layout, it must set this field
to the file offset of the section's contents.
sh_size If the application is managing the file layout, it must set this field
to the file size of the section's contents.
sh_type Set to the type of the section.
Gaps in the coverage of the file's contents will be set to the fill value specified by
If the application has requested full control over the file's layout by setting the
ELF_F_LAYOUT flag on the ELF descriptor, it should ensure that there are no gaps in the cov-
erage of the file's contents.
All pointers to Elf_Scn and Elf_Data descriptors associated with descriptor elf should be
considered as invalid after a call to elf_update().
Function elf_update() returns the total size of the file image if successful, or -1 if an
This function may fail with the following errors:
[ELF_E_ARGUMENT] Argument elf was null.
[ELF_E_ARGUMENT] Argument cmd was not recognized.
[ELF_E_ARGUMENT] The argument elf was not a descriptor for an ELF object.
[ELF_E_CLASS] The e_ident[EI_CLASS] field of the executable header of argument elf did
not match the class of the file.
[ELF_E_DATA] An Elf_Data descriptor contained in argument elf specified a type incom-
patible with its containing section.
[ELF_E_HEADER] The ELF header in argument elf requested a different byte order from the
byte order already associated with the file.
[ELF_E_IO] An I/O error was encountered.
[ELF_E_LAYOUT] An Elf_Data descriptor contained in argument elf specified an alignment
incompatible with its containing section.
[ELF_E_LAYOUT] Argument elf contained section descriptors that overlapped in extent.
[ELF_E_LAYOUT] Argument elf contained section descriptors that were incorrectly aligned
or were too small for their data.
[ELF_E_LAYOUT] The flag ELF_F_LAYOUT was set on the Elf descriptor and the section header
table overlapped an extent in the object mapped by a section descriptor.
[ELF_E_MODE] An ELF_C_WRITE operation was requested with an ELF descriptor that was not
opened for writing or updating.
[ELF_E_SECTION] Argument elf contained a section with an unrecognized type.
[ELF_E_SECTION] The section header at index SHN_UNDEF had an illegal section type.
[ELF_E_SEQUENCE] An ELF_C_WRITE operation was requested after a prior call to elf_cntl(elf,
ELF_C_FDDONE) disassociated the ELF descriptor elf from its underlying
[ELF_E_VERSION] Argument elf had an unsupported version or contained an Elf_Data descrip-
tor with an unsupported version.
elf(3), elf32_getehdr(3), elf32_getphdr(3), elf32_newehdr(3), elf32_newphdr(3),
elf64_getehdr(3), elf64_getphdr(3), elf64_newehdr(3), elf64_newphdr(3), elf_cntl(3),
elf_fill(3), elf_flagehdr(3), elf_flagelf(3), elf_getdata(3), elf_getscn(3), elf_newdata(3),
elf_newscn(3), elf_rawdata(3), gelf(3), gelf_newehdr(3), gelf_newphdr(3), elf(5)
BSD March 19, 2008 BSD