ELF_UPDATE(3)

NAME
elf_update - update an ELF descriptor

LIBRARY
libelf

SYNOPSIS
#include <libelf.h>
off_t
elf_update(Elf *elf, Elf_Cmd cmd);

DESCRIPTION
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 values:

ELF_C_NULL
    The library will recalculate structural information flagging modified structures with the ELF_F_DIRTY flag, but will not write back data to the underlying file image.

ELF_C_WRITE
    The library will recalculate structural information and will also write the new image to the underlying file.

  File Layout
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 ELF file:

Executable Header
    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 in <sys/elf_common.h>.
    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 <sys/elf_common.h>.
    e_version
        Set to the desired version of the ELF object.

Program Header
    All fields of the entries in the program header table are under application control.

Section Header
    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 elements, 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 section names.
    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 elf_fill(3).

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 coverage 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().

RETURN VALUES
Function elf_update() returns the total size of the file image if successful, or -1 if an error occurred.

ERRORS
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 incompatible 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 file.

[ELF_E_VERSION]
    Argument elf had an unsupported version or contained an Elf_Data descriptor with an unsupported version.

SEE ALSO
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)