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elf_update (3)
  • >> elf_update (3) ( Solaris man: Библиотечные вызовы )
  • elf_update (3) ( FreeBSD man: Библиотечные вызовы )
  •  

    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 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 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, 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_flagdata(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() 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.

    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:

    MemberNotes

    e_ident[EI_DATA]
    e_type
    e_machine
    e_version
    e_entry
    e_phoff
    e_shoff
    e_flags
    e_shstrndx

    The following table shows the Program Header members:

    MemberNotes

    p_type
    p_offset
    p_vaddr
    p_paddr
    p_filesz
    p_memsz
    p_flags
    p_align

    The following table shows the Section Header members:

    MemberNotes

    sh_name
    sh_type
    sh_flags
    sh_addr
    sh_offset
    sh_size
    sh_link
    sh_info
    sh_addralign
    sh_entsize

    The following table shows the Data Descriptor members:

    MemberNotes

    d_buf
    d_type
    d_size
    d_off
    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 attributes:

    ATTRIBUTE TYPEATTRIBUTE VALUE

    Interface StabilityStable

    MT-Level

     

    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), attributes(5)  

    NOTES

    As mentioned above, the ELF_C_WRITE command translates data as necessary, 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_getehdr(3ELF) and elf_getdata(3ELF)), the program should reestablish the pointers after calling elf_update().


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    ATTRIBUTES
    SEE ALSO
    NOTES


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