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elf (3)
  • elf (3) ( Solaris man: Библиотечные вызовы )
  • >> elf (3) ( FreeBSD man: Библиотечные вызовы )
  • elf (5) ( FreeBSD man: Форматы файлов )
  • elf (5) ( Linux man: Форматы файлов )
  • Ключ elf обнаружен в базе ключевых слов.

  • BSD mandoc
     

    NAME

    elf
    
     - API for manipulating ELF objects
    
     
    

    LIBRARY

    Lb libelf
    
     
    

    SYNOPSIS

       #include <libelf.h>
     

    DESCRIPTION

    The Lb libelf library provides functions that allow an application to read and manipulate ELF object files, and to read ar(1) archives. The library allows the manipulation of ELF objects in a byte ordering and word-size independent way, allowing an application to read and create ELF objects for 32 and 64 bit architectures and for little- and big-endian machines. The library is capable of processing ELF objects that use extended section numbering.

    This manual page serves to provide an overview of the functionality in the ELF library. Further information may found in the manual pages for individual ELF(3) functions that comprise the library.  

    ELF Concepts

    As described in elf(5), ELF files contain several data structures that are laid out in a specific way. ELF files begin with an ``Executable Header'' and may contain an optional ``Program Header Table'' and optional data in the form of ELF ``sections'' A ``Section Header Table'' describes the content of the data in these sections.

    ELF objects have an associated ``ELF class'' which denotes the natural machine word size for the architecture the object is associated with. Objects for 32 bit architectures have an ELF class of ELFCLASS32 Objects for 64 bit architectures have an ELF class of ELFCLASS64

    ELF objects also have an associated ``endianness'' which denotes the endianness of the machine architecture associated with the object. This may be ELFDATA2LSB for little-endian architectures and ELFDATA2MSB for big-endian architectures.

    ELF objects are also associated with an API version number. This version number determines the layout of the individual components of an ELF file and the semantics associated with these.  

    Data Representation And Translation

    The ELF(3) library distinguishes between ``native'' representations of ELF data structures and their ``file'' representations.

    An application would work with ELF data in its ``native'' representation, i.e., using the native byteorder and alignment mandated by the processor the application is running on. The ``file'' representation of the same data could use a different byte ordering and follow different constraints on object alignment than these native constraints.

    Accordingly, the ELF(3) library offers translation facilities (elf32_xlatetof3, elf32_xlatetom3, elf64_xlatetof3 and elf64_xlatetom3) to and from these representations and also provides higher-level APIs that retrieve and store data from the ELF object in a transparent manner.  

    Library Working Version

    Conceptually, there are three version numbers associated with an application using the ELF library to manipulate ELF objects:

    In order to facilitate working with ELF objects of differing versions, the ELF library requires the application to call the elf_version ();
    function before invoking many of its operations, in order to inform the library of the application's desired working version.

    In the current implementation, all three versions have to be EV_CURRENT  

    Namespace use

    The ELF library uses the following prefixes:

    elf_*
    Used for class-independent functions.
    elf32_*
    Used for functions working with 32 bit ELF objects.
    elf64_*
    Used for functions working with 64 bit ELF objects.
    Elf_*
    Used for class-independent data types.
    ELF_C_*
    Used for command values used in a few functions. These symbols are defined as members of the Vt Elf_Cmd enumeration.
    ELF_E_*
    Used for error numbers.
    ELF_F_*
    Used for flags.
    ELF_K_*
    These constants define the kind of file associated with an ELF descriptor. See elf_kind3. The symbols are defined by the Vt Elf_Kind enumeration.
    ELF_T_*
    These values are defined by the Vt Elf_Type enumeration, and denote the types of ELF data structures that can be present in an ELF object.

     

    Descriptors

    Applications communicate with the library using descriptors. These are:

    Vt Elf
    An Vt Elf descriptor represents an ELF object or an ar(1) archive. It is allocated using one of the elf_begin ();
    or elf_memory ();
    functions. An Vt Elf descriptor can be used to read and write data to an ELF file. An Vt Elf descriptor can be associated with zero or more Vt Elf_Scn section descriptors.

    Given an ELF descriptor, the application may retrieve the ELF object's class-dependent ``Executable Header'' structures using the elf32_getehdr ();
    or elf64_getehdr ();
    functions. A new Ehdr structure may be allocated using the elf64_newehdr ();
    or elf64_newehdr ();
    functions.

    The ``Program Header Table'' associated with an ELF descriptor may be allocated using the elf32_getphdr ();
    or elf64_getphdr ();
    functions. A new program header table may be allocated or an existing table resized using the elf32_newphdr ();
    or elf64_newphdr ();
    functions.

    The Vt Elf structure is opaque and has no members visible to the application.

    Vt Elf_Data
    An Vt Elf_Data data structure describes an individual chunk of a ELF file as represented in memory. It has the following application visible members:

    Vt uint64_t d_align
    The in-file alignment of the data buffer within its containing ELF section. This value must be a power of two.
    Vt uint64_t d_off
    The offset with the containing section where this descriptors data would be placed. This field will be computed by the library unless the application requests full control of the ELF object's layout.
    Vt uint64_t d_size
    The number of bytes of data in this descriptor.
    Vt void *d_buf
    A pointer to data in memory.
    Vt Elf_Type d_type
    The ELF type (see below) of the data in this descriptor.
    Vt unsigned int d_version
    The operating version for the data in this buffer.

    Vt Elf_Data descriptors are usually associated with Vt Elf_Scn descriptors. Existing data descriptors associated with an ELF section may be structures are retrieved using the elf_getdata ();
    function. The elf_newdata ();
    function may be used to attach new data descriptors to an ELF section.

    Vt Elf_Scn
    Vt Elf_Scn descriptors represent a section in an ELF object.

    They are retrieved using the elf_getscn ();
    function. An application may iterate through the existing sections of an ELF object using the elf_nextscn ();
    function. New sections may be allocated using the elf_newscn ();
    function.

    The Vt Elf_Scn descriptor is opaque and contains no application modifiable fields.

     

    Supported Elf Types

    The following ELF datatypes are supported by the library.

    ELF_T_ADDR
    Machine addresses.
    ELF_T_BYTE
    Byte data. The library will not attempt to translate byte data.
    ELF_T_CAP
    Software and hardware capability records.
    ELF_T_DYN
    Records used in a section of type SHT_DYNAMIC
    ELF_T_EHDR
    ELF executable header.
    ELF_T_HALF
    16-bit unsigned words.
    ELF_T_LWORD
    64 bit unsigned words.
    ELF_T_MOVE
    ELF Move records.
    ELF_T_NOTE
    ELF Note structures.
    ELF_T_OFF
    File offsets.
    ELF_T_PHDR
    ELF program header table entries.
    ELF_T_REL
    ELF relocation entries.
    ELF_T_RELA
    ELF relocation entries with addends.
    ELF_T_SHDR
    ELF section header entries.
    ELF_T_SWORD
    Signed 32-bit words.
    ELF_T_SXWORD
    Signed 64-bit words.
    ELF_T_SYMINFO
    ELF symbol information.
    ELF_T_SYM
    ELF symbol table entries.
    ELF_T_VDEF
    Symbol version definition records.
    ELF_T_VNEED
    Symbol version requirement records.
    ELF_T_WORD
    Unsigned 32-bit words.
    ELF_T_XWORD
    Unsigned 64-bit words.

    The symbol ELF_T_NUM denotes the number of Elf types known to the library.

    The following table shows the mapping between ELF section types defined in elf(5) and the types supported by the library.

    Section Type Ta Library Type Ta Description
    SHT_DYNAMIC Ta ELF_T_DYN Ta `.dynamic'
    section entries.
    SHT_DYNSYM Ta ELF_T_SYM Ta Symbols for dynamic linking.
    SHT_FINI_ARRAY Ta ELF_T_ADDR Ta Termination function pointers.
    SHT_GROUP Ta ELF_T_WORD Ta Section group marker.
    SHT_HASH Ta ELF_T_HASH Ta Symbol hashes.
    SHT_INIT_ARRAY Ta ELF_T_ADDR Ta Initialization function pointers.
    SHT_NOBITS Ta ELF_T_BYTE Ta
    Empty sections. See elf(5).
    SHT_NOTE Ta ELF_T_NOTE Ta ELF note records.
    SHT_PREINIT_ARRAY Ta ELF_T_ADDR Ta Pre-initialization function pointers.
    SHT_PROGBITS Ta ELF_T_BYTE Ta Machine code.
    SHT_REL Ta ELF_T_REL Ta ELF relocation records.
    SHT_RELA Ta ELF_T_RELA Ta Relocation records with addends.
    SHT_STRTAB Ta ELF_T_BYTE Ta String tables.
    SHT_SYMTAB Ta ELF_T_SYM Ta Symbol tables.
    SHT_SYMTAB_SHNDX Ta ELF_T_WORD Ta Used with extended section numbering.
    SHT_GNU_verdef Ta ELF_T_VDEF Ta Symbol version definitions.
    SHT_GNU_verneed Ta ELF_T_VNEED Ta Symbol versioning requirements.
    SHT_GNU_versym Ta ELF_T_HALF Ta Version symbols.
    SHT_SUNW_move Ta ELF_T_MOVE Ta ELF move records.
    SHT_SUNW_syminfo Ta ELF_T_SYMINFO Ta Additional symbol flags.

     

    Functional Grouping

    This section contains a brief overview of the available functionality in the ELF library. Each function listed here is described further in its own manual page.

    "Archive Access"

    Fn elf_getarsym
    Retrieve the archive symbol table.
    Fn elf_getarhdr
    Retrieve the archive header for an object.
    Fn elf_getbase
    Retrieve the offset of a member inside an archive.
    Fn elf_next
    Iterate through an ar(1) archive.
    Fn elf_rand
    Random access inside an ar(1) archive.

    "Data Structures"

    Fn elf_getdata
    Retrieve translated data for an ELF section.
    Fn elf_getscn
    Retrieve the section descriptor for a named section.
    Fn elf_ndxscn
    Retrieve the index for a section.
    Fn elf_newdata
    Add a new Vt Elf_Data descriptor to an ELF section.
    Fn elf_newscn
    Add a new section descriptor to an ELF descriptor.
    Fn elf_nextscn
    Iterate through the sections in an ELF object.
    Fn elf_rawdata
    Retrieve untranslated data for an ELF sectino.
    Fn elf_rawfile
    Return a pointer to the untranslated file contents for an ELF object.
    Fn elf32_getehdr , Fn elf64_getehdr
    Retrieve the Executable Header in an ELF object.
    Fn elf32_getphdr , Fn elf64_getphdr
    Retrieve the Program Header Table in an ELF object.
    Fn elf32_getshdr , Fn elf64_getshdr
    Retrieve the ELF section header associated with an Vt Elf_Scn descriptor.
    Fn elf32_newehdr , Fn elf64_newehdr
    Allocate an Executable Header in an ELF object.
    Fn elf32_newphdr , Fn elf64_newphdr
    Allocate or resize the Program Header Table in an ELF object.

    "Data Translation"

    Fn elf32_xlatetof , Fn elf64_xlatetof
    Translate an ELF data structure from its native representation to its file representation.
    Fn elf32_xlatetom , Fn elf64_xlatetom
    Translate an ELF data structure from its file representation to a native representation.

    "Error Reporting"

    Fn elf_errno
    Retrieve the current error.
    Fn elf_errmsg
    Retrieve a human readable description of the current error.

    "Initialization"

    Fn elf_begin
    Opens an ar(1) archive or ELF object given a file descriptor.
    Fn elf_end
    Close an ELF descriptor and release all its resources.
    Fn elf_memory
    Opens an ar(1) archive or ELF object present in a memory arena.
    Fn elf_version
    Sets the operating version.

    "IO Control"

    Fn elf_cntl
    Manage the association between and ELF descriptor and its underlying file.
    Fn elf_flagdata
    Mark an Vt Elf_Data descriptor as dirty.
    Fn elf_flagehdr
    Mark the ELF Executable Header in an ELF descriptor as dirty.
    Fn elf_flagphdr
    Mark the ELF Program Header Table in an ELF descriptor as dirty.
    Fn elf_flagscn
    Mark an Vt Elf_Scn descriptor as dirty.
    Fn elf_flagshdr
    Mark an ELF Section Header as dirty.
    Fn elf_setshstrndx
    Set the index of the section name string table for the ELF object.
    Fn elf_update
    Recompute ELF object layout and optionally write the modified object back to the underlying file.

    "Queries"

    Fn elf32_checksum , Fn elf64_checkum
    Compute checksum of an ELF object.
    Fn elf_getident
    Retrieve the identification bytes for an ELF object.
    Fn elf_getshnum
    Retrieve the number of sections in an ELF object.
    Fn elf_getshstrndx
    Retrieve the section index of the section name string table in an ELF object.
    Fn elf_hash
    Compute the ELF hash value of a string.
    Fn elf_kind
    Query the kind of object associated with an ELF descriptor.
    Fn elf32_fsize , Fn elf64_fsize
    Return the size of the file representation of an ELF type.

     

    Controlling ELF Object Layout

    In the usual mode of operation, library will compute section offsets and alignments based on the contents of an ELF descriptor's sections without need for further intervention by the application.

    However, if the application wishes to take complete charge of the layout of the ELF file, it may set the ELF_F_LAYOUT flag on an ELF descriptor using elf_flagelf3, following which the library will use the data offsets and alignments specified by the application when laying out the file.

    Gaps in between sections will be filled with the fill character set by function elf_fill (.);
     

    Error Handling

    In case an error is encountered, these library functions set an internal error number and signal the presence of the error by returning an special return value. The application can check the current error number by calling elf_errno3. A human readable description of the recorded error is available by calling elf_errmsg3.  

    Memory Management Rules

    The library keeps track of all Vt Elf_Scn and Vt Elf_Data descriptors associated with an ELF descriptor and recovers them when the descriptor is closed using elf_end3. Thus the application must not call free(3) on data structures allocated by the ELF library.

    Conversely the library will not free data that it has not allocated. As an example, an application may call elf_newdata3 to allocate a new Vt Elf_Data descriptor and can set the d_off member of the descriptor to point to a region of memory allocated using malloc(3). It is the applications responsibility to free this arena, though the library will reclaim the space used by the Vt Elf_Data descriptor itself.  

    SEE ALSO

    gelf(3), elf(5)  

    HISTORY

    The original ELF(3) API was developed for Unix System V. The current implementation of the ELF(3) API appeared in Fx 7.0 .  

    AUTHORS

    The ELF library was written by An Joseph Koshy Aq jkoshy@FreeBSD.org .


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    ELF Concepts
    Data Representation And Translation
    Library Working Version
    Namespace use
    Descriptors
    Supported Elf Types
    Functional Grouping
    Controlling ELF Object Layout
    Error Handling
    Memory Management Rules
    SEE ALSO
    HISTORY
    AUTHORS


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