IABSD.fr/src/lib/libelf/elf.3

Branch : - branch - master - tag -

• Show log

  Commit

• Author : jsg
  Date : 2020-05-18 06:46:23
  Hash : 63b93652
  Message : update libelf from elftoolchain r3717 to r3833 ok deraadt@

• lib/libelf/elf.3

• .\" Copyright (c) 2006-2008,2011,2019 Joseph Koshy.  All rights reserved.
  .\"
  .\" Redistribution and use in source and binary forms, with or without
  .\" modification, are permitted provided that the following conditions
  .\" are met:
  .\" 1. Redistributions of source code must retain the above copyright
  .\"    notice, this list of conditions and the following disclaimer.
  .\" 2. Redistributions in binary form must reproduce the above copyright
  .\"    notice, this list of conditions and the following disclaimer in the
  .\"    documentation and/or other materials provided with the distribution.
  .\"
  .\" This software is provided by Joseph Koshy ``as is'' and
  .\" any express or implied warranties, including, but not limited to, the
  .\" implied warranties of merchantability and fitness for a particular purpose
  .\" are disclaimed.  in no event shall Joseph Koshy be liable
  .\" for any direct, indirect, incidental, special, exemplary, or consequential
  .\" damages (including, but not limited to, procurement of substitute goods
  .\" or services; loss of use, data, or profits; or business interruption)
  .\" however caused and on any theory of liability, whether in contract, strict
  .\" liability, or tort (including negligence or otherwise) arising in any way
  .\" out of the use of this software, even if advised of the possibility of
  .\" such damage.
  .\"
  .\" $Id: elf.3,v 1.5 2020/05/18 06:46:23 jsg Exp $
  .\"
  .Dd June 12, 2019
  .Dt ELF 3
  .Os
  .Sh NAME
  .Nm elf
  .Nd API for manipulating ELF objects
  .Sh LIBRARY
  .Lb libelf
  .Sh SYNOPSIS
  .In libelf.h
  .Sh DESCRIPTION
  The
  .Lb libelf
  provides functions that allow an application to read and manipulate
  ELF object files, and to read
  .Xr 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.
  .Pp
  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
  .Fn *elf*
  functions that comprise the library.
  .Ss ELF Concepts
  As described in
  .Xr elf 5 ,
  ELF files contain several data structures that are laid out in a
  specific way.
  ELF files begin with an
  .Dq Executable Header ,
  and may contain an optional
  .Dq Program Header Table ,
  and optional data in the form of ELF
  .Dq sections .
  A
  .Dq Section Header Table
  describes the content of the data in these sections.
  .Pp
  ELF objects have an associated
  .Dq "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
  .Dv ELFCLASS32 .
  Objects for 64 bit architectures have an ELF class of
  .Dv ELFCLASS64 .
  .Pp
  ELF objects also have an associated
  .Dq endianness
  which denotes the endianness of the machine architecture associated
  with the object.
  This may be
  .Dv ELFDATA2LSB
  for little-endian architectures and
  .Dv ELFDATA2MSB
  for big-endian architectures.
  .Pp
  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.
  .Ss Data Representation And Translation
  The
  .Nm
  library distinguishes between
  .Dq native
  representations of ELF data structures and their
  .Dq file
  representations.
  .Pp
  An application would work with ELF data in its
  .Dq native
  representation, i.e., using the native byteorder and alignment mandated
  by the processor the application is running on.
  The
  .Dq file
  representation of the same data could use a different byte ordering
  and follow different constraints on object alignment than these native
  constraints.
  .Pp
  Accordingly, the
  .Nm
  library offers translation facilities
  .Xr ( elf32_xlatetof 3 ,
  .Xr elf32_xlatetom 3 ,
  .Xr elf64_xlatetof 3
  and
  .Xr elf64_xlatetom 3 )
  to and from these representations.
  It also provides higher-level APIs
  .Xr ( gelf_xlatetof 3 ,
  .Xr gelf_xlatetom 3 )
  that retrieve and store data from the ELF object in a class-agnostic
  manner.
  .Ss Library Working Version
  Conceptually, there are three version numbers associated with an
  application using the ELF library to manipulate ELF objects:
  .Bl -bullet -compact -offset indent
  .It
  The ELF version that the application was compiled against.
  This version determines the ABI expected by the application.
  .It
  The ELF version of the ELF object being manipulated by the
  application through the ELF library.
  .It
  The ELF version (or set of versions) supported by the ELF library itself.
  .El
  .Pp
  In order to facilitate working with ELF objects of differing versions,
  the ELF library requires the application to call the
  .Fn elf_version
  function before invoking many of its operations, in order to inform
  the library of the application's desired working version.
  .Pp
  In the current implementation, all three versions have to be
  .Dv EV_CURRENT .
  .Ss Namespace use
  The ELF library uses the following prefixes:
  .Bl -tag -width "ELF_F_*"
  .It Dv elf_
  Used for class-independent functions.
  .It Dv elf32_
  Used for functions working with 32 bit ELF objects.
  .It Dv elf64_
  Used for functions working with 64 bit ELF objects.
  .It Dv Elf_
  Used for class-independent data types.
  .It Dv ELF_C_
  Used for command values used in a few functions.
  These symbols are defined as members of the
  .Vt Elf_Cmd
  enumeration.
  .It Dv ELF_E_
  Used for error numbers.
  .It Dv ELF_F_
  Used for flags.
  .It Dv ELF_K_
  These constants define the kind of file associated with an ELF
  descriptor.
  See
  .Xr elf_kind 3 .
  The symbols are defined by the
  .Vt Elf_Kind
  enumeration.
  .It Dv 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.
  .El
  .Pp
  In addition, the library uses symbols with prefixes
  .Dv _ELF
  and
  .Dv _libelf
  for its internal use.
  .Ss Descriptors
  Applications communicate with the library using descriptors.
  These are:
  .Bl -tag -width ".Vt Elf_Data"
  .It Vt Elf
  An
  .Vt Elf
  descriptor represents an ELF object or an
  .Xr ar 1
  archive.
  It is allocated using one of the
  .Fn elf_begin
  or
  .Fn 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.
  .Pp
  Given an ELF descriptor, the application may retrieve the ELF
  object's class-dependent
  .Dq "Executable Header"
  structures using the
  .Fn elf32_getehdr
  or
  .Fn elf64_getehdr
  functions.
  A new Ehdr structure may be allocated using the
  .Fn elf64_newehdr
  or
  .Fn elf64_newehdr
  functions.
  .Pp
  The
  .Dq "Program Header Table"
  associated with an ELF descriptor may be allocated using the
  .Fn elf32_getphdr
  or
  .Fn elf64_getphdr
  functions.
  A new program header table may be allocated or an existing table
  resized using the
  .Fn elf32_newphdr
  or
  .Fn elf64_newphdr
  functions.
  .Pp
  The
  .Vt Elf
  structure is opaque and has no members visible to the
  application.
  .It 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:
  .Bl -tag -width ".Vt unsigned int d_version" -compact
  .It Vt "uint64_t d_align"
  The in-file alignment of the data buffer within its containing ELF section.
  This value must be non-zero and a power of two.
  .It Vt "void *d_buf"
  A pointer to data in memory.
  .It Vt "uint64_t d_off"
  The offset within the containing section where this descriptor's data
  would be placed.
  This field will be computed by the library unless the application
  requests full control of the ELF object's layout.
  .It Vt "uint64_t d_size"
  The number of bytes of data in this descriptor.
  .It Vt "Elf_Type d_type"
  The ELF type (see below) of the data in this descriptor.
  .It Vt "unsigned int d_version"
  The operating version for the data in this buffer.
  .El
  .Pp
  .Vt Elf_Data
  descriptors are usually used in conjunction with
  .Vt Elf_Scn
  descriptors.
  .It Vt Elf_Scn
  .Vt Elf_Scn
  descriptors represent sections in an ELF object.
  These descriptors are opaque and contain no application modifiable
  fields.
  .Pp
  The
  .Vt Elf_Scn
  descriptor for a specific section in an ELF object can be
  retrieved using the
  .Fn elf_getscn
  function.
  The sections contained in an ELF object can be traversed using the
  .Fn elf_nextscn
  function.
  New sections are allocated using the
  .Fn elf_newscn
  function.
  .Pp
  The
  .Vt Elf_Data
  descriptors associated with a given section can be retrieved
  using the
  .Fn elf_getdata
  function.
  New data descriptors can be added to a section
  descriptor using the
  .Fn elf_newdata
  function.
  The untranslated
  .Dq file
  representation of data in a section can be retrieved using the
  .Fn elf_rawdata
  function.
  .El
  .Ss Supported Elf Types
  The following ELF datatypes are supported by the library.
  .Pp
  .Bl -tag -width ".Dv ELF_T_SYMINFO" -compact
  .It Dv ELF_T_ADDR
  Machine addresses.
  .It Dv ELF_T_BYTE
  Byte data.
  The library will not attempt to translate byte data.
  .It Dv ELF_T_CAP
  Software and hardware capability records.
  .It Dv ELF_T_DYN
  Records used in a section of type
  .Dv SHT_DYNAMIC .
  .It Dv ELF_T_EHDR
  ELF executable header.
  .It Dv ELF_T_GNUHASH
  GNU-style hash tables.
  .It Dv ELF_T_HALF
  16-bit unsigned words.
  .It Dv ELF_T_LWORD
  64 bit unsigned words.
  .It Dv ELF_T_MOVE
  ELF Move records.
  .\".It Dv ELF_T_MOVEP
  .\" As yet unsupported.
  .It Dv ELF_T_NOTE
  ELF Note structures.
  .It Dv ELF_T_OFF
  File offsets.
  .It Dv ELF_T_PHDR
  ELF program header table entries.
  .It Dv ELF_T_REL
  ELF relocation entries.
  .It Dv ELF_T_RELA
  ELF relocation entries with addends.
  .It Dv ELF_T_SHDR
  ELF section header entries.
  .It Dv ELF_T_SWORD
  Signed 32-bit words.
  .It Dv ELF_T_SXWORD
  Signed 64-bit words.
  .It Dv ELF_T_SYMINFO
  ELF symbol information.
  .It Dv ELF_T_SYM
  ELF symbol table entries.
  .It Dv ELF_T_VDEF
  Symbol version definition records.
  .It Dv ELF_T_VNEED
  Symbol version requirement records.
  .It Dv ELF_T_WORD
  Unsigned 32-bit words.
  .It Dv ELF_T_XWORD
  Unsigned 64-bit words.
  .El
  .Pp
  The symbol
  .Dv ELF_T_NUM
  denotes the number of Elf types known to the library.
  .Pp
  The following table shows the mapping between ELF section types
  defined in
  .Xr elf 5
  and the types supported by the library.
  .Bl -column ".Dv SHT_PREINIT_ARRAY" ".Dv ELF_T_SYMINFO"
  .It Em Section Type Ta Em "Library Type" Ta Em Description
  .It Dv SHT_DYNAMIC Ta Dv ELF_T_DYN Ta Xo
  .Sq .dynamic
  section entries.
  .Xc
  .It Dv SHT_DYNSYM Ta Dv ELF_T_SYM Ta Symbols for dynamic linking.
  .It Dv SHT_FINI_ARRAY Ta Dv ELF_T_ADDR Ta Termination function pointers.
  .It Dv SHT_GNU_HASH Ta Dv ELF_T_GNUHASH Ta GNU hash sections.
  .It Dv SHT_GNU_LIBLIST Ta Dv ELF_T_WORD Ta List of libraries to be pre-linked.
  .It Dv SHT_GNU_verdef Ta Dv ELF_T_VDEF Ta Symbol version definitions.
  .It Dv SHT_GNU_verneed Ta Dv ELF_T_VNEED Ta Symbol versioning requirements.
  .It Dv SHT_GNU_versym Ta Dv ELF_T_HALF Ta Version symbols.
  .It Dv SHT_GROUP Ta Dv ELF_T_WORD Ta Section group marker.
  .It Dv SHT_HASH Ta Dv ELF_T_HASH Ta Symbol hashes.
  .It Dv SHT_INIT_ARRAY Ta Dv ELF_T_ADDR Ta Initialization function pointers.
  .It Dv SHT_NOBITS Ta Dv ELF_T_BYTE Ta Xo
  Empty sections.
  See
  .Xr elf 5 .
  .Xc
  .It Dv SHT_NOTE Ta Dv ELF_T_NOTE Ta ELF note records.
  .It Dv SHT_PREINIT_ARRAY Ta Dv ELF_T_ADDR Ta Pre-initialization function pointers.
  .It Dv SHT_PROGBITS Ta Dv ELF_T_BYTE Ta Machine code.
  .It Dv SHT_REL Ta Dv ELF_T_REL Ta ELF relocation records.
  .It Dv SHT_RELA Ta Dv ELF_T_RELA Ta Relocation records with addends.
  .It Dv SHT_STRTAB Ta Dv ELF_T_BYTE Ta String tables.
  .It Dv SHT_SYMTAB Ta Dv ELF_T_SYM Ta Symbol tables.
  .It Dv SHT_SYMTAB_SHNDX Ta Dv ELF_T_WORD Ta Used with extended section numbering.
  .It Dv SHT_SUNW_dof Ta Dv ELF_T_BYTE Ta Xo
  Used by
  .Xr dtrace 1 .
  .Xc
  .It Dv SHT_SUNW_move Ta Dv ELF_T_MOVE Ta ELF move records.
  .It Dv SHT_SUNW_syminfo Ta Dv ELF_T_SYMINFO Ta Additional symbol flags.
  .It Dv SHT_SUNW_verdef Ta Dv ELF_T_VDEF Ta Xo
  Same as
  .Dv SHT_GNU_verdef .
  .Xc
  .It Dv SHT_SUNW_verneed Ta Dv ELF_T_VNEED Ta Xo
  Same as
  .Dv SHT_GNU_verneed .
  .Xc
  .It Dv SHT_SUNW_versym Ta Dv ELF_T_HALF Ta Xo
  Same as
  .Dv SHT_GNU_versym .
  .Xc
  .El
  .Pp
  Section types in the range
  .Dv [ SHT_LOOS ,
  .Dv SHT_HIUSER ]
  are otherwise considered to be of type
  .Dv ELF_T_BYTE .
  .Ss 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.
  .Bl -tag -width indent
  .It "Archive Access"
  .Bl -tag -compact -width indent
  .It Fn elf_getarsym
  Retrieve the archive symbol table.
  .It Fn elf_getarhdr
  Retrieve the archive header for an object.
  .It Fn elf_getbase
  Retrieve the offset of a member inside an archive.
  .It Fn elf_next
  Iterate through an
  .Xr ar 1
  archive.
  .It Fn elf_rand
  Random access inside an
  .Xr ar 1
  archive.
  .El
  .It "Data Structures"
  .Bl -tag -compact -width indent
  .It Fn elf_getdata
  Retrieve translated data for an ELF section.
  .It Fn elf_getscn
  Retrieve the section descriptor for a named section.
  .It Fn elf_ndxscn
  Retrieve the index for a section.
  .It Fn elf_newdata
  Add a new
  .Vt Elf_Data
  descriptor to an ELF section.
  .It Fn elf_newscn
  Add a new section descriptor to an ELF descriptor.
  .It Fn elf_nextscn
  Iterate through the sections in an ELF object.
  .It Fn elf_rawdata
  Retrieve untranslated data for an ELF section.
  .It Fn elf_rawfile
  Return a pointer to the untranslated file contents for an ELF object.
  .It Fn elf32_getehdr , Fn elf64_getehdr
  Retrieve the Executable Header in an ELF object.
  .It Fn elf32_getphdr , Fn elf64_getphdr
  Retrieve the Program Header Table in an ELF object.
  .It Fn elf32_getshdr , Fn elf64_getshdr
  Retrieve the ELF section header associated with an
  .Vt Elf_Scn
  descriptor.
  .It Fn elf32_newehdr , Fn elf64_newehdr
  Allocate an Executable Header in an ELF object.
  .It Fn elf32_newphdr , Fn elf64_newphdr
  Allocate or resize the Program Header Table in an ELF object.
  .El
  .It "Data Translation"
  .Bl -tag -compact -width indent
  .It Fn elf32_xlatetof , Fn elf64_xlatetof
  Translate an ELF data structure from its native representation to its
  file representation.
  .It Fn elf32_xlatetom , Fn elf64_xlatetom
  Translate an ELF data structure from its file representation to a
  native representation.
  .El
  .It "Error Reporting"
  .Bl -tag -compact -width indent
  .It Fn elf_errno
  Retrieve the current error.
  .It Fn elf_errmsg
  Retrieve a human readable description of the current error.
  .El
  .It "Initialization"
  .Bl -tag -compact -width indent
  .It Fn elf_begin
  Opens an
  .Xr ar 1
  archive or ELF object given a file descriptor.
  .It Fn elf_end
  Close an ELF descriptor and release all its resources.
  .It Fn elf_memory
  Opens an
  .Xr ar 1
  archive or ELF object present in a memory arena.
  .It Fn elf_version
  Sets the operating version.
  .El
  .It "IO Control"
  .Bl -tag -width ".Fn elf_setshstrndx" -compact
  .It Fn elf_cntl
  Manage the association between and ELF descriptor and its underlying file.
  .It Fn elf_flagdata
  Mark an
  .Vt Elf_Data
  descriptor as dirty.
  .It Fn elf_flagehdr
  Mark the ELF Executable Header in an ELF descriptor as dirty.
  .It Fn elf_flagphdr
  Mark the ELF Program Header Table in an ELF descriptor as dirty.
  .It Fn elf_flagscn
  Mark an
  .Vt Elf_Scn
  descriptor as dirty.
  .It Fn elf_flagshdr
  Mark an ELF Section Header as dirty.
  .It Fn elf_setshstrndx
  Set the index of the section name string table for the ELF object.
  .It Fn elf_update
  Recompute ELF object layout and optionally write the modified object
  back to the underlying file.
  .El
  .It "Queries"
  .Bl -tag -width ".Fn elf_getshstrndx" -compact
  .It Fn elf32_checksum , Fn elf64_checkum
  Compute checksum of an ELF object.
  .It Fn elf_getident
  Retrieve the identification bytes for an ELF object.
  .It Fn elf_getphdrnum
  Retrieve the number of program headers in an ELF object.
  .It Fn elf_getshdrnum
  Retrieve the number of sections in an ELF object.
  .It Fn elf_getshdrstrndx
  Retrieve the section index of the section name string table in
  an ELF object.
  .It Fn elf_hash
  Compute the ELF hash value of a string.
  .It Fn elf_kind
  Query the kind of object associated with an ELF descriptor.
  .It Fn elf32_fsize , Fn elf64_fsize
  Return the size of the file representation of an ELF type.
  .El
  .El
  .Ss 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.
  .Pp
  However, if the application wishes to take complete charge of the
  layout of the ELF file, it may set the
  .Dv ELF_F_LAYOUT
  flag on an ELF descriptor using
  .Xr elf_flagelf 3 ,
  following which the library will use the data offsets and alignments
  specified by the application when laying out the file.
  Application control of file layout is described further in the
  .Xr elf_update 3
  manual page.
  .Pp
  Gaps in between sections will be filled with the fill character
  set by function
  .Fn elf_fill .
  .Ss 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
  .Xr elf_errno 3 .
  A human readable description of the recorded error is available by
  calling
  .Xr elf_errmsg 3 .
  .Ss 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
  .Xr elf_end 3 .
  Thus the application must not call
  .Xr free 3
  on data structures allocated by the ELF library.
  .Pp
  Conversely the library will not
  free data that it has not allocated.
  As an example, an application may call
  .Xr elf_newdata 3
  to allocate a new
  .Vt Elf_Data
  descriptor and can set the
  .Va d_off
  member of the descriptor to point to a region of memory allocated
  using
  .Xr 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.
  .Sh SEE ALSO
  .Xr gelf 3 ,
  .Xr ar 5 ,
  .Xr elf 5
  .Sh HISTORY
  The original
  .Nm
  API was developed for
  .At V .
  The current implementation of the API appeared in
  .Fx 7.0 .
  .Sh AUTHORS
  The ELF library was written by
  .An Joseph Koshy Aq Mt jkoshy@FreeBSD.org .