| ELF_BEGIN(3) | Library Functions Manual | ELF_BEGIN(3) | 
elf_begin —
#include <libelf.h>
Elf *
  
  elf_begin(int
    fd, Elf_Cmd cmd,
    Elf *elf);
elf_begin() is used to open ELF files and
  ar(1) archives for further
  processing by other APIs in the
  elf(3) library. It is also used to
  access individual ELF members of an
  ar(1) archive in combination with
  the elf_next(3) and
  elf_rand(3) APIs.
Argument fd is an open file descriptor
    returned from an open(2) system
    call. Function elf_begin() uses argument
    fd for reading or writing depending on the value of
    argument cmd. Argument elf is
    primarily used for iterating through archives.
The argument cmd can have the following values:
elf_begin() to return
      NULL. Arguments fd and
      elf are ignored, and no additional error is
      signalled.If argument elf is
        NULL, the library will allocate a new ELF
        descriptor for the file being processed. The argument
        fd should have been opened for reading.
If argument elf is not
        NULL, and references a regular ELF file
        previously opened with elf_begin(), then the
        activation count for the descriptor referenced by argument
        elf is incremented. The value in argument
        fd should match that used to open the descriptor
        argument elf.
If argument elf is not
        NULL, and references a descriptor for an
        ar(1) archive opened earlier
        with elf_begin(), a descriptor for an element in
        the archive is returned as described in the section
        Processing ar(1)
        archives below. The value for argument fd
        should match that used to open the archive earlier.
If argument elf is not
        NULL, and references an
        ar(1) archive opened earlier
        with elf_memory(), then the value of the
        argument fd is ignored.
ELF_C_RDWRArgument fd should have been opened for
        reading and writing. If argument elf is
        NULL, the library will allocate a new ELF
        descriptor for the file being processed. If the argument
        elf is non-null, it should point to a descriptor
        previously allocated with elf_begin() with the
        same values for arguments fd and
        cmd; in this case the library will increment the
        activation count for descriptor elf and return the
        same descriptor.
Changes to the in-memory image of the ELF file may be written back to disk using the elf_update(3) function.
ELF_C_WRITEELF_C_READ) using elf_begin()
  or elf_memory(). The returned ELF descriptor can be
  passed into to subsequent calls to elf_begin() to
  access individual members of the archive.
Random access within an opened archive is possible using the elf_next(3) and elf_rand(3) functions.
The symbol table of the archive may be retrieved using elf_getarsym(3).
NULL if an error occurred.
Elf_Cmd c;
Elf *ar_e, *elf_e;
...
c = ELF_C_READ;
if ((ar_e = elf_begin(fd, c, (Elf *) 0)) == 0) {
	... handle error in opening the archive ...
}
while ((elf_e = elf_begin(fd, c, ar_e)) != 0) {
	... process member referenced by elf_e here ...
	c = elf_next(elf_e);
	elf_end(elf_e);
}
To create a new ELF file, use:
int fd;
Elf *e;
...
if ((fd = open("filename", O_RDWR|O_TRUNC|O_CREAT, 0666)) < 0) {
	... handle the error from open(2) ...
}
if ((e = elf_begin(fd, ELF_C_WRITE, (Elf *) 0)) == 0) {
	... handle the error from elf_begin() ...
}
... create the ELF image using other elf(3) APIs ...
elf_update(e, ELF_C_WRITE);
elf_end(e);
elf_begin() can fail with the following errors:
ELF_E_ARCHIVE]ELF_E_ARGUMENT]ELF_E_ARGUMENT]ELF_C_RDWR.ELF_E_ARGUMENT]ELF_E_ARGUMENT]ELF_E_ARGUMENT]ELF_C_RDWR.ELF_E_ARGUMENT]ELF_E_ARGUMENT]ELF_E_IO]ELF_E_IO]ELF_E_RESOURCE]ELF_E_SEQUENCE]elf_begin() was called before a working
      version was established with
      elf_version(3).ELF_E_VERSION]| December 11, 2011 | NetBSD 10.0 |