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#include <libelf.h>
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_C_NULL | Causes elf_begin() to return NULL. Arguments fd and elf are ignored, and no additional error is signalled. |
ELF_C_READ |
This value is to be when the application wishes to examine (but not
modify) the contents of the file specified by the arguments
fd
and
elf.
It can be used for both
ar(1)
archives and for ELF objects.
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_RDWR |
This command is used to prepare an ELF file for reading and writing.
This command is not supported for
ar(1)
archives.
Argument 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_WRITE | |
This command is used when the application wishes to create a new ELF file. Argument fd should have been opened for writing. Argument elf is ignored, and the previous contents of file referenced by argument fd are overwritten. | |
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).
Elf_Cmd c; Elf *ar_e, *elf_e; amp;... c = ELF_C_READ; if ((ar_e = elf_begin(fd, c, (Elf *) 0)) == 0) { amp;... handle error in opening the archive ... } while ((elf_e = elf_begin(fd, c, ar_e)) != 0) { amp;... 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; amp;... if ((fd = open("filename", O_RDWR|O_TRUNC|O_CREAT, 0666)) < 0) { amp;... handle the error from open(2) ... } if ((e = elf_begin(fd, ELF_C_WRITE, (Elf *) 0)) == 0) { amp;... handle the error from elf_begin() ... } amp;... create the ELF image using other elf(3) APIs ... elf_update(e, ELF_C_WRITE); elf_end(e);
[ELF_E_ARCHIVE] | The archive denoted by argument elf could not be parsed. |
[ELF_E_ARGUMENT] | |
The value in argument cmd was unrecognized. | |
[ELF_E_ARGUMENT] | |
A non-null value for argument elf was specified when cmd was set to ELF_C_RDWR. | |
[ELF_E_ARGUMENT] | |
The value of argument fd differs from the one the ELF descriptor elf was created with. | |
[ELF_E_ARGUMENT] | |
Argument cmd differs from the value specified when ELF descriptor elf was created. | |
[ELF_E_ARGUMENT] | |
An ar(1) archive was opened with cmd set to ELF_C_RDWR. | |
[ELF_E_ARGUMENT] | |
The file referenced by argument fd was empty. | |
[ELF_E_ARGUMENT] | |
The underlying file for argument fd was of an unsupported type. | |
[ELF_E_IO] | The file descriptor in argument fd was invalid. |
[ELF_E_IO] | The file descriptor in argument fd could not be read or written to. |
[ELF_E_RESOURCE] | |
An out of memory condition was encountered. | |
[ELF_E_SEQUENCE] | |
Function elf_begin() was called before a working version was established with elf_version(3). | |
[ELF_E_VERSION] | The ELF object referenced by argument fd was of an unsupported ELF version. |
ELF_BEGIN (3) | December 11, 2011 |
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