.\" $NetBSD: elf_begin.3,v 1.1.1.1 2009/12/19 05:43:39 thorpej Exp $ .\" .\" Copyright (c) 2006 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. .\" .\" $FreeBSD: src/lib/libelf/elf_begin.3,v 1.3.10.1.2.1 2009/10/25 01:10:29 kensmith Exp $ .\" .Dd June 21, 2006 .Os .Dt ELF_BEGIN 3 .Sh NAME .Nm elf_begin .Nd open an ELF file or ar(1) archive .Sh LIBRARY .Lb libelf .Sh SYNOPSIS .In libelf.h .Ft "Elf *" .Fn elf_begin "int fd" "Elf_Cmd cmd" "Elf *elf" .Sh DESCRIPTION Function .Fn elf_begin is used to open ELF files and .Xr ar 1 archives for further processing by other APIs in the .Xr elf 3 library. It is also used to access individual ELF members of an .Xr ar 1 archive in combination with the .Xr elf_next 3 and .Xr elf_rand 3 APIs. .Pp Argument .Ar fd is an open file descriptor returned from an .Xr open 2 system call. Function .Fn elf_begin uses argument .Ar fd for reading or writing depending on the value of argument .Ar cmd . Argument .Ar elf is primarily used for iterating through archives. .Pp The argument .Ar cmd can have the following values: .Bl -tag -width "ELF_C_WRITE" .It ELF_C_NULL Causes .Fn elf_begin to return NULL. Arguments .Ar fd and .Ar elf are ignored, and no additional error is signalled. .It ELF_C_READ This value is to be when the application wishes to examine (but not modify) the contents of the file specified by argument .Ar fd . It can be used for both .Xr ar 1 archives and for regular ELF files. .Pp Argument .Ar fd should have been opened for reading. If argument .Ar elf is NULL, the library will allocate a new ELF descriptor for the file being processed. If argument .Ar elf is not NULL, and references a regular ELF file previously opened with .Fn elf_begin , then the activation count for .Ar elf is incremented. If argument .Ar elf is not NULL, and references a descriptor for an .Xr ar 1 archive opened earlier with .Fn elf_begin , a descriptor for an element in the archive is returned as described in the section .Sx "Processing ar(1) archives" below. .It Dv ELF_C_RDWR The command is used to prepare an ELF file for reading and writing. It is not supported for archives. .Pp Argument .Ar fd should have been opened for reading and writing. If argument .Ar elf is NULL, the library will allocate a new ELF descriptor for the file being processed. If the argument .Ar elf is non-null, it should point to a descriptor previously allocated with .Fn elf_begin with the same values for arguments .Ar fd and .Ar cmd ; in this case the library will increment the activation count for descriptor .Ar elf and return the same descriptor. Changes to the in-memory image of the ELF file are written back to disk using the .Xr elf_update 3 function. .Pp This command is not valid for .Xr ar 1 archives. .It Dv ELF_C_WRITE This command is used when the application wishes to create a new ELF file. Argument .Ar fd should have been opened for writing. Argument .Ar elf is ignored, and the previous contents of file referenced by argument .Ar fd are overwritten. .El .Ss Processing ar(1) archives An .Xr ar 1 archive may be opened in read mode (with argument .Ar cmd set to .Dv ELF_C_READ ) using .Fn elf_begin . The returned ELF descriptor can be passed into to subsequent calls to .Fn elf_begin to access individual members of the archive. .Pp Random access within an opened archive is possible using the .Xr elf_next 3 and .Xr elf_rand 3 functions. .Pp The symbol table of the archive may be retrieved using .Xr elf_getarsym 3 . .Sh RETURN VALUES The function returns a pointer to a ELF descriptor if successful, or NULL if an error occurred. .Sh EXAMPLES To iterate through the members of an .Xr ar 1 archive, use: .Bd -literal -offset indent 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); } .Ed .Pp To create a new ELF file, use: .Bd -literal -offset indent 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); .Ed .Sh ERRORS Function .Fn elf_begin can fail with the following errors: .Pp .Bl -tag -width "[ELF_E_RESOURCE]" .It Bq Er ELF_E_ARGUMENT An unrecognized value was specified in argument .Ar cmd . .It Bq Er ELF_E_ARGUMENT A non-null value for argument .Ar elf was specified when .Ar cmd was set to .Dv ELF_C_RDWR . .It Bq Er ELF_E_ARGUMENT The value of argument .Ar fd differs from the one the ELF descriptor .Ar elf was created with. .It Bq Er ELF_E_ARGUMENT Argument .Ar cmd differs from the value specified when ELF descriptor .Ar elf was created. .It Bq Er ELF_E_ARGUMENT Argument .Ar elf was not a descriptor for an .Xr ar 1 archive. .It Bq Er ELF_E_ARGUMENT An .Xr ar 1 archive was opened with with .Ar cmd set to .Dv ELF_C_RDWR . .It Bq Er ELF_E_IO Function .Fn elf_begin was unable to truncate a file opened for writing using .Dv ELF_C_WRITE . .It Bq Er ELF_E_RESOURCE An out of memory condition was encountered. .It Bq Er ELF_E_SEQUENCE Function .Fn elf_begin was called before a working version was established with .Xr elf_version 3 . .El .Sh SEE ALSO .Xr elf 3 , .Xr elf_end 3 , .Xr elf_errno 3 , .Xr elf_memory 3 , .Xr elf_next 3 , .Xr elf_rand 3 , .Xr elf_update 3 , .Xr gelf 3