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Diffstat (limited to 'lib/libelf/elf_begin.3')
| -rw-r--r-- | lib/libelf/elf_begin.3 | 315 |
1 files changed, 315 insertions, 0 deletions
diff --git a/lib/libelf/elf_begin.3 b/lib/libelf/elf_begin.3 new file mode 100644 index 00000000000..9f7515fe22d --- /dev/null +++ b/lib/libelf/elf_begin.3 @@ -0,0 +1,315 @@ +.\" Copyright (c) 2006,2008-2011 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_begin.3,v 1.1 2019/02/01 05:27:37 jsg Exp $ +.\" +.Dd December 11, 2011 +.Dt ELF_BEGIN 3 +.Os +.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 the arguments +.Ar fd +and +.Ar elf . +It can be used for both +.Xr ar 1 +archives and for ELF objects. +.Pp +If argument +.Ar elf +is NULL, the library will allocate a new ELF descriptor for the file +being processed. +The argument +.Ar fd +should have been opened for reading. +.Pp +If argument +.Ar elf +is not NULL, and references a regular ELF file previously opened with +.Fn elf_begin , +then the activation count for the descriptor referenced by argument +.Ar elf +is incremented. +The value in argument +.Ar fd +should match that used to open the descriptor argument +.Ar elf . +.Pp +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. +The value for argument +.Ar fd +should match that used to open the archive earlier. +.Pp +If argument +.Ar elf +is not NULL, and references an +.Xr ar 1 +archive opened earlier with +.Fn elf_memory , +then the value of the argument +.Ar fd +is ignored. +.It Dv ELF_C_RDWR +This command is used to prepare an ELF file for reading and writing. +This command is not supported for +.Xr ar 1 +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. +.Pp +Changes to the in-memory image of the ELF file may be written back to +disk using the +.Xr elf_update 3 +function. +.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 +or +.Fn elf_memory . +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: +.Bl -tag -width "[ELF_E_RESOURCE]" +.It Bq Er ELF_E_ARCHIVE +The archive denoted by argument +.Ar elf +could not be parsed. +.It Bq Er ELF_E_ARGUMENT +The value in argument +.Ar cmd +was unrecognized. +.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 +An +.Xr ar 1 +archive was opened with +.Ar cmd +set to +.Dv ELF_C_RDWR . +.It Bq Er ELF_E_ARGUMENT +The file referenced by argument +.Ar fd +was empty. +.It Bq Er ELF_E_ARGUMENT +The underlying file for argument +.Ar fd +was of an unsupported type. +.It Bq Er ELF_E_IO +The file descriptor in argument +.Ar fd +was invalid. +.It Bq Er ELF_E_IO +The file descriptor in argument +.Ar fd +could not be read or written to. +.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 . +.It Bq Er ELF_E_VERSION +The ELF object referenced by argument +.Ar fd +was of an unsupported ELF version. +.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 |