281 lines
6.5 KiB
Groff
281 lines
6.5 KiB
Groff
.\" Copyright (c) 2006,2008 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.
|
|
.\"
|
|
.\" $Id$
|
|
.\"
|
|
.Dd April 11, 2010
|
|
.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
|
|
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
|
|
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
|
|
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
|