ae500c1ff8
Highlights: - Make sure that only TLS sections are sorted into TLS segment. - Fixed multiple errors in "Section to Segment mapping". - Man page updates - ar improvements - elfcopy: avoid filter_reloc uninitialized variable for rela - elfcopy: avoid stripping relocations from static binaries - readelf: avoid printing directory in front of absolute path - readelf: add NT_FREEBSD_FEATURE_CTL FreeBSD note type - test improvements NOTES: Some of these changes originated in FreeBSD and simply reduce diffs between contrib and vendor. ELF Tool Chain ar is not (currently) used in FreeBSD, and there are improvements in both FreeBSD and ELF Tool Chain ar that are not in the other. Sponsored by: The FreeBSD Foundation
316 lines
7.2 KiB
Groff
316 lines
7.2 KiB
Groff
.\" Copyright (c) 2006,2008-2011 Joseph Koshy. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" This software is provided by Joseph Koshy ``as is'' and
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.\" any express or implied warranties, including, but not limited to, the
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.\" implied warranties of merchantability and fitness for a particular purpose
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.\" are disclaimed. in no event shall Joseph Koshy be liable
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.\" for any direct, indirect, incidental, special, exemplary, or consequential
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.\" damages (including, but not limited to, procurement of substitute goods
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.\" or services; loss of use, data, or profits; or business interruption)
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.\" however caused and on any theory of liability, whether in contract, strict
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.\" liability, or tort (including negligence or otherwise) arising in any way
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.\" out of the use of this software, even if advised of the possibility of
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.\" such damage.
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.\"
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.\" $Id: elf_begin.3 3639 2018-10-14 14:07:02Z jkoshy $
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.\"
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.Dd December 11, 2011
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.Dt ELF_BEGIN 3
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.Os
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.Sh NAME
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.Nm elf_begin
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.Nd open an ELF file or ar(1) archive
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.Sh LIBRARY
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.Lb libelf
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.Sh SYNOPSIS
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.In libelf.h
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.Ft "Elf *"
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.Fn elf_begin "int fd" "Elf_Cmd cmd" "Elf *elf"
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.Sh DESCRIPTION
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Function
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.Fn elf_begin
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is used to open ELF files and
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.Xr ar 1
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archives for further processing by other APIs in the
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.Xr elf 3
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library.
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It is also used to access individual ELF members of an
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.Xr ar 1
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archive in combination with the
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.Xr elf_next 3
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and
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.Xr elf_rand 3
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APIs.
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.Pp
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Argument
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.Ar fd
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is an open file descriptor returned from an
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.Xr open 2
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system call.
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Function
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.Fn elf_begin
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uses argument
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.Ar fd
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for reading or writing depending on the value of argument
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.Ar cmd .
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Argument
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.Ar elf
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is primarily used for iterating through archives.
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.Pp
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The argument
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.Ar cmd
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can have the following values:
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.Bl -tag -width "ELF_C_WRITE"
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.It ELF_C_NULL
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Causes
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.Fn elf_begin
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to return NULL.
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Arguments
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.Ar fd
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and
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.Ar elf
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are ignored, and no additional error is signalled.
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.It ELF_C_READ
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This value is to be when the application wishes to examine (but not
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modify) the contents of the file specified by the arguments
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.Ar fd
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and
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.Ar elf .
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It can be used for both
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.Xr ar 1
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archives and for ELF objects.
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.Pp
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If argument
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.Ar elf
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is NULL, the library will allocate a new ELF descriptor for the file
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being processed.
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The argument
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.Ar fd
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should have been opened for reading.
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.Pp
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If argument
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.Ar elf
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is not NULL, and references a regular ELF file previously opened with
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.Fn elf_begin ,
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then the activation count for the descriptor referenced by argument
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.Ar elf
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is incremented.
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The value in argument
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.Ar fd
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should match that used to open the descriptor argument
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.Ar elf .
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.Pp
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If argument
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.Ar elf
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is not NULL, and references a descriptor for an
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.Xr ar 1
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archive opened earlier with
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.Fn elf_begin ,
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a descriptor for an element in the archive is returned as
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described in the section
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.Sx "Processing ar(1) archives"
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below.
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The value for argument
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.Ar fd
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should match that used to open the archive earlier.
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.Pp
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If argument
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.Ar elf
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is not NULL, and references an
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.Xr ar 1
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archive opened earlier with
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.Fn elf_memory ,
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then the value of the argument
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.Ar fd
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is ignored.
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.It Dv ELF_C_RDWR
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This command is used to prepare an ELF file for reading and writing.
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This command is not supported for
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.Xr ar 1
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archives.
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.Pp
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Argument
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.Ar fd
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should have been opened for reading and writing.
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If argument
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.Ar elf
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is NULL, the library will allocate a new ELF descriptor for
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the file being processed.
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If the argument
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.Ar elf
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is non-null, it should point to a descriptor previously
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allocated with
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.Fn elf_begin
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with the same values for arguments
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.Ar fd
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and
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.Ar cmd ;
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in this case the library will increment the activation count for descriptor
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.Ar elf
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and return the same descriptor.
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.Pp
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Changes to the in-memory image of the ELF file may be written back to
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disk using the
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.Xr elf_update 3
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function.
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.It Dv ELF_C_WRITE
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This command is used when the application wishes to create a new ELF
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file.
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Argument
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.Ar fd
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should have been opened for writing.
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Argument
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.Ar elf
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is ignored, and the previous contents of file referenced by argument
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.Ar fd
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are overwritten.
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.El
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.Ss Processing ar(1) archives
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An
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.Xr ar 1
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archive may be opened in read mode (with argument
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.Ar cmd
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set to
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.Dv ELF_C_READ )
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using
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.Fn elf_begin
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or
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.Fn elf_memory .
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The returned ELF descriptor can be passed into to
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subsequent calls to
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.Fn elf_begin
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to access individual members of the archive.
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.Pp
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Random access within an opened archive is possible using
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the
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.Xr elf_next 3
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and
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.Xr elf_rand 3
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functions.
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.Pp
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The symbol table of the archive may be retrieved
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using
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.Xr elf_getarsym 3 .
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.Sh RETURN VALUES
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The function returns a pointer to a ELF descriptor if successful, or NULL
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if an error occurred.
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.Sh EXAMPLES
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To iterate through the members of an
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.Xr ar 1
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archive, use:
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.Bd -literal -offset indent
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Elf_Cmd c;
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Elf *ar_e, *elf_e;
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\&...
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c = ELF_C_READ;
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if ((ar_e = elf_begin(fd, c, (Elf *) 0)) == 0) {
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\&... handle error in opening the archive ...
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}
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while ((elf_e = elf_begin(fd, c, ar_e)) != 0) {
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\&... process member referenced by elf_e here ...
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c = elf_next(elf_e);
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elf_end(elf_e);
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}
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.Ed
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.Pp
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To create a new ELF file, use:
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.Bd -literal -offset indent
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int fd;
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Elf *e;
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\&...
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if ((fd = open("filename", O_RDWR|O_TRUNC|O_CREAT, 0666)) < 0) {
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\&... handle the error from open(2) ...
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}
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if ((e = elf_begin(fd, ELF_C_WRITE, (Elf *) 0)) == 0) {
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\&... handle the error from elf_begin() ...
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}
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\&... create the ELF image using other elf(3) APIs ...
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elf_update(e, ELF_C_WRITE);
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elf_end(e);
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.Ed
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.Sh ERRORS
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Function
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.Fn elf_begin
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can fail with the following errors:
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.Bl -tag -width "[ELF_E_RESOURCE]"
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.It Bq Er ELF_E_ARCHIVE
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The archive denoted by argument
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.Ar elf
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could not be parsed.
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.It Bq Er ELF_E_ARGUMENT
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The value in argument
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.Ar cmd
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was unrecognized.
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.It Bq Er ELF_E_ARGUMENT
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A non-null value for argument
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.Ar elf
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was specified when
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.Ar cmd
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was set to
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.Dv ELF_C_RDWR .
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.It Bq Er ELF_E_ARGUMENT
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The value of argument
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.Ar fd
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differs from the one the ELF descriptor
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.Ar elf
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was created with.
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.It Bq Er ELF_E_ARGUMENT
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Argument
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.Ar cmd
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differs from the value specified when ELF descriptor
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.Ar elf
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was created.
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.It Bq Er ELF_E_ARGUMENT
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An
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.Xr ar 1
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archive was opened with
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.Ar cmd
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set to
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.Dv ELF_C_RDWR .
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.It Bq Er ELF_E_ARGUMENT
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The file referenced by argument
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.Ar fd
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was empty.
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.It Bq Er ELF_E_ARGUMENT
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The underlying file for argument
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.Ar fd
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was of an unsupported type.
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.It Bq Er ELF_E_IO
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The file descriptor in argument
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.Ar fd
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was invalid.
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.It Bq Er ELF_E_IO
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The file descriptor in argument
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.Ar fd
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could not be read or written to.
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.It Bq Er ELF_E_RESOURCE
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An out of memory condition was encountered.
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.It Bq Er ELF_E_SEQUENCE
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Function
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.Fn elf_begin
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was called before a working version was established with
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.Xr elf_version 3 .
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.It Bq Er ELF_E_VERSION
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The ELF object referenced by argument
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.Ar fd
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was of an unsupported ELF version.
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.El
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.Sh SEE ALSO
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.Xr elf 3 ,
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.Xr elf_end 3 ,
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.Xr elf_errno 3 ,
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.Xr elf_memory 3 ,
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.Xr elf_next 3 ,
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.Xr elf_rand 3 ,
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.Xr elf_update 3 ,
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.Xr gelf 3
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