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.\" 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: gelf_newehdr.3,v 1.3 2020/05/18 06:46:23 jsg Exp $
.\"
.Dd June 12, 2019
.Dt GELF_NEWEHDR 3
.Os
.Sh NAME
.Nm elf32_newehdr ,
.Nm elf64_newehdr ,
.Nm gelf_newehdr
.Nd retrieve or allocate the object file header
.Sh LIBRARY
.Lb libelf
.Sh SYNOPSIS
.In libelf.h
.Ft "Elf32_Ehdr *"
.Fn elf32_newehdr "Elf *elf"
.Ft "Elf64_Ehdr *"
.Fn elf64_newehdr "Elf *elf"
.In gelf.h
.Ft "void *"
.Fn gelf_newehdr "Elf *elf" "int elfclass"
.Sh DESCRIPTION
These functions retrieve the ELF header from the ELF descriptor
.Ar elf ,
allocating a new header if needed.
File data structures are translated to their in-memory representations
as described in
.Xr elf 3 .
.Pp
Function
.Fn elf32_newehdr
returns a pointer to a 32 bit
.Vt Elf32_Ehdr
structure.
Function
.Fn elf64_newehdr
returns a pointer to a 64 bit
.Vt Elf64_Ehdr
structure.
.Pp
When argument
.Ar elfclass
has value
.Dv ELFCLASS32 ,
function
.Fn gelf_newehdr
returns the value returned by
.Fn elf32_newehdr "elf" .
When argument
.Ar elfclass
has value
.Dv ELFCLASS64
it returns the value returned by
.Fn elf64_newehdr "elf" .
.Pp
If a fresh header structure is allocated, the members of the
structure are initialized as follows:
.Bl -tag -width indent
.It Va "e_ident[EI_MAG0..EI_MAG3]"
Identification bytes at offsets
.Dv EI_MAG0 ,
.Dv EI_MAG1 ,
.Dv EI_MAG2
and
.Dv EI_MAG3
are set to the ELF signature.
.It Va "e_ident[EI_CLASS]"
The identification byte at offset
.Dv EI_CLASS
is set to the ELF class associated with the function being called
or to argument
.Ar elfclass
for function
.Fn gelf_newehdr .
.It Va "e_ident[EI_DATA]"
The identification byte at offset
.Dv EI_DATA
is set to
.Dv ELFDATANONE .
.It Va "e_ident[EI_VERSION]"
The identification byte at offset
.Dv EI_VERSION
is set to the ELF library's operating version set by a prior call to
.Xr elf_version 3 .
.It Va e_machine
is set to
.Dv EM_NONE .
.It Va e_type
is set to
.Dv ELF_K_NONE .
.It Va e_version
is set to the ELF library's operating version set by a prior call to
.Xr elf_version 3 .
.El
.Pp
Other members of the header are set to zero.
The application is responsible for changing these values
as needed before calling
.Fn elf_update .
.Pp
If successful, these three functions set the
.Dv ELF_F_DIRTY
flag on ELF descriptor
.Ar elf .
.Sh RETURN VALUES
These functions return a pointer to a translated header descriptor
if successful, or NULL on failure.
.Sh COMPATIBILITY
The
.Fn gelf_newehdr
function uses a type of
.Ft "void *"
for its returned value.
This differs from some other implementations of the
.Xr elf 3
API, which use an
.Ft "unsigned long"
return type.
.Sh ERRORS
These functions can fail with the following errors:
.Bl -tag -width "[ELF_E_RESOURCE]"
.It Bq Er ELF_E_ARGUMENT
The argument
.Ar elf
was null.
.It Bq Er ELF_E_ARGUMENT
Argument
.Ar elf
was not a descriptor for an ELF object.
.It Bq Er ELF_E_ARGUMENT
Argument
.Ar elfclass
had an unsupported value.
.It Bq Er ELF_E_ARGUMENT
The class of the ELF descriptor
.Ar elf
did not match that of the requested operation.
.It Bq Er ELF_E_ARGUMENT
For function
.Fn gelf_newehdr ,
the class of argument
.Ar elf
was not
.Dv ELFCLASSNONE
and did not match the argument
.Ar elfclass .
.It Bq Er ELF_E_CLASS
The ELF class of descriptor
.Ar elf
did not match that of the API function being called.
.It Bq Er ELF_E_HEADER
A malformed ELF header was detected.
.It Bq Er ELF_E_RESOURCE
An out of memory condition was detected during execution.
.It Bq Er ELF_E_SECTION
The ELF descriptor in argument
.Ar elf
did not adhere to the conventions used for extended numbering.
.It Bq Er ELF_E_VERSION
The ELF descriptor
.Ar elf
had an unsupported ELF version number.
.El
.Sh SEE ALSO
.Xr elf 3 ,
.Xr elf32_getehdr 3 ,
.Xr elf64_getehdr 3 ,
.Xr elf_flagdata 3 ,
.Xr elf_getident 3 ,
.Xr elf_update 3 ,
.Xr elf_version 3 ,
.Xr gelf 3 ,
.Xr gelf_getehdr 3 ,
.Xr elf 5
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