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.\" $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