.\"	$NetBSD: elf_getdata.3,v 1.3 2010/01/29 10:49:07 wiz Exp $
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.\" $FreeBSD: src/lib/libelf/elf_getdata.3,v 1.2.10.1.2.1 2009/10/25 01:10:29 kensmith Exp $
.\"
.Dd April 7, 2008
.Os
.Dt ELF_GETDATA 3
.Sh NAME
.Nm elf_getdata ,
.Nm elf_newdata ,
.Nm elf_rawdata
.Nd iterate through or allocate section data
.Sh LIBRARY
.Lb libelf
.Sh SYNOPSIS
.In libelf.h
.Ft "Elf_Data *"
.Fn elf_getdata "Elf_Scn *scn" "Elf_Data *data"
.Ft "Elf_Data *"
.Fn elf_newdata "Elf_Scn *scn"
.Ft "Elf_Data *"
.Fn elf_rawdata "Elf_Scn *scn" "Elf_Data *data"
.Sh DESCRIPTION
These functions are used to access and manipulate data descriptors
associated with section descriptors.
Data descriptors used by the ELF library are described in
.Xr elf 3 .
.Pp
Function
.Fn elf_getdata
will return the next data descriptor associated with section descriptor
.Ar scn .
The returned data descriptor will be setup to contain translated data.
Argument
.Ar data
may be
.Dv NULL ,
in which case the function returns the first data descriptor
associated with section
.Ar scn .
If argument
.Ar data
is not
.Dv NULL ,
it must be a pointer to a data descriptor associated with
section descriptor
.Ar scn ,
and function
.Fn elf_getdata
will return a pointer to the next data descriptor for the section,
or
.Dv NULL
when the end of the section's descriptor list is reached.
.Pp
Function
.Fn elf_newdata
will allocate a new data descriptor and append it to the list of data
descriptors associated with section descriptor
.Ar scn .
The new data descriptor will be initialized as follows:
.Bl -tag -width "d_version" -compact -offset indent
.It Va d_align
Set to 1.
.It Va d_buf
Initialized to
.Dv NULL .
.It Va d_off
Set to (off_t) -1.
This field is under application control if the
.Dv ELF_F_LAYOUT
flag was set on the ELF descriptor.
.It Va d_size
Set to zero.
.It Va d_type
Initialized to
.Dv ELF_T_BYTE .
.It Va d_version
Set to the current working version of the library, as set by
.Xr elf_version 3 .
.El
The application must set these values as appropriate before
calling
.Xr elf_update 3 .
Section
.Ar scn
must be associated with an ELF file opened for writing.
If the application has not requested full control of layout by
setting the
.Dv ELF_F_LAYOUT
flag on descriptor
.Ar elf ,
then the data referenced by the returned descriptor will be positioned
after the existing content of the section, honoring the file alignment
specified in member
.Va d_align .
On successful completion of a call to
.Fn elf_newdata ,
the ELF library will mark the section
.Ar scn
as
.Dq dirty .
.Pp
Function
.Fn elf_rawdata
is used to step through the data descriptors associated with
section
.Ar scn .
In contrast to function
.Fn elf_getdata ,
this function returns untranslated data.
If argument
.Ar data
is
.Dv NULL ,
the first data descriptor associated with section
.Ar scn
is returned.
If argument
.Ar data
is not
.Dv NULL ,
is must be a data descriptor associated with section
.Ar scn ,
and function
.Fn elf_rawdata
will return the next data descriptor in the list, or
.Dv NULL
if no further descriptors are present.
Function
.Fn elf_rawdata
always returns
.Vt Elf_Data
structures of type
.Dv ELF_T_BYTE .
.Ss Special handling of SHT_NOBITS sections
For sections of type
.Dv SHT_NOBITS ,
the functions
.Fn elf_getdata
and
.Fn elf_rawdata
return a pointer to a valid
.Vt Elf_Data
structure that has its
.Va d_buf
member set to
.Dv NULL
and its
.Va d_size
member set to the size of the section.
.Pp
If an application wishes to create a section of type
.Dv SHT_NOBITS ,
it should add a data buffer to the section using function
.Fn elf_newdata .
It should then set the
.Va d_buf
and
.Va d_size
members of the returned
.Vt Elf_Data
structure to
.Dv NULL
and the desired size of the section respectively.
.Sh RETURN VALUES
These functions return a valid pointer to a data descriptor if successful, or
.Dv NULL
if an error occurs.
.Sh ERRORS
These functions may fail with the following errors:
.Bl -tag -width "[ELF_E_RESOURCE]"
.It Bq Er ELF_E_ARGUMENT
Arguments
.Ar scn
was
.Dv NULL ,
or data descriptor
.Ar data
was not associated with section descriptor
.Ar scn .
.It Bq Er ELF_E_RESOURCE
An out of memory condition was detected.
.El
.Sh SEE ALSO
.Xr elf 3 ,
.Xr elf_flagdata 3 ,
.Xr elf_flagscn 3 ,
.Xr elf_getscn 3 ,
.Xr elf_getshdr 3 ,
.Xr elf_newscn 3 ,
.Xr elf_update 3 ,
.Xr elf_version 3 ,
.Xr gelf 3