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.\" $Id: gelf_xlatetof.3,v 1.1 2019/02/01 05:27:38 jsg Exp $
.\"
.Dd October 11, 2018
.Dt GELF_XLATETOF 3
.Os
.Sh NAME
.Nm elf32_xlate ,
.Nm elf64_xlate ,
.Nm gelf_xlate
.Nd translate data between files and memory
.Sh LIBRARY
.Lb libelf
.Sh SYNOPSIS
.In libelf.h
.Ft "Elf_Data *"
.Fn elf32_xlatetof "Elf_Data *dst" "Elf_Data *src" "unsigned int file_encoding"
.Ft "Elf_Data *"
.Fn elf32_xlatetom "Elf_Data *dst" "Elf_Data *src" "unsigned int file_encoding"
.Ft "Elf_Data *"
.Fn elf64_xlatetof "Elf_Data *dst" "Elf_Data *src" "unsigned int file_encoding"
.Ft "Elf_Data *"
.Fn elf64_xlatetom "Elf_Data *dst" "Elf_Data *src" "unsigned int file_encoding"
.In gelf.h
.Ft "Elf_Data *"
.Fo gelf_xlatetof
.Fa "Elf *elf"
.Fa "Elf_Data *dst"
.Fa "Elf_Data *src"
.Fa "unsigned int file_encoding"
.Fc
.Ft "Elf_Data *"
.Fo gelf_xlatetom
.Fa "Elf *elf"
.Fa "Elf_Data *dst"
.Fa "Elf_Data *src"
.Fa "unsigned int file_encoding"
.Fc
.Sh DESCRIPTION
These functions translate between the file and memory representations
of ELF data structures.
The in-memory representation of an ELF data structure would conform to
the byte ordering and data alignment restrictions dictated by the host
processor.
As described in
.Xr elf 3 ,
the file representation of this data structure could use a different byte
ordering from that of the host, or could use a different layout within
the file.
.Pp
Functions
.Fn elf32_xlatetom ,
.Fn elf64_xlatetom ,
and
.Fn gelf_xlatetom
translate data from file representations to native, in-memory representations.
Functions
.Fn elf32_xlatetof ,
.Fn elf64_xlatetof ,
and
.Fn gelf_xlatetof
translate data from in-memory representations to file representations.
.Pp
Argument
.Ar src
denotes an
.Vt Elf_Data
descriptor describing the source to be translated.
The following elements of the descriptor need to be set before
invoking these functions:
.Bl -hang -offset indent
.It Va d_buf
Set to a valid pointer value denoting the beginning of the data area
to be translated.
.It Va d_size
Set to the total size in bytes of the source data area to be
translated.
.It Va d_type
Set to the type of the source data being translated.
This value is one of the values defined in the
.Vt Elf_Type
enumeration.
The
.Vt Elf_Type
enumeration is described in
.Xr elf 3 .
.It Va d_version
Set to the version number of the ELF data structures being
translated.
Currently only version
.Dv EV_CURRENT
is supported.
.El
.Pp
Argument
.Ar dst
describes the destination buffer.
The following elements of the
.Vt Elf_Data
descriptor need to be set before invoking these functions:
.Bl -hang -offset indent
.It Va d_buf
Set to a valid pointer value that denotes the start of the destination
buffer that will hold translated data.
This value may be the same as that of the source buffer, in which case
an in-place conversion will be attempted.
.It Va d_size
Set to the size of the destination buffer in bytes.
This value will be modified if the function call succeeds.
.It Va d_version
Set to the desired version number of the destination.
Currently only version
.Dv EV_CURRENT
is supported.
.El
.Pp
These translations routines allow the source and destination buffers
to coincide, in which case an in-place translation will be done
if the destination is large enough to hold the translated data.
Other kinds of overlap between the source and destination buffers
are not permitted.
.Pp
On successful completion of the translation request the following
fields of the
.Ar dst
descriptor would be modified:
.Bl -hang -offset indent
.It Va d_size
Set to the size in bytes of the translated data.
.It Va d_type
Set to the
.Va d_type
value of the source data descriptor.
.El
.Pp
Argument
.Ar file_encoding
specifies the encoding in which the file objects are represented.
It must be one of:
.Bl -hang -offset indent
.It Dv ELFDATANONE
File objects use the library's native byte ordering.
.It Dv ELFDATA2LSB
File objects use a little-endian ordering.
.It Dv ELFDATA2MSB
File objects use a big-endian ordering.
.El
.Pp
The functions
.Fn gelf_xlatetof
and
.Fn gelf_xlatetom
select the appropriate translation scheme based on the properties of
argument
.Ar elf .
.Sh RETURN VALUES
These functions return argument
.Ar dst
if successful, or NULL in case of an error.
.Sh EXAMPLES
To translate a
.Vt GElf_Rel
structure to its LSB file representation use:
.Bd -literal -offset indent
Elf_Data dst, src;
GElf_Rel rel;
Elf *e;

e = ...; /* See elf_begin(3). */

/* Set up the 'src' descriptor. */
memset(&src, 0, sizeof src);
src.d_buf = &rel;
src.d_size = sizeof(rel);
src.d_type = ELF_T_REL;
src.d_version = EV_CURRENT;

/* Set up the 'dst' descriptor. */
memset(&dst, 0, sizeof dst);
dst.d_buf = filebuf;
dst.d_size = gelf_fsize(e, ELF_T_REL, 1, EV_CURRENT);
dst.d_version = EV_CURRENT;

if (gelf_xlatetof(e, &dst, &src, ELFDATA2LSB) == NULL) {
	printf("error: %s", elf_errmsg(0));
}
.Ed
.Sh ERRORS
These functions may fail with the following errors:
.Bl -tag -width "[ELF_E_RESOURCE]"
.It Bq Er ELF_E_ARGUMENT
One of arguments
.Ar src ,
.Ar dst
or
.Ar elf
was NULL.
.It Bq Er ELF_E_ARGUMENT
Arguments
.Ar src
and
.Ar dst
were equal.
.It Bq Er ELF_E_ARGUMENT
The desired encoding parameter was not one of
.Dv ELFDATANONE ,
.Dv ELFDATA2LSB
or
.Dv ELFDATA2MSB .
.It Bq Er ELF_E_ARGUMENT
The
.Ar d_type
field of argument
.Ar src
specified an unsupported type.
.It Bq Er ELF_E_DATA
The
.Ar src
argument specified a buffer size that was not an integral multiple of
its underlying type.
.It Bq Er ELF_E_DATA
The
.Ar dst
argument specified a buffer size that was too small.
.It Bq Er ELF_E_DATA
Argument
.Ar dst
specified a destination buffer that overlaps with the source
buffer.
.It Bq Er ELF_E_DATA
The destination buffer for a conversion to memory had an alignment
inappropriate for the underlying ELF type.
.It Bq Er ELF_E_DATA
The source buffer for a conversion to file had an alignment
inappropriate for the underlying ELF type.
.It Bq Er ELF_E_UNIMPL
The version numbers for arguments
.Ar dst
and
.Ar src
were not identical.
.It Bq Er ELF_E_UNIMPL
The argument
.Ar src
requested conversion for a type which is not currently
supported.
.It Bq Er ELF_E_VERSION
Argument
.Ar src
specified an unsupported version number.
.El
.Sh SEE ALSO
.Xr elf 3 ,
.Xr elf_getdata 3 ,
.Xr gelf 3