GNU Info
(bfd.info)aout
a.out backends
==============
*Description*
BFD supports a number of different flavours of a.out format, though the
major differences are only the sizes of the structures on disk, and the
shape of the relocation information.
The support is split into a basic support file `aoutx.h' and other
files which derive functions from the base. One derivation file is
`aoutf1.h' (for a.out flavour 1), and adds to the basic a.out functions
support for sun3, sun4, 386 and 29k a.out files, to create a target
jump vector for a specific target.
This information is further split out into more specific files for
each machine, including `sunos.c' for sun3 and sun4, `newsos3.c' for
the Sony NEWS, and `demo64.c' for a demonstration of a 64 bit a.out
format.
The base file `aoutx.h' defines general mechanisms for reading and
writing records to and from disk and various other methods which BFD
requires. It is included by `aout32.c' and `aout64.c' to form the names
`aout_32_swap_exec_header_in', `aout_64_swap_exec_header_in', etc.
As an example, this is what goes on to make the back end for a sun4,
from `aout32.c':
#define ARCH_SIZE 32
#include "aoutx.h"
Which exports names:
...
aout_32_canonicalize_reloc
aout_32_find_nearest_line
aout_32_get_lineno
aout_32_get_reloc_upper_bound
...
from `sunos.c':
#define TARGET_NAME "a.out-sunos-big"
#define VECNAME sunos_big_vec
#include "aoutf1.h"
requires all the names from `aout32.c', and produces the jump vector
sunos_big_vec
The file `host-aout.c' is a special case. It is for a large set of
hosts that use "more or less standard" a.out files, and for which
cross-debugging is not interesting. It uses the standard 32-bit a.out
support routines, but determines the file offsets and addresses of the
text, data, and BSS sections, the machine architecture and machine
type, and the entry point address, in a host-dependent manner. Once
these values have been determined, generic code is used to handle the
object file.
When porting it to run on a new system, you must supply:
HOST_PAGE_SIZE
HOST_SEGMENT_SIZE
HOST_MACHINE_ARCH (optional)
HOST_MACHINE_MACHINE (optional)
HOST_TEXT_START_ADDR
HOST_STACK_END_ADDR
in the file `../include/sys/h-XXX.h' (for your host). These values,
plus the structures and macros defined in `a.out.h' on your host
system, will produce a BFD target that will access ordinary a.out files
on your host. To configure a new machine to use `host-aout.c', specify:
TDEFAULTS = -DDEFAULT_VECTOR=host_aout_big_vec
TDEPFILES= host-aout.o trad-core.o
in the `config/XXX.mt' file, and modify `configure.in' to use the
`XXX.mt' file (by setting "`bfd_target=XXX'") when your configuration
is selected.
Relocations
-----------
*Description*
The file `aoutx.h' provides for both the _standard_ and _extended_
forms of a.out relocation records.
The standard records contain only an address, a symbol index, and a
type field. The extended records (used on 29ks and sparcs) also have a
full integer for an addend.
Internal entry points
---------------------
*Description*
`aoutx.h' exports several routines for accessing the contents of an
a.out file, which are gathered and exported in turn by various format
specific files (eg sunos.c).
`aout_SIZE_swap_exec_header_in'
...............................
*Synopsis*
void aout_SIZE_swap_exec_header_in,
(bfd *abfd,
struct external_exec *raw_bytes,
struct internal_exec *execp);
*Description*
Swap the information in an executable header RAW_BYTES taken from a raw
byte stream memory image into the internal exec header structure EXECP.
`aout_SIZE_swap_exec_header_out'
................................
*Synopsis*
void aout_SIZE_swap_exec_header_out
(bfd *abfd,
struct internal_exec *execp,
struct external_exec *raw_bytes);
*Description*
Swap the information in an internal exec header structure EXECP into
the buffer RAW_BYTES ready for writing to disk.
`aout_SIZE_some_aout_object_p'
..............................
*Synopsis*
const bfd_target *aout_SIZE_some_aout_object_p
(bfd *abfd,
const bfd_target *(*callback_to_real_object_p) ());
*Description*
Some a.out variant thinks that the file open in ABFD checking is an
a.out file. Do some more checking, and set up for access if it really
is. Call back to the calling environment's "finish up" function just
before returning, to handle any last-minute setup.
`aout_SIZE_mkobject'
....................
*Synopsis*
boolean aout_SIZE_mkobject, (bfd *abfd);
*Description*
Initialize BFD ABFD for use with a.out files.
`aout_SIZE_machine_type'
........................
*Synopsis*
enum machine_type aout_SIZE_machine_type
(enum bfd_architecture arch,
unsigned long machine));
*Description*
Keep track of machine architecture and machine type for a.out's. Return
the `machine_type' for a particular architecture and machine, or
`M_UNKNOWN' if that exact architecture and machine can't be represented
in a.out format.
If the architecture is understood, machine type 0 (default) is
always understood.
`aout_SIZE_set_arch_mach'
.........................
*Synopsis*
boolean aout_SIZE_set_arch_mach,
(bfd *,
enum bfd_architecture arch,
unsigned long machine));
*Description*
Set the architecture and the machine of the BFD ABFD to the values ARCH
and MACHINE. Verify that ABFD's format can support the architecture
required.
`aout_SIZE_new_section_hook'
............................
*Synopsis*
boolean aout_SIZE_new_section_hook,
(bfd *abfd,
asection *newsect));
*Description*
Called by the BFD in response to a `bfd_make_section' request.
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