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@section a.out backends

@strong{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 @file{aoutx.h}

and other files which derive functions from the base. One

derivation file is @file{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 @file{sunos.c} for sun3 and sun4,

@file{newsos3.c} for the Sony NEWS, and @file{demo64.c} for a

demonstration of a 64 bit a.out format.

The base file @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

@file{aout32.c} and @file{aout64.c} to form the names

@code{aout_32_swap_exec_header_in}, @code{aout_64_swap_exec_header_in}, etc.

As an example, this is what goes on to make the back end for a

sun4, from @file{aout32.c}:

@example

       #define ARCH_SIZE 32

       #include "aoutx.h"

@end example

Which exports names:

@example

       ...

       aout_32_canonicalize_reloc

       aout_32_find_nearest_line

       aout_32_get_lineno

       aout_32_get_reloc_upper_bound

       ...

@end example

from @file{sunos.c}:

@example

       #define TARGET_NAME "a.out-sunos-big"

       #define VECNAME    sunos_big_vec

       #include "aoutf1.h"

@end example

requires all the names from @file{aout32.c}, and produces the jump vector

@example

       sunos_big_vec

@end example

The file @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:

@example

        HOST_PAGE_SIZE

        HOST_SEGMENT_SIZE

        HOST_MACHINE_ARCH       (optional)

        HOST_MACHINE_MACHINE    (optional)

        HOST_TEXT_START_ADDR

        HOST_STACK_END_ADDR

@end example

in the file @file{../include/sys/h-@var{XXX}.h} (for your host).  These

values, plus the structures and macros defined in @file{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 @file{host-aout.c}, specify:

@example

       TDEFAULTS = -DDEFAULT_VECTOR=host_aout_big_vec

       TDEPFILES= host-aout.o trad-core.o

@end example

in the @file{config/@var{XXX}.mt} file, and modify @file{configure.in}

to use the

@file{@var{XXX}.mt} file (by setting "@code{bfd_target=XXX}") when your

configuration is selected.

@subsection Relocations

@strong{Description}@*

The file @file{aoutx.h} provides for both the @emph{standard}

and @emph{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.

@subsection Internal entry points

@strong{Description}@*

@file{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).

@findex aout_@var{size}_swap_exec_header_in

@subsubsection @code{aout_@var{size}_swap_exec_header_in}

@strong{Synopsis}

@example

void aout_@var{size}_swap_exec_header_in,

   (bfd *abfd,

    struct external_exec *bytes,

    struct internal_exec *execp);

@end example

@strong{Description}@*

Swap the information in an executable header @var{raw_bytes} taken

from a raw byte stream memory image into the internal exec header

structure @var{execp}.

@findex aout_@var{size}_swap_exec_header_out

@subsubsection @code{aout_@var{size}_swap_exec_header_out}

@strong{Synopsis}

@example

void aout_@var{size}_swap_exec_header_out

   (bfd *abfd,

    struct internal_exec *execp,

    struct external_exec *raw_bytes);

@end example

@strong{Description}@*

Swap the information in an internal exec header structure

@var{execp} into the buffer @var{raw_bytes} ready for writing to disk.

@findex aout_@var{size}_some_aout_object_p

@subsubsection @code{aout_@var{size}_some_aout_object_p}

@strong{Synopsis}

@example

const bfd_target *aout_@var{size}_some_aout_object_p

   (bfd *abfd,

    struct internal_exec *execp,

    const bfd_target *(*callback_to_real_object_p) (bfd *));

@end example

@strong{Description}@*

Some a.out variant thinks that the file open in @var{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.

@findex aout_@var{size}_mkobject

@subsubsection @code{aout_@var{size}_mkobject}

@strong{Synopsis}

@example

bfd_boolean aout_@var{size}_mkobject, (bfd *abfd);

@end example

@strong{Description}@*

Initialize BFD @var{abfd} for use with a.out files.

@findex aout_@var{size}_machine_type

@subsubsection @code{aout_@var{size}_machine_type}

@strong{Synopsis}

@example

enum machine_type  aout_@var{size}_machine_type

   (enum bfd_architecture arch,

    unsigned long machine,

    bfd_boolean *unknown);

@end example

@strong{Description}@*

Keep track of machine architecture and machine type for

a.out's. Return the @code{machine_type} for a particular

architecture and machine, or @code{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.

@findex aout_@var{size}_set_arch_mach

@subsubsection @code{aout_@var{size}_set_arch_mach}

@strong{Synopsis}

@example

bfd_boolean aout_@var{size}_set_arch_mach,

   (bfd *,

    enum bfd_architecture arch,

    unsigned long machine);

@end example

@strong{Description}@*

Set the architecture and the machine of the BFD @var{abfd} to the

values @var{arch} and @var{machine}.  Verify that @var{abfd}'s format

can support the architecture required.

@findex aout_@var{size}_new_section_hook

@subsubsection @code{aout_@var{size}_new_section_hook}

@strong{Synopsis}

@example

bfd_boolean aout_@var{size}_new_section_hook,

   (bfd *abfd,

    asection *newsect);

@end example

@strong{Description}@*

Called by the BFD in response to a @code{bfd_make_section}

request.