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<h3 class="section">3.2 a.out backends</h3>
<p><strong>Description</strong><br>
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.
<p>The support is split into a basic support file <span class="file">aoutx.h</span>
and other files which derive functions from the base. One
derivation file is <span class="file">aoutf1.h</span> (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.
<p>This information is further split out into more specific files
for each machine, including <span class="file">sunos.c</span> for sun3 and sun4,
<span class="file">newsos3.c</span> for the Sony NEWS, and <span class="file">demo64.c</span> for a
demonstration of a 64 bit a.out format.
<p>The base file <span class="file">aoutx.h</span> defines general mechanisms for
reading and writing records to and from disk and various
other methods which BFD requires. It is included by
<span class="file">aout32.c</span> and <span class="file">aout64.c</span> to form the names
<code>aout_32_swap_exec_header_in</code>, <code>aout_64_swap_exec_header_in</code>, etc.
<p>As an example, this is what goes on to make the back end for a
sun4, from <span class="file">aout32.c</span>:
<pre class="example"> #define ARCH_SIZE 32
#include "aoutx.h"
</pre>
<p>Which exports names:
<pre class="example"> ...
aout_32_canonicalize_reloc
aout_32_find_nearest_line
aout_32_get_lineno
aout_32_get_reloc_upper_bound
...
</pre>
<p>from <span class="file">sunos.c</span>:
<pre class="example"> #define TARGET_NAME "a.out-sunos-big"
#define VECNAME sunos_big_vec
#include "aoutf1.h"
</pre>
<p>requires all the names from <span class="file">aout32.c</span>, and produces the jump vector
<pre class="example"> sunos_big_vec
</pre>
<p>The file <span class="file">host-aout.c</span> 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.
<p>When porting it to run on a new system, you must supply:
<pre class="example"> HOST_PAGE_SIZE
HOST_SEGMENT_SIZE
HOST_MACHINE_ARCH (optional)
HOST_MACHINE_MACHINE (optional)
HOST_TEXT_START_ADDR
HOST_STACK_END_ADDR
</pre>
<p>in the file <span class="file">../include/sys/h-</span><var>XXX</var><span class="file">.h</span> (for your host). These
values, plus the structures and macros defined in <span class="file">a.out.h</span> 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 <span class="file">host-aout.c</span>, specify:
<pre class="example"> TDEFAULTS = -DDEFAULT_VECTOR=host_aout_big_vec
TDEPFILES= host-aout.o trad-core.o
</pre>
<p>in the <span class="file">config/</span><var>XXX</var><span class="file">.mt</span> file, and modify <span class="file">configure.in</span>
to use the
<var>XXX</var><span class="file">.mt</span> file (by setting "<code>bfd_target=XXX</code>") when your
configuration is selected.
<h4 class="subsection">3.2.1 Relocations</h4>
<p><strong>Description</strong><br>
The file <span class="file">aoutx.h</span> provides for both the <em>standard</em>
and <em>extended</em> forms of a.out relocation records.
<p>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.
<h4 class="subsection">3.2.2 Internal entry points</h4>
<p><strong>Description</strong><br>
<span class="file">aoutx.h</span> 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).
<p><a name="index-aout_005f_0040var_007bsize_007d_005fswap_005fexec_005fheader_005fin-1390"></a>
<h5 class="subsubsection">3.2.2.1 <code>aout_</code><var>size</var><code>_swap_exec_header_in</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> void aout_<var>size</var>_swap_exec_header_in,
(bfd *abfd,
struct external_exec *bytes,
struct internal_exec *execp);
</pre>
<p><strong>Description</strong><br>
Swap the information in an executable header <var>raw_bytes</var> taken
from a raw byte stream memory image into the internal exec header
structure <var>execp</var>.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fswap_005fexec_005fheader_005fout-1391"></a>
<h5 class="subsubsection">3.2.2.2 <code>aout_</code><var>size</var><code>_swap_exec_header_out</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> void aout_<var>size</var>_swap_exec_header_out
(bfd *abfd,
struct internal_exec *execp,
struct external_exec *raw_bytes);
</pre>
<p><strong>Description</strong><br>
Swap the information in an internal exec header structure
<var>execp</var> into the buffer <var>raw_bytes</var> ready for writing to disk.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fsome_005faout_005fobject_005fp-1392"></a>
<h5 class="subsubsection">3.2.2.3 <code>aout_</code><var>size</var><code>_some_aout_object_p</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> const bfd_target *aout_<var>size</var>_some_aout_object_p
(bfd *abfd,
struct internal_exec *execp,
const bfd_target *(*callback_to_real_object_p) (bfd *));
</pre>
<p><strong>Description</strong><br>
Some a.out variant thinks that the file open in <var>abfd</var>
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.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fmkobject-1393"></a>
<h5 class="subsubsection">3.2.2.4 <code>aout_</code><var>size</var><code>_mkobject</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> bfd_boolean aout_<var>size</var>_mkobject, (bfd *abfd);
</pre>
<p><strong>Description</strong><br>
Initialize BFD <var>abfd</var> for use with a.out files.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fmachine_005ftype-1394"></a>
<h5 class="subsubsection">3.2.2.5 <code>aout_</code><var>size</var><code>_machine_type</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> enum machine_type aout_<var>size</var>_machine_type
(enum bfd_architecture arch,
unsigned long machine,
bfd_boolean *unknown);
</pre>
<p><strong>Description</strong><br>
Keep track of machine architecture and machine type for
a.out's. Return the <code>machine_type</code> for a particular
architecture and machine, or <code>M_UNKNOWN</code> if that exact architecture
and machine can't be represented in a.out format.
<p>If the architecture is understood, machine type 0 (default)
is always understood.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fset_005farch_005fmach-1395"></a>
<h5 class="subsubsection">3.2.2.6 <code>aout_</code><var>size</var><code>_set_arch_mach</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> bfd_boolean aout_<var>size</var>_set_arch_mach,
(bfd *,
enum bfd_architecture arch,
unsigned long machine);
</pre>
<p><strong>Description</strong><br>
Set the architecture and the machine of the BFD <var>abfd</var> to the
values <var>arch</var> and <var>machine</var>. Verify that <var>abfd</var>'s format
can support the architecture required.
<p><a name="index-aout_005f_0040var_007bsize_007d_005fnew_005fsection_005fhook-1396"></a>
<h5 class="subsubsection">3.2.2.7 <code>aout_</code><var>size</var><code>_new_section_hook</code></h5>
<p><strong>Synopsis</strong>
<pre class="example"> bfd_boolean aout_<var>size</var>_new_section_hook,
(bfd *abfd,
asection *newsect);
</pre>
<p><strong>Description</strong><br>
Called by the BFD in response to a <code>bfd_make_section</code>
request.
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