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<h4 class="subsection">9.15.5 HPPA Assembler Directives</h4>

<p><code>as</code> for the HPPA supports many additional directives for
compatibility with the native assembler.  This section describes them only
briefly.  For detailed information on HPPA-specific assembler directives, see
<cite>HP9000 Series 800 Assembly Language Reference Manual</cite> (HP 92432-90001).

   <p><a name="index-HPPA-directives-not-supported-1070"></a><code>as</code> does <em>not</em> support the following assembler directives
described in the HP manual:

<pre class="example">     .endm           .liston
     .enter          .locct
     .leave          .macro
     .listoff
</pre>
   <p><a name="index-g_t_0040code_007b_002eparam_007d-on-HPPA-1071"></a>Beyond those implemented for compatibility, <code>as</code> supports one
additional assembler directive for the HPPA: <code>.param</code>.  It conveys
register argument locations for static functions.  Its syntax closely follows
the <code>.export</code> directive.

   <p><a name="index-HPPA_002donly-directives-1072"></a>These are the additional directives in <code>as</code> for the HPPA:

     <dl>
<dt><code>.block </code><var>n</var><dt><code>.blockz </code><var>n</var><dd>Reserve <var>n</var> bytes of storage, and initialize them to zero.

     <br><dt><code>.call</code><dd>Mark the beginning of a procedure call.  Only the special case with <em>no
arguments</em> is allowed.

     <br><dt><code>.callinfo [ </code><var>param</var><code>=</code><var>value</var><code>, ... ]  [ </code><var>flag</var><code>, ... ]</code><dd>Specify a number of parameters and flags that define the environment for a
procedure.

     <p><var>param</var> may be any of &lsquo;<samp><span class="samp">frame</span></samp>&rsquo; (frame size), &lsquo;<samp><span class="samp">entry_gr</span></samp>&rsquo; (end of
general register range), &lsquo;<samp><span class="samp">entry_fr</span></samp>&rsquo; (end of float register range),
&lsquo;<samp><span class="samp">entry_sr</span></samp>&rsquo; (end of space register range).

     <p>The values for <var>flag</var> are &lsquo;<samp><span class="samp">calls</span></samp>&rsquo; or &lsquo;<samp><span class="samp">caller</span></samp>&rsquo; (proc has
subroutines), &lsquo;<samp><span class="samp">no_calls</span></samp>&rsquo; (proc does not call subroutines), &lsquo;<samp><span class="samp">save_rp</span></samp>&rsquo;
(preserve return pointer), &lsquo;<samp><span class="samp">save_sp</span></samp>&rsquo; (proc preserves stack pointer),
&lsquo;<samp><span class="samp">no_unwind</span></samp>&rsquo; (do not unwind this proc), &lsquo;<samp><span class="samp">hpux_int</span></samp>&rsquo; (proc is interrupt
routine).

     <br><dt><code>.code</code><dd>Assemble into the standard section called &lsquo;<samp><span class="samp">$TEXT$</span></samp>&rsquo;, subsection
&lsquo;<samp><span class="samp">$CODE$</span></samp>&rsquo;.

     <br><dt><code>.copyright "</code><var>string</var><code>"</code><dd>In the SOM object format, insert <var>string</var> into the object code, marked as a
copyright string.

     <br><dt><code>.copyright "</code><var>string</var><code>"</code><dd>In the ELF object format, insert <var>string</var> into the object code, marked as a
version string.

     <br><dt><code>.enter</code><dd>Not yet supported; the assembler rejects programs containing this directive.

     <br><dt><code>.entry</code><dd>Mark the beginning of a procedure.

     <br><dt><code>.exit</code><dd>Mark the end of a procedure.

     <br><dt><code>.export </code><var>name</var><code> [ ,</code><var>typ</var><code> ]  [ ,</code><var>param</var><code>=</code><var>r</var><code> ]</code><dd>Make a procedure <var>name</var> available to callers.  <var>typ</var>, if present, must
be one of &lsquo;<samp><span class="samp">absolute</span></samp>&rsquo;, &lsquo;<samp><span class="samp">code</span></samp>&rsquo; (ELF only, not SOM), &lsquo;<samp><span class="samp">data</span></samp>&rsquo;,
&lsquo;<samp><span class="samp">entry</span></samp>&rsquo;, &lsquo;<samp><span class="samp">data</span></samp>&rsquo;, &lsquo;<samp><span class="samp">entry</span></samp>&rsquo;, &lsquo;<samp><span class="samp">millicode</span></samp>&rsquo;, &lsquo;<samp><span class="samp">plabel</span></samp>&rsquo;,
&lsquo;<samp><span class="samp">pri_prog</span></samp>&rsquo;, or &lsquo;<samp><span class="samp">sec_prog</span></samp>&rsquo;.

     <p><var>param</var>, if present, provides either relocation information for the
procedure arguments and result, or a privilege level.  <var>param</var> may be
&lsquo;<samp><span class="samp">argw</span><var>n</var></samp>&rsquo; (where <var>n</var> ranges from <code>0</code> to <code>3</code>, and
indicates one of four one-word arguments); &lsquo;<samp><span class="samp">rtnval</span></samp>&rsquo; (the procedure's
result); or &lsquo;<samp><span class="samp">priv_lev</span></samp>&rsquo; (privilege level).  For arguments or the result,
<var>r</var> specifies how to relocate, and must be one of &lsquo;<samp><span class="samp">no</span></samp>&rsquo; (not
relocatable), &lsquo;<samp><span class="samp">gr</span></samp>&rsquo; (argument is in general register), &lsquo;<samp><span class="samp">fr</span></samp>&rsquo; (in
floating point register), or &lsquo;<samp><span class="samp">fu</span></samp>&rsquo; (upper half of float register). 
For &lsquo;<samp><span class="samp">priv_lev</span></samp>&rsquo;, <var>r</var> is an integer.

     <br><dt><code>.half </code><var>n</var><dd>Define a two-byte integer constant <var>n</var>; synonym for the portable
<code>as</code> directive <code>.short</code>.

     <br><dt><code>.import </code><var>name</var><code> [ ,</code><var>typ</var><code> ]</code><dd>Converse of <code>.export</code>; make a procedure available to call.  The arguments
use the same conventions as the first two arguments for <code>.export</code>.

     <br><dt><code>.label </code><var>name</var><dd>Define <var>name</var> as a label for the current assembly location.

     <br><dt><code>.leave</code><dd>Not yet supported; the assembler rejects programs containing this directive.

     <br><dt><code>.origin </code><var>lc</var><dd>Advance location counter to <var>lc</var>. Synonym for the <code>as</code>
portable directive <code>.org</code>.

     <br><dt><code>.param </code><var>name</var><code> [ ,</code><var>typ</var><code> ]  [ ,</code><var>param</var><code>=</code><var>r</var><code> ]</code><dd><!-- Not in HP manual; @sc{gnu} HPPA extension -->
Similar to <code>.export</code>, but used for static procedures.

     <br><dt><code>.proc</code><dd>Use preceding the first statement of a procedure.

     <br><dt><code>.procend</code><dd>Use following the last statement of a procedure.

     <br><dt><var>label</var><code> .reg </code><var>expr</var><dd><!-- ?? Not in HP manual (Jan 1988 vn) -->
Synonym for <code>.equ</code>; define <var>label</var> with the absolute expression
<var>expr</var> as its value.

     <br><dt><code>.space </code><var>secname</var><code> [ ,</code><var>params</var><code> ]</code><dd>Switch to section <var>secname</var>, creating a new section by that name if
necessary.  You may only use <var>params</var> when creating a new section, not
when switching to an existing one.  <var>secname</var> may identify a section by
number rather than by name.

     <p>If specified, the list <var>params</var> declares attributes of the section,
identified by keywords.  The keywords recognized are &lsquo;<samp><span class="samp">spnum=</span><var>exp</var></samp>&rsquo;
(identify this section by the number <var>exp</var>, an absolute expression),
&lsquo;<samp><span class="samp">sort=</span><var>exp</var></samp>&rsquo; (order sections according to this sort key when linking;
<var>exp</var> is an absolute expression), &lsquo;<samp><span class="samp">unloadable</span></samp>&rsquo; (section contains no
loadable data), &lsquo;<samp><span class="samp">notdefined</span></samp>&rsquo; (this section defined elsewhere), and
&lsquo;<samp><span class="samp">private</span></samp>&rsquo; (data in this section not available to other programs).

     <br><dt><code>.spnum </code><var>secnam</var><dd><!-- ?? Not in HP manual (Jan 1988) -->
Allocate four bytes of storage, and initialize them with the section number of
the section named <var>secnam</var>.  (You can define the section number with the
HPPA <code>.space</code> directive.)

     <p><a name="index-g_t_0040code_007bstring_007d-directive-on-HPPA-1073"></a><br><dt><code>.string "</code><var>str</var><code>"</code><dd>Copy the characters in the string <var>str</var> to the object file. 
See <a href="Strings.html#Strings">Strings</a>, for information on escape sequences you can use in
<code>as</code> strings.

     <p><em>Warning!</em> The HPPA version of <code>.string</code> differs from the
usual <code>as</code> definition: it does <em>not</em> write a zero byte
after copying <var>str</var>.

     <br><dt><code>.stringz "</code><var>str</var><code>"</code><dd>Like <code>.string</code>, but appends a zero byte after copying <var>str</var> to object
file.

     <br><dt><code>.subspa </code><var>name</var><code> [ ,</code><var>params</var><code> ]</code><dt><code>.nsubspa </code><var>name</var><code> [ ,</code><var>params</var><code> ]</code><dd>Similar to <code>.space</code>, but selects a subsection <var>name</var> within the
current section.  You may only specify <var>params</var> when you create a
subsection (in the first instance of <code>.subspa</code> for this <var>name</var>).

     <p>If specified, the list <var>params</var> declares attributes of the subsection,
identified by keywords.  The keywords recognized are &lsquo;<samp><span class="samp">quad=</span><var>expr</var></samp>&rsquo;
(&ldquo;quadrant&rdquo; for this subsection), &lsquo;<samp><span class="samp">align=</span><var>expr</var></samp>&rsquo; (alignment for
beginning of this subsection; a power of two), &lsquo;<samp><span class="samp">access=</span><var>expr</var></samp>&rsquo; (value
for &ldquo;access rights&rdquo; field), &lsquo;<samp><span class="samp">sort=</span><var>expr</var></samp>&rsquo; (sorting order for this
subspace in link), &lsquo;<samp><span class="samp">code_only</span></samp>&rsquo; (subsection contains only code),
&lsquo;<samp><span class="samp">unloadable</span></samp>&rsquo; (subsection cannot be loaded into memory), &lsquo;<samp><span class="samp">comdat</span></samp>&rsquo;
(subsection is comdat), &lsquo;<samp><span class="samp">common</span></samp>&rsquo; (subsection is common block),
&lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; (subsection may have duplicate names), or &lsquo;<samp><span class="samp">zero</span></samp>&rsquo;
(subsection is all zeros, do not write in object file).

     <p><code>.nsubspa</code> always creates a new subspace with the given name, even
if one with the same name already exists.

     <p>&lsquo;<samp><span class="samp">comdat</span></samp>&rsquo;, &lsquo;<samp><span class="samp">common</span></samp>&rsquo; and &lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; can be used to implement
various flavors of one-only support when using the SOM linker.  The SOM
linker only supports specific combinations of these flags.  The details
are not documented.  A brief description is provided here.

     <p>&lsquo;<samp><span class="samp">comdat</span></samp>&rsquo; provides a form of linkonce support.  It is useful for
both code and data subspaces.  A &lsquo;<samp><span class="samp">comdat</span></samp>&rsquo; subspace has a key symbol
marked by the &lsquo;<samp><span class="samp">is_comdat</span></samp>&rsquo; flag or &lsquo;<samp><span class="samp">ST_COMDAT</span></samp>&rsquo;.  Only the first
subspace for any given key is selected.  The key symbol becomes universal
in shared links.  This is similar to the behavior of &lsquo;<samp><span class="samp">secondary_def</span></samp>&rsquo;
symbols.

     <p>&lsquo;<samp><span class="samp">common</span></samp>&rsquo; provides Fortran named common support.  It is only useful
for data subspaces.  Symbols with the flag &lsquo;<samp><span class="samp">is_common</span></samp>&rsquo; retain this
flag in shared links.  Referencing a &lsquo;<samp><span class="samp">is_common</span></samp>&rsquo; symbol in a shared
library from outside the library doesn't work.  Thus, &lsquo;<samp><span class="samp">is_common</span></samp>&rsquo;
symbols must be output whenever they are needed.

     <p>&lsquo;<samp><span class="samp">common</span></samp>&rsquo; and &lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; together provide Cobol common support. 
The subspaces in this case must all be the same length.  Otherwise, this
support is similar to the Fortran common support.

     <p>&lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; by itself provides a type of one-only support for code. 
Only the first &lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; subspace is selected.  There is a rather
complex algorithm to compare subspaces.  Code symbols marked with the
&lsquo;<samp><span class="samp">dup_common</span></samp>&rsquo; flag are hidden.  This support was intended for "C++
duplicate inlines".

     <p>A simplified technique is used to mark the flags of symbols based on
the flags of their subspace.  A symbol with the scope SS_UNIVERSAL and
type ST_ENTRY, ST_CODE or ST_DATA is marked with the corresponding
settings of &lsquo;<samp><span class="samp">comdat</span></samp>&rsquo;, &lsquo;<samp><span class="samp">common</span></samp>&rsquo; and &lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo; from the
subspace, respectively.  This avoids having to introduce additional
directives to mark these symbols.  The HP assembler sets &lsquo;<samp><span class="samp">is_common</span></samp>&rsquo;
from &lsquo;<samp><span class="samp">common</span></samp>&rsquo;.  However, it doesn't set the &lsquo;<samp><span class="samp">dup_common</span></samp>&rsquo; from
&lsquo;<samp><span class="samp">dup_comm</span></samp>&rsquo;.  It doesn't have &lsquo;<samp><span class="samp">comdat</span></samp>&rsquo; support.

     <br><dt><code>.version "</code><var>str</var><code>"</code><dd>Write <var>str</var> as version identifier in object code. 
</dl>

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