<html lang="en">
<head>
<title>MMIX-Opts - Using as</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Using as">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="MMIX_002dDependent.html#MMIX_002dDependent" title="MMIX-Dependent">
<link rel="next" href="MMIX_002dExpand.html#MMIX_002dExpand" title="MMIX-Expand">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
This file documents the GNU Assembler "as".

Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2000, 2001, 2002, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts.  A copy of the license is included in the
section entitled ``GNU Free Documentation License''.

-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
  pre.display { font-family:inherit }
  pre.format  { font-family:inherit }
  pre.smalldisplay { font-family:inherit; font-size:smaller }
  pre.smallformat  { font-family:inherit; font-size:smaller }
  pre.smallexample { font-size:smaller }
  pre.smalllisp    { font-size:smaller }
  span.sc    { font-variant:small-caps }
  span.roman { font-family:serif; font-weight:normal; } 
  span.sansserif { font-family:sans-serif; font-weight:normal; } 
--></style>
<link rel="stylesheet" type="text/css" href="../cs.css">
</head>
<body>
<div class="node">
<a name="MMIX-Opts"></a>
<a name="MMIX_002dOpts"></a>
<p>
Next:&nbsp;<a rel="next" accesskey="n" href="MMIX_002dExpand.html#MMIX_002dExpand">MMIX-Expand</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="MMIX_002dDependent.html#MMIX_002dDependent">MMIX-Dependent</a>
<hr>
</div>

<h4 class="subsection">9.25.1 Command-line Options</h4>

<p><a name="index-options_002c-MMIX-1312"></a><a name="index-MMIX-options-1313"></a>The MMIX version of <code>as</code> has some machine-dependent options.

   <p><a name="index-g_t_0040samp_007b_002d_002dfixed_002dspecial_002dregister_002dnames_007d-command-line-option_002c-MMIX-1314"></a>When &lsquo;<samp><span class="samp">--fixed-special-register-names</span></samp>&rsquo; is specified, only the register
names specified in <a href="MMIX_002dRegs.html#MMIX_002dRegs">MMIX-Regs</a> are recognized in the instructions
<code>PUT</code> and <code>GET</code>.

   <p><a name="index-g_t_0040samp_007b_002d_002dglobalize_002dsymbols_007d-command-line-option_002c-MMIX-1315"></a>You can use the &lsquo;<samp><span class="samp">--globalize-symbols</span></samp>&rsquo; to make all symbols global. 
This option is useful when splitting up a <code>mmixal</code> program into
several files.

   <p><a name="index-g_t_0040samp_007b_002d_002dgnu_002dsyntax_007d-command-line-option_002c-MMIX-1316"></a>The &lsquo;<samp><span class="samp">--gnu-syntax</span></samp>&rsquo; turns off most syntax compatibility with
<code>mmixal</code>.  Its usability is currently doubtful.

   <p><a name="index-g_t_0040samp_007b_002d_002drelax_007d-command-line-option_002c-MMIX-1317"></a>The &lsquo;<samp><span class="samp">--relax</span></samp>&rsquo; option is not fully supported, but will eventually make
the object file prepared for linker relaxation.

   <p><a name="index-g_t_0040samp_007b_002d_002dno_002dpredefined_002dsyms_007d-command-line-option_002c-MMIX-1318"></a>If you want to avoid inadvertently calling a predefined symbol and would
rather get an error, for example when using <code>as</code> with a
compiler or other machine-generated code, specify
&lsquo;<samp><span class="samp">--no-predefined-syms</span></samp>&rsquo;.  This turns off built-in predefined
definitions of all such symbols, including rounding-mode symbols, segment
symbols, &lsquo;<samp><span class="samp">BIT</span></samp>&rsquo; symbols, and <code>TRAP</code> symbols used in <code>mmix</code>
&ldquo;system calls&rdquo;.  It also turns off predefined special-register names,
except when used in <code>PUT</code> and <code>GET</code> instructions.

   <p><a name="index-g_t_0040samp_007b_002d_002dno_002dexpand_007d-command-line-option_002c-MMIX-1319"></a>By default, some instructions are expanded to fit the size of the operand
or an external symbol (see <a href="MMIX_002dExpand.html#MMIX_002dExpand">MMIX-Expand</a>).  By passing
&lsquo;<samp><span class="samp">--no-expand</span></samp>&rsquo;, no such expansion will be done, instead causing errors
at link time if the operand does not fit.

   <p><a name="index-g_t_0040samp_007b_002d_002dno_002dmerge_002dgregs_007d-command-line-option_002c-MMIX-1320"></a>The <code>mmixal</code> documentation (see <a href="mmixsite.html#mmixsite">mmixsite</a>) specifies that global
registers allocated with the &lsquo;<samp><span class="samp">GREG</span></samp>&rsquo; directive (see <a href="MMIX_002dgreg.html#MMIX_002dgreg">MMIX-greg</a>) and
initialized to the same non-zero value, will refer to the same global
register.  This isn't strictly enforceable in <code>as</code> since the
final addresses aren't known until link-time, but it will do an effort
unless the &lsquo;<samp><span class="samp">--no-merge-gregs</span></samp>&rsquo; option is specified.  (Register merging
isn't yet implemented in <code>ld</code>.)

   <p><a name="index-g_t_0040samp_007b_002dx_007d-command-line-option_002c-MMIX-1321"></a><code>as</code> will warn every time it expands an instruction to fit an
operand unless the option &lsquo;<samp><span class="samp">-x</span></samp>&rsquo; is specified.  It is believed that
this behaviour is more useful than just mimicking <code>mmixal</code>'s
behaviour, in which instructions are only expanded if the &lsquo;<samp><span class="samp">-x</span></samp>&rsquo; option
is specified, and assembly fails otherwise, when an instruction needs to
be expanded.  It needs to be kept in mind that <code>mmixal</code> is both an
assembler and linker, while <code>as</code> will expand instructions
that at link stage can be contracted.  (Though linker relaxation isn't yet
implemented in <code>ld</code>.)  The option &lsquo;<samp><span class="samp">-x</span></samp>&rsquo; also imples
&lsquo;<samp><span class="samp">--linker-allocated-gregs</span></samp>&rsquo;.

   <p><a name="index-g_t_0040samp_007b_002d_002dno_002dpushj_002dstubs_007d-command-line-option_002c-MMIX-1322"></a><a name="index-g_t_0040samp_007b_002d_002dno_002dstubs_007d-command-line-option_002c-MMIX-1323"></a>If instruction expansion is enabled, <code>as</code> can expand a
&lsquo;<samp><span class="samp">PUSHJ</span></samp>&rsquo; instruction into a series of instructions.  The shortest
expansion is to not expand it, but just mark the call as redirectable to a
stub, which <code>ld</code> creates at link-time, but only if the
original &lsquo;<samp><span class="samp">PUSHJ</span></samp>&rsquo; instruction is found not to reach the target.  The
stub consists of the necessary instructions to form a jump to the target. 
This happens if <code>as</code> can assert that the &lsquo;<samp><span class="samp">PUSHJ</span></samp>&rsquo;
instruction can reach such a stub.  The option &lsquo;<samp><span class="samp">--no-pushj-stubs</span></samp>&rsquo;
disables this shorter expansion, and the longer series of instructions is
then created at assembly-time.  The option &lsquo;<samp><span class="samp">--no-stubs</span></samp>&rsquo; is a synonym,
intended for compatibility with future releases, where generation of stubs
for other instructions may be implemented.

   <p><a name="index-g_t_0040samp_007b_002d_002dlinker_002dallocated_002dgregs_007d-command-line-option_002c-MMIX-1324"></a>Usually a two-operand-expression (see <a href="GREG_002dbase.html#GREG_002dbase">GREG-base</a>) without a matching
&lsquo;<samp><span class="samp">GREG</span></samp>&rsquo; directive is treated as an error by <code>as</code>.  When
the option &lsquo;<samp><span class="samp">--linker-allocated-gregs</span></samp>&rsquo; is in effect, they are instead
passed through to the linker, which will allocate as many global registers
as is needed.

   </body></html>