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<title>Using as: Alpha Directives</title>
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<a name="Alpha-Directives"></a>
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<div class="header">
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<p>
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Next: <a href="Alpha-Opcodes.html#Alpha-Opcodes" accesskey="n" rel="next">Alpha Opcodes</a>, Previous: <a href="Alpha-Floating-Point.html#Alpha-Floating-Point" accesskey="p" rel="prev">Alpha Floating Point</a>, Up: <a href="Alpha_002dDependent.html#Alpha_002dDependent" accesskey="u" rel="up">Alpha-Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Alpha-Assembler-Directives"></a>
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<h4 class="subsection">9.2.5 Alpha Assembler Directives</h4>
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<p><code>as</code> for the Alpha supports many additional directives for
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compatibility with the native assembler. This section describes them only
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briefly.
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</p>
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<a name="index-Alpha_002donly-directives"></a>
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<p>These are the additional directives in <code>as</code> for the Alpha:
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</p>
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<dl compact="compact">
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<dt><code>.arch <var>cpu</var></code></dt>
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<dd><p>Specifies the target processor. This is equivalent to the
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<samp>-m<var>cpu</var></samp> command-line option. See <a href="Alpha-Options.html#Alpha-Options">Options</a>,
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for a list of values for <var>cpu</var>.
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</p>
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</dd>
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<dt><code>.ent <var>function</var>[, <var>n</var>]</code></dt>
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<dd><p>Mark the beginning of <var>function</var>. An optional number may follow for
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compatibility with the OSF/1 assembler, but is ignored. When generating
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<code>.mdebug</code> information, this will create a procedure descriptor for
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the function. In ELF, it will mark the symbol as a function a-la the
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generic <code>.type</code> directive.
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</p>
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</dd>
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<dt><code>.end <var>function</var></code></dt>
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<dd><p>Mark the end of <var>function</var>. In ELF, it will set the size of the symbol
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a-la the generic <code>.size</code> directive.
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</p>
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</dd>
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<dt><code>.mask <var>mask</var>, <var>offset</var></code></dt>
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<dd><p>Indicate which of the integer registers are saved in the current
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function’s stack frame. <var>mask</var> is interpreted a bit mask in which
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bit <var>n</var> set indicates that register <var>n</var> is saved. The registers
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are saved in a block located <var>offset</var> bytes from the <em>canonical
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frame address</em> (CFA) which is the value of the stack pointer on entry to
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the function. The registers are saved sequentially, except that the
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return address register (normally <code>$26</code>) is saved first.
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</p>
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<p>This and the other directives that describe the stack frame are
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currently only used when generating <code>.mdebug</code> information. They
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may in the future be used to generate DWARF2 <code>.debug_frame</code> unwind
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information for hand written assembly.
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</p>
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</dd>
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<dt><code>.fmask <var>mask</var>, <var>offset</var></code></dt>
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<dd><p>Indicate which of the floating-point registers are saved in the current
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stack frame. The <var>mask</var> and <var>offset</var> parameters are interpreted
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as with <code>.mask</code>.
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</p>
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</dd>
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<dt><code>.frame <var>framereg</var>, <var>frameoffset</var>, <var>retreg</var>[, <var>argoffset</var>]</code></dt>
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<dd><p>Describes the shape of the stack frame. The frame pointer in use is
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<var>framereg</var>; normally this is either <code>$fp</code> or <code>$sp</code>. The
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frame pointer is <var>frameoffset</var> bytes below the CFA. The return
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address is initially located in <var>retreg</var> until it is saved as
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indicated in <code>.mask</code>. For compatibility with OSF/1 an optional
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<var>argoffset</var> parameter is accepted and ignored. It is believed to
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indicate the offset from the CFA to the saved argument registers.
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</p>
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</dd>
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<dt><code>.prologue <var>n</var></code></dt>
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<dd><p>Indicate that the stack frame is set up and all registers have been
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spilled. The argument <var>n</var> indicates whether and how the function
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uses the incoming <em>procedure vector</em> (the address of the called
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function) in <code>$27</code>. 0 indicates that <code>$27</code> is not used; 1
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indicates that the first two instructions of the function use <code>$27</code>
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to perform a load of the GP register; 2 indicates that <code>$27</code> is
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used in some non-standard way and so the linker cannot elide the load of
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the procedure vector during relaxation.
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</p>
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</dd>
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<dt><code>.usepv <var>function</var>, <var>which</var></code></dt>
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<dd><p>Used to indicate the use of the <code>$27</code> register, similar to
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<code>.prologue</code>, but without the other semantics of needing to
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be inside an open <code>.ent</code>/<code>.end</code> block.
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</p>
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<p>The <var>which</var> argument should be either <code>no</code>, indicating that
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<code>$27</code> is not used, or <code>std</code>, indicating that the first two
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instructions of the function perform a GP load.
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</p>
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<p>One might use this directive instead of <code>.prologue</code> if you are
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also using dwarf2 CFI directives.
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</p>
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</dd>
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<dt><code>.gprel32 <var>expression</var></code></dt>
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<dd><p>Computes the difference between the address in <var>expression</var> and the
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GP for the current object file, and stores it in 4 bytes. In addition
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to being smaller than a full 8 byte address, this also does not require
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a dynamic relocation when used in a shared library.
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</p>
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</dd>
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<dt><code>.t_floating <var>expression</var></code></dt>
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<dd><p>Stores <var>expression</var> as an <small>IEEE</small> double precision value.
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</p>
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</dd>
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<dt><code>.s_floating <var>expression</var></code></dt>
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<dd><p>Stores <var>expression</var> as an <small>IEEE</small> single precision value.
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</p>
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</dd>
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<dt><code>.f_floating <var>expression</var></code></dt>
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<dd><p>Stores <var>expression</var> as a VAX F format value.
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</p>
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</dd>
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<dt><code>.g_floating <var>expression</var></code></dt>
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<dd><p>Stores <var>expression</var> as a VAX G format value.
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</p>
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</dd>
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<dt><code>.d_floating <var>expression</var></code></dt>
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<dd><p>Stores <var>expression</var> as a VAX D format value.
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</p>
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</dd>
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<dt><code>.set <var>feature</var></code></dt>
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<dd><p>Enables or disables various assembler features. Using the positive
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name of the feature enables while using ‘<samp>no<var>feature</var></samp>’ disables.
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</p>
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<dl compact="compact">
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<dt><code>at</code></dt>
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<dd><p>Indicates that macro expansions may clobber the <em>assembler
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temporary</em> (<code>$at</code> or <code>$28</code>) register. Some macros may not be
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expanded without this and will generate an error message if <code>noat</code>
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is in effect. When <code>at</code> is in effect, a warning will be generated
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if <code>$at</code> is used by the programmer.
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</p>
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</dd>
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<dt><code>macro</code></dt>
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<dd><p>Enables the expansion of macro instructions. Note that variants of real
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instructions, such as <code>br label</code> vs <code>br $31,label</code> are
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considered alternate forms and not macros.
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</p>
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</dd>
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<dt><code>move</code></dt>
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<dt><code>reorder</code></dt>
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<dt><code>volatile</code></dt>
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<dd><p>These control whether and how the assembler may re-order instructions.
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Accepted for compatibility with the OSF/1 assembler, but <code>as</code>
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does not do instruction scheduling, so these features are ignored.
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</p></dd>
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</dl>
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</dd>
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</dl>
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<p>The following directives are recognized for compatibility with the OSF/1
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assembler but are ignored.
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</p>
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<div class="example">
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<pre class="example">.proc .aproc
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.reguse .livereg
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.option .aent
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.ugen .eflag
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.alias .noalias
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Alpha-Opcodes.html#Alpha-Opcodes" accesskey="n" rel="next">Alpha Opcodes</a>, Previous: <a href="Alpha-Floating-Point.html#Alpha-Floating-Point" accesskey="p" rel="prev">Alpha Floating Point</a>, Up: <a href="Alpha_002dDependent.html#Alpha_002dDependent" accesskey="u" rel="up">Alpha-Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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