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