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| <a name="g_t_002emacro"></a> |
| <h3 class="section">7.79 <code>.macro</code></h3> |
| |
| <a name="index-macros"></a> |
| <p>The commands <code>.macro</code> and <code>.endm</code> allow you to define macros that |
| generate assembly output. For example, this definition specifies a macro |
| <code>sum</code> that puts a sequence of numbers into memory: |
| </p> |
| <div class="example"> |
| <pre class="example"> .macro sum from=0, to=5 |
| .long \from |
| .if \to-\from |
| sum "(\from+1)",\to |
| .endif |
| .endm |
| </pre></div> |
| |
| <p>With that definition, ‘<samp>SUM 0,5</samp>’ is equivalent to this assembly input: |
| </p> |
| <div class="example"> |
| <pre class="example"> .long 0 |
| .long 1 |
| .long 2 |
| .long 3 |
| .long 4 |
| .long 5 |
| </pre></div> |
| |
| <dl compact="compact"> |
| <dt><code>.macro <var>macname</var></code> |
| <a name="index-_002emacro-macname"></a> |
| </dt> |
| <dt><code>.macro <var>macname</var> <var>macargs</var> …</code> |
| <a name="index-_002emacro-macname-macargs-_2026"></a> |
| </dt> |
| <dd><a name="index-macro-directive"></a> |
| <p>Begin the definition of a macro called <var>macname</var>. If your macro |
| definition requires arguments, specify their names after the macro name, |
| separated by commas or spaces. You can qualify the macro argument to |
| indicate whether all invocations must specify a non-blank value (through |
| ‘<samp>:<code>req</code></samp>’), or whether it takes all of the remaining arguments |
| (through ‘<samp>:<code>vararg</code></samp>’). You can supply a default value for any |
| macro argument by following the name with ‘<samp>=<var>deflt</var></samp>’. You |
| cannot define two macros with the same <var>macname</var> unless it has been |
| subject to the <code>.purgem</code> directive (see <a href="Purgem.html#Purgem">Purgem</a>) between the two |
| definitions. For example, these are all valid <code>.macro</code> statements: |
| </p> |
| <dl compact="compact"> |
| <dt><code>.macro comm</code></dt> |
| <dd><p>Begin the definition of a macro called <code>comm</code>, which takes no |
| arguments. |
| </p> |
| </dd> |
| <dt><code>.macro plus1 p, p1</code></dt> |
| <dt><code>.macro plus1 p p1</code></dt> |
| <dd><p>Either statement begins the definition of a macro called <code>plus1</code>, |
| which takes two arguments; within the macro definition, write |
| ‘<samp>\p</samp>’ or ‘<samp>\p1</samp>’ to evaluate the arguments. |
| </p> |
| </dd> |
| <dt><code>.macro reserve_str p1=0 p2</code></dt> |
| <dd><p>Begin the definition of a macro called <code>reserve_str</code>, with two |
| arguments. The first argument has a default value, but not the second. |
| After the definition is complete, you can call the macro either as |
| ‘<samp>reserve_str <var>a</var>,<var>b</var></samp>’ (with ‘<samp>\p1</samp>’ evaluating to |
| <var>a</var> and ‘<samp>\p2</samp>’ evaluating to <var>b</var>), or as ‘<samp>reserve_str |
| ,<var>b</var></samp>’ (with ‘<samp>\p1</samp>’ evaluating as the default, in this case |
| ‘<samp>0</samp>’, and ‘<samp>\p2</samp>’ evaluating to <var>b</var>). |
| </p> |
| </dd> |
| <dt><code>.macro m p1:req, p2=0, p3:vararg</code></dt> |
| <dd><p>Begin the definition of a macro called <code>m</code>, with at least three |
| arguments. The first argument must always have a value specified, but |
| not the second, which instead has a default value. The third formal |
| will get assigned all remaining arguments specified at invocation time. |
| </p> |
| <p>When you call a macro, you can specify the argument values either by |
| position, or by keyword. For example, ‘<samp>sum 9,17</samp>’ is equivalent to |
| ‘<samp>sum to=17, from=9</samp>’. |
| </p> |
| </dd> |
| </dl> |
| |
| <p>Note that since each of the <var>macargs</var> can be an identifier exactly |
| as any other one permitted by the target architecture, there may be |
| occasional problems if the target hand-crafts special meanings to certain |
| characters when they occur in a special position. For example, if the colon |
| (<code>:</code>) is generally permitted to be part of a symbol name, but the |
| architecture specific code special-cases it when occurring as the final |
| character of a symbol (to denote a label), then the macro parameter |
| replacement code will have no way of knowing that and consider the whole |
| construct (including the colon) an identifier, and check only this |
| identifier for being the subject to parameter substitution. So for example |
| this macro definition: |
| </p> |
| <div class="example"> |
| <pre class="example"> .macro label l |
| \l: |
| .endm |
| </pre></div> |
| |
| <p>might not work as expected. Invoking ‘<samp>label foo</samp>’ might not create a label |
| called ‘<samp>foo</samp>’ but instead just insert the text ‘<samp>\l:</samp>’ into the |
| assembler source, probably generating an error about an unrecognised |
| identifier. |
| </p> |
| <p>Similarly problems might occur with the period character (‘<samp>.</samp>’) |
| which is often allowed inside opcode names (and hence identifier names). So |
| for example constructing a macro to build an opcode from a base name and a |
| length specifier like this: |
| </p> |
| <div class="example"> |
| <pre class="example"> .macro opcode base length |
| \base.\length |
| .endm |
| </pre></div> |
| |
| <p>and invoking it as ‘<samp>opcode store l</samp>’ will not create a ‘<samp>store.l</samp>’ |
| instruction but instead generate some kind of error as the assembler tries to |
| interpret the text ‘<samp>\base.\length</samp>’. |
| </p> |
| <p>There are several possible ways around this problem: |
| </p> |
| <dl compact="compact"> |
| <dt><code>Insert white space</code></dt> |
| <dd><p>If it is possible to use white space characters then this is the simplest |
| solution. eg: |
| </p> |
| <div class="example"> |
| <pre class="example"> .macro label l |
| \l : |
| .endm |
| </pre></div> |
| |
| </dd> |
| <dt><code>Use ‘<samp>\()</samp>’</code></dt> |
| <dd><p>The string ‘<samp>\()</samp>’ can be used to separate the end of a macro argument from |
| the following text. eg: |
| </p> |
| <div class="example"> |
| <pre class="example"> .macro opcode base length |
| \base\().\length |
| .endm |
| </pre></div> |
| |
| </dd> |
| <dt><code>Use the alternate macro syntax mode</code></dt> |
| <dd><p>In the alternative macro syntax mode the ampersand character (‘<samp>&</samp>’) can be |
| used as a separator. eg: |
| </p> |
| <div class="example"> |
| <pre class="example"> .altmacro |
| .macro label l |
| l&: |
| .endm |
| </pre></div> |
| </dd> |
| </dl> |
| |
| <p>Note: this problem of correctly identifying string parameters to pseudo ops |
| also applies to the identifiers used in <code>.irp</code> (see <a href="Irp.html#Irp">Irp</a>) |
| and <code>.irpc</code> (see <a href="Irpc.html#Irpc">Irpc</a>) as well. |
| </p> |
| </dd> |
| <dt><code>.endm</code> |
| <a name="index-_002eendm"></a> |
| </dt> |
| <dd><a name="index-endm-directive"></a> |
| <p>Mark the end of a macro definition. |
| </p> |
| </dd> |
| <dt><code>.exitm</code> |
| <a name="index-_002eexitm"></a> |
| </dt> |
| <dd><a name="index-exitm-directive"></a> |
| <p>Exit early from the current macro definition. |
| </p> |
| <a name="index-number-of-macros-executed"></a> |
| <a name="index-macros_002c-count-executed"></a> |
| </dd> |
| <dt><code>\@</code> |
| <a name="index-_005c_0040"></a> |
| </dt> |
| <dd><p><code>as</code> maintains a counter of how many macros it has |
| executed in this pseudo-variable; you can copy that number to your |
| output with ‘<samp>\@</samp>’, but <em>only within a macro definition</em>. |
| </p> |
| </dd> |
| <dt><code>LOCAL <var>name</var> [ , … ]</code> |
| <a name="index-LOCAL-name-_005b-_002c-_2026-_005d-1"></a> |
| </dt> |
| <dd><p><em>Warning: <code>LOCAL</code> is only available if you select “alternate |
| macro syntax” with ‘<samp>--alternate</samp>’ or <code>.altmacro</code>.</em> |
| See <a href="Altmacro.html#Altmacro"><code>.altmacro</code></a>. |
| </p></dd> |
| </dl> |
| |
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