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<title>Using the GNU Compiler Collection (GCC): Asm Labels</title>

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<a name="Controlling-Names-Used-in-Assembler-Code"></a>
<h4 class="subsection">6.43.4 Controlling Names Used in Assembler Code</h4>
<a name="index-assembler-names-for-identifiers"></a>
<a name="index-names-used-in-assembler-code"></a>
<a name="index-identifiers_002c-names-in-assembler-code"></a>

<p>You can specify the name to be used in the assembler code for a C
function or variable by writing the <code>asm</code> (or <code>__asm__</code>)
keyword after the declarator as follows:
</p>
<div class="smallexample">
<pre class="smallexample">int foo asm (&quot;myfoo&quot;) = 2;
</pre></div>

<p>This specifies that the name to be used for the variable <code>foo</code> in
the assembler code should be &lsquo;<samp>myfoo</samp>&rsquo; rather than the usual
&lsquo;<samp>_foo</samp>&rsquo;.
</p>
<p>On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.
</p>
<p>It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see <a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>.  GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.
</p>
<p>You cannot use <code>asm</code> in this way in a function <em>definition</em>; but
you can get the same effect by writing a declaration for the function
before its definition and putting <code>asm</code> there, like this:
</p>
<div class="smallexample">
<pre class="smallexample">extern func () asm (&quot;FUNC&quot;);

func (x, y)
     int x, y;
/* <span class="roman">&hellip;</span> */
</pre></div>

<p>It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.  GCC
does not as yet have the ability to store static variables in registers.
Perhaps that will be added.
</p>
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