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<title>Asm Labels - Using the GNU Compiler Collection (GCC)</title>
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<h3 class="section">5.37 Controlling Names Used in Assembler Code</h3>

<p><a name="index-assembler-names-for-identifiers-2010"></a><a name="index-names-used-in-assembler-code-2011"></a><a name="index-identifiers_002c-names-in-assembler-code-2012"></a>
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:

<pre class="smallexample">     int foo asm ("myfoo") = 2;
</pre>
 <p class="noindent">This specifies that the name to be used for the variable <code>foo</code> in
the assembler code should be `<samp><span class="samp">myfoo</span></samp>' rather than the usual
`<samp><span class="samp">_foo</span></samp>'.

 <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>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>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:

<pre class="smallexample">     extern func () asm ("FUNC");

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

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