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<h3 class="section"><code>.comm </code><var>symbol</var><code> , </code><var>length</var><code> </code></h3>



   <p><code>.comm</code> declares a common symbol named <var>symbol</var>.  When linking, a

common symbol in one object file may be merged with a defined or common symbol

of the same name in another object file.  If <code>ld</code> does not see a

definition for the symbol-just one or more common symbols-then it will

allocate <var>length</var> bytes of uninitialized memory.  <var>length</var> must be an

absolute expression.  If <code>ld</code> sees multiple common symbols with

the same name, and they do not all have the same size, it will allocate space

using the largest size.



   <p>When using ELF, the <code>.comm</code> directive takes an optional third argument. 

This is the desired alignment of the symbol, specified as a byte boundary (for

example, an alignment of 16 means that the least significant 4 bits of the

address should be zero).  The alignment must be an absolute expression, and it

must be a power of two.  If <code>ld</code> allocates uninitialized memory

for the common symbol, it will use the alignment when placing the symbol.  If

no alignment is specified, <code>as</code> will set the alignment to the

largest power of two less than or equal to the size of the symbol, up to a

maximum of 16.



   <p>The syntax for <code>.comm</code> differs slightly on the HPPA.  The syntax is

<code></code><var>symbol</var><code> .comm, </code><var>length</var><code></code>; <var>symbol</var> is optional.



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