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<a name="GNU-Assembler"></a>
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<a name="The-GNU-Assembler"></a>
<h3 class="section">1.2 The GNU Assembler</h3>


<p><small>GNU</small> <code>as</code> is really a family of assemblers.
If you use (or have used) the <small>GNU</small> assembler on one architecture, you
should find a fairly similar environment when you use it on another
architecture.  Each version has much in common with the others,
including object file formats, most assembler directives (often called
<em>pseudo-ops</em>) and assembler syntax.
</p>
<a name="index-purpose-of-GNU-assembler"></a>
<p><code>as</code> is primarily intended to assemble the output of the
<small>GNU</small> C compiler <code>gcc</code> for use by the linker
<code>ld</code>.  Nevertheless, we&rsquo;ve tried to make <code>as</code>
assemble correctly everything that other assemblers for the same
machine would assemble.
Any exceptions are documented explicitly (see <a href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>).
This doesn&rsquo;t mean <code>as</code> always uses the same syntax as another
assembler for the same architecture; for example, we know of several
incompatible versions of 680x0 assembly language syntax.
</p>

<p>Unlike older assemblers, <code>as</code> is designed to assemble a source
program in one pass of the source file.  This has a subtle impact on the
<kbd>.org</kbd> directive (see <a href="Org.html#Org"><code>.org</code></a>).
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