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<title>STABS: Common Blocks</title>
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<a name="Common-Blocks"></a>
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Next: <a href="Statics.html#Statics" accesskey="n" rel="next">Statics</a>, Previous: <a href="Register-Variables.html#Register-Variables" accesskey="p" rel="previous">Register Variables</a>, Up: <a href="Variables.html#Variables" accesskey="u" rel="up">Variables</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Common-Blocks-1"></a>
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<h3 class="section">4.4 Common Blocks</h3>
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<p>A common block is a statically allocated section of memory which can be
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referred to by several source files. It may contain several variables.
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I believe Fortran is the only language with this feature.
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</p>
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<a name="index-N_005fBCOMM"></a>
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<a name="index-N_005fECOMM"></a>
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<a name="index-C_005fBCOMM"></a>
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<a name="index-C_005fECOMM"></a>
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<p>A <code>N_BCOMM</code> stab begins a common block and an <code>N_ECOMM</code> stab
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ends it. The only field that is significant in these two stabs is the
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string, which names a normal (non-debugging) symbol that gives the
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address of the common block. According to IBM documentation, only the
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<code>N_BCOMM</code> has the name of the common block (even though their
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compiler actually puts it both places).
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</p>
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<a name="index-N_005fECOML"></a>
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<a name="index-C_005fECOML"></a>
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<p>The stabs for the members of the common block are between the
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<code>N_BCOMM</code> and the <code>N_ECOMM</code>; the value of each stab is the
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offset within the common block of that variable. IBM uses the
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<code>C_ECOML</code> stab type, and there is a corresponding <code>N_ECOML</code>
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stab type, but Sun’s Fortran compiler uses <code>N_GSYM</code> instead. The
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variables within a common block use the ‘<samp>V</samp>’ symbol descriptor (I
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believe this is true of all Fortran variables). Other stabs (at least
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type declarations using <code>C_DECL</code>) can also be between the
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<code>N_BCOMM</code> and the <code>N_ECOMM</code>.
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