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<title>Debugging with GDB: Blocks In Guile</title>
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<a name="Blocks-In-Guile"></a>
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<div class="header">
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<p>
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Next: <a href="Symbols-In-Guile.html#Symbols-In-Guile" accesskey="n" rel="next">Symbols In Guile</a>, Previous: <a href="Frames-In-Guile.html#Frames-In-Guile" accesskey="p" rel="previous">Frames In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Accessing-blocks-from-Guile_002e"></a>
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<h4 class="subsubsection">23.3.3.16 Accessing blocks from Guile.</h4>
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<a name="index-blocks-in-guile"></a>
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<a name="index-_003cgdb_003ablock_003e"></a>
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<p>In <small>GDB</small>, symbols are stored in blocks. A block corresponds
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roughly to a scope in the source code. Blocks are organized
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hierarchically, and are represented individually in Guile as an object
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of type <code><gdb:block></code>. Blocks rely on debugging information being
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available.
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</p>
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<p>A frame has a block. Please see <a href="Frames-In-Guile.html#Frames-In-Guile">Frames In Guile</a>, for a more
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in-depth discussion of frames.
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</p>
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<p>The outermost block is known as the <em>global block</em>. The global
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block typically holds public global variables and functions.
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</p>
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<p>The block nested just inside the global block is the <em>static
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block</em>. The static block typically holds file-scoped variables and
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functions.
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</p>
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<p><small>GDB</small> provides a method to get a block’s superblock, but there
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is currently no way to examine the sub-blocks of a block, or to
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iterate over all the blocks in a symbol table (see <a href="Symbol-Tables-In-Guile.html#Symbol-Tables-In-Guile">Symbol Tables In Guile</a>).
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</p>
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<p>Here is a short example that should help explain blocks:
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</p>
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<div class="smallexample">
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<pre class="smallexample">/* This is in the global block. */
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int global;
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/* This is in the static block. */
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static int file_scope;
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/* 'function' is in the global block, and 'argument' is
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in a block nested inside of 'function'. */
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int function (int argument)
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{
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/* 'local' is in a block inside 'function'. It may or may
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not be in the same block as 'argument'. */
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int local;
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{
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/* 'inner' is in a block whose superblock is the one holding
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'local'. */
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int inner;
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/* If this call is expanded by the compiler, you may see
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a nested block here whose function is 'inline_function'
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and whose superblock is the one holding 'inner'. */
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inline_function ();
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}
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}
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</pre></div>
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<p>The following block-related procedures are provided by the
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<code>(gdb)</code> module:
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</p>
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<dl>
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<dt><a name="index-block_003f"></a>Scheme Procedure: <strong>block?</strong> <em>object</em></dt>
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<dd><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:block></code> object.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dvalid_003f"></a>Scheme Procedure: <strong>block-valid?</strong> <em>block</em></dt>
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<dd><p>Returns <code>#t</code> if <code><gdb:block></code> <var>block</var> is valid,
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<code>#f</code> if not. A block object can become invalid if the block it
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refers to doesn’t exist anymore in the inferior. All other
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<code><gdb:block></code> methods will throw an exception if it is invalid at
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the time the procedure is called. The block’s validity is also checked
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during iteration over symbols of the block.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dstart"></a>Scheme Procedure: <strong>block-start</strong> <em>block</em></dt>
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<dd><p>Return the start address of <code><gdb:block></code> <var>block</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dend"></a>Scheme Procedure: <strong>block-end</strong> <em>block</em></dt>
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<dd><p>Return the end address of <code><gdb:block></code> <var>block</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dfunction"></a>Scheme Procedure: <strong>block-function</strong> <em>block</em></dt>
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<dd><p>Return the name of <code><gdb:block></code> <var>block</var> represented as a
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<code><gdb:symbol></code> object.
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If the block is not named, then <code>#f</code> is returned.
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</p>
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<p>For ordinary function blocks, the superblock is the static block.
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However, you should note that it is possible for a function block to
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have a superblock that is not the static block – for instance this
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happens for an inlined function.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dsuperblock"></a>Scheme Procedure: <strong>block-superblock</strong> <em>block</em></dt>
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<dd><p>Return the block containing <code><gdb:block></code> <var>block</var>.
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If the parent block does not exist, then <code>#f</code> is returned.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dglobal_002dblock"></a>Scheme Procedure: <strong>block-global-block</strong> <em>block</em></dt>
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<dd><p>Return the global block associated with <code><gdb:block></code> <var>block</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dstatic_002dblock"></a>Scheme Procedure: <strong>block-static-block</strong> <em>block</em></dt>
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<dd><p>Return the static block associated with <code><gdb:block></code> <var>block</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dglobal_003f"></a>Scheme Procedure: <strong>block-global?</strong> <em>block</em></dt>
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<dd><p>Return <code>#t</code> if <code><gdb:block></code> <var>block</var> is a global block.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dstatic_003f"></a>Scheme Procedure: <strong>block-static?</strong> <em>block</em></dt>
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<dd><p>Return <code>#t</code> if <code><gdb:block></code> <var>block</var> is a static block.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dsymbols"></a>Scheme Procedure: <strong>block-symbols</strong></dt>
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<dd><p>Return a list of all symbols (as <gdb:symbol> objects) in
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<code><gdb:block></code> <var>block</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-make_002dblock_002dsymbols_002diterator"></a>Scheme Procedure: <strong>make-block-symbols-iterator</strong> <em>block</em></dt>
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<dd><p>Return an object of type <code><gdb:iterator></code> that will iterate
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over all symbols of the block.
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Guile programs should not assume that a specific block object will
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always contain a given symbol, since changes in <small>GDB</small> features and
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infrastructure may cause symbols move across blocks in a symbol table.
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See <a href="Iterators-In-Guile.html#Iterators-In-Guile">Iterators In Guile</a>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-block_002dsymbols_002dprogress_003f"></a>Scheme Procedure: <strong>block-symbols-progress?</strong></dt>
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<dd><p>Return #t if the object is a <gdb:block-symbols-progress> object.
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This object would be obtained from the <code>progress</code> element of the
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<code><gdb:iterator></code> object returned by <code>make-block-symbols-iterator</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-lookup_002dblock"></a>Scheme Procedure: <strong>lookup-block</strong> <em>pc</em></dt>
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<dd><p>Return the innermost <code><gdb:block></code> containing the given <var>pc</var>
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value. If the block cannot be found for the <var>pc</var> value specified,
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the function will return <code>#f</code>.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Symbols-In-Guile.html#Symbols-In-Guile" accesskey="n" rel="next">Symbols In Guile</a>, Previous: <a href="Frames-In-Guile.html#Frames-In-Guile" accesskey="p" rel="previous">Frames In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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