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191 lines
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<title>Blocks In Python - Debugging with GDB</title>
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<a name="Blocks-In-Python"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>,
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Previous: <a rel="previous" accesskey="p" href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>,
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<h5 class="subsubsection">23.2.2.26 Accessing blocks from Python</h5>
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<p><a name="index-blocks-in-python-2286"></a><a name="index-gdb_002eBlock-2287"></a>
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In <span class="sc">gdb</span>, 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 Python as a
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<code>gdb.Block</code>. Blocks rely on debugging information being
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available.
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<p>A frame has a block. Please see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>, for a more
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in-depth discussion of frames.
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<p>The outermost block is known as the <dfn>global block</dfn>. The global
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block typically holds public global variables and functions.
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<p>The block nested just inside the global block is the <dfn>static
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block</dfn>. The static block typically holds file-scoped variables and
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functions.
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<p><span class="sc">gdb</span> 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-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>).
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<p>Here is a short example that should help explain blocks:
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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>
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<p>A <code>gdb.Block</code> is iterable. The iterator returns the symbols
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(see <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>) local to the block. Python programs
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should not assume that a specific block object will always contain a
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given symbol, since changes in <span class="sc">gdb</span> features and
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infrastructure may cause symbols move across blocks in a symbol
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table.
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<p>The following block-related functions are available in the <code>gdb</code>
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module:
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<p><a name="index-gdb_002eblock_005ffor_005fpc-2288"></a>
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<div class="defun">
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— Function: <b>gdb.block_for_pc</b> (<var>pc</var>)<var><a name="index-gdb_002eblock_005ffor_005fpc-2289"></a></var><br>
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<blockquote><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>None</code>. This is identical to
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<code>gdb.current_progspace().block_for_pc(pc)</code> and is included for
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historical compatibility.
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</p></blockquote></div>
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<p>A <code>gdb.Block</code> object has the following methods:
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<div class="defun">
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— Function: <b>Block.is_valid</b> ()<var><a name="index-Block_002eis_005fvalid-2290"></a></var><br>
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<blockquote><p>Returns <code>True</code> if the <code>gdb.Block</code> object is valid,
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<code>False</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 method 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></blockquote></div>
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<p>A <code>gdb.Block</code> object has the following attributes:
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<div class="defun">
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— Variable: <b>Block.start</b><var><a name="index-Block_002estart-2291"></a></var><br>
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<blockquote><p>The start address of the block. This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.end</b><var><a name="index-Block_002eend-2292"></a></var><br>
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<blockquote><p>One past the last address that appears in the block. This attribute
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is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.function</b><var><a name="index-Block_002efunction-2293"></a></var><br>
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<blockquote><p>The name of the block represented as a <code>gdb.Symbol</code>. If the
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block is not named, then this attribute holds <code>None</code>. This
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attribute is not writable.
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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></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.superblock</b><var><a name="index-Block_002esuperblock-2294"></a></var><br>
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<blockquote><p>The block containing this block. If this parent block does not exist,
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this attribute holds <code>None</code>. This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.global_block</b><var><a name="index-Block_002eglobal_005fblock-2295"></a></var><br>
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<blockquote><p>The global block associated with this block. This attribute is not
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writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.static_block</b><var><a name="index-Block_002estatic_005fblock-2296"></a></var><br>
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<blockquote><p>The static block associated with this block. This attribute is not
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writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.is_global</b><var><a name="index-Block_002eis_005fglobal-2297"></a></var><br>
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<blockquote><p><code>True</code> if the <code>gdb.Block</code> object is a global block,
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<code>False</code> if not. This attribute is not
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writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Block.is_static</b><var><a name="index-Block_002eis_005fstatic-2298"></a></var><br>
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<blockquote><p><code>True</code> if the <code>gdb.Block</code> object is a static block,
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<code>False</code> if not. This attribute is not writable.
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</p></blockquote></div>
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