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| <title>Debugging with GDB: Blocks In Python</title> |
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| <a name="Blocks-In-Python"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Symbols-In-Python.html#Symbols-In-Python" accesskey="n" rel="next">Symbols In Python</a>, Previous: <a href="Frames-In-Python.html#Frames-In-Python" accesskey="p" rel="prev">Frames In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python 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> |
| <a name="Accessing-blocks-from-Python_002e"></a> |
| <h4 class="subsubsection">23.2.2.25 Accessing blocks from Python.</h4> |
| |
| <a name="index-blocks-in-python"></a> |
| <a name="index-gdb_002eBlock"></a> |
| |
| <p>In <small>GDB</small>, symbols are stored in blocks. A block corresponds |
| roughly to a scope in the source code. Blocks are organized |
| hierarchically, and are represented individually in Python as a |
| <code>gdb.Block</code>. Blocks rely on debugging information being |
| available. |
| </p> |
| <p>A frame has a block. Please see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>, for a more |
| in-depth discussion of frames. |
| </p> |
| <p>The outermost block is known as the <em>global block</em>. The global |
| block typically holds public global variables and functions. |
| </p> |
| <p>The block nested just inside the global block is the <em>static |
| block</em>. The static block typically holds file-scoped variables and |
| functions. |
| </p> |
| <p><small>GDB</small> provides a method to get a block’s superblock, but there |
| is currently no way to examine the sub-blocks of a block, or to |
| 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>). |
| </p> |
| <p>Here is a short example that should help explain blocks: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">/* This is in the global block. */ |
| int global; |
| |
| /* This is in the static block. */ |
| static int file_scope; |
| |
| /* 'function' is in the global block, and 'argument' is |
| in a block nested inside of 'function'. */ |
| int function (int argument) |
| { |
| /* 'local' is in a block inside 'function'. It may or may |
| not be in the same block as 'argument'. */ |
| int local; |
| |
| { |
| /* 'inner' is in a block whose superblock is the one holding |
| 'local'. */ |
| int inner; |
| |
| /* If this call is expanded by the compiler, you may see |
| a nested block here whose function is 'inline_function' |
| and whose superblock is the one holding 'inner'. */ |
| inline_function (); |
| } |
| } |
| </pre></div> |
| |
| <p>A <code>gdb.Block</code> is iterable. The iterator returns the symbols |
| (see <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>) local to the block. Python programs |
| should not assume that a specific block object will always contain a |
| given symbol, since changes in <small>GDB</small> features and |
| infrastructure may cause symbols move across blocks in a symbol |
| table. |
| </p> |
| <p>The following block-related functions are available in the <code>gdb</code> |
| module: |
| </p> |
| <a name="index-gdb_002eblock_005ffor_005fpc"></a> |
| <dl> |
| <dt><a name="index-gdb_002eblock_005ffor_005fpc-1"></a>Function: <strong>gdb.block_for_pc</strong> <em>(pc)</em></dt> |
| <dd><p>Return the innermost <code>gdb.Block</code> containing the given <var>pc</var> |
| value. If the block cannot be found for the <var>pc</var> value specified, |
| the function will return <code>None</code>. |
| </p></dd></dl> |
| |
| <p>A <code>gdb.Block</code> object has the following methods: |
| </p> |
| <dl> |
| <dt><a name="index-Block_002eis_005fvalid"></a>Function: <strong>Block.is_valid</strong> <em>()</em></dt> |
| <dd><p>Returns <code>True</code> if the <code>gdb.Block</code> object is valid, |
| <code>False</code> if not. A block object can become invalid if the block it |
| refers to doesn’t exist anymore in the inferior. All other |
| <code>gdb.Block</code> methods will throw an exception if it is invalid at |
| the time the method is called. The block’s validity is also checked |
| during iteration over symbols of the block. |
| </p></dd></dl> |
| |
| <p>A <code>gdb.Block</code> object has the following attributes: |
| </p> |
| <dl> |
| <dt><a name="index-Block_002estart"></a>Variable: <strong>Block.start</strong></dt> |
| <dd><p>The start address of the block. This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002eend"></a>Variable: <strong>Block.end</strong></dt> |
| <dd><p>The end address of the block. This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002efunction"></a>Variable: <strong>Block.function</strong></dt> |
| <dd><p>The name of the block represented as a <code>gdb.Symbol</code>. If the |
| block is not named, then this attribute holds <code>None</code>. This |
| attribute is not writable. |
| </p> |
| <p>For ordinary function blocks, the superblock is the static block. |
| However, you should note that it is possible for a function block to |
| have a superblock that is not the static block – for instance this |
| happens for an inlined function. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002esuperblock"></a>Variable: <strong>Block.superblock</strong></dt> |
| <dd><p>The block containing this block. If this parent block does not exist, |
| this attribute holds <code>None</code>. This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002eglobal_005fblock"></a>Variable: <strong>Block.global_block</strong></dt> |
| <dd><p>The global block associated with this block. This attribute is not |
| writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002estatic_005fblock"></a>Variable: <strong>Block.static_block</strong></dt> |
| <dd><p>The static block associated with this block. This attribute is not |
| writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002eis_005fglobal"></a>Variable: <strong>Block.is_global</strong></dt> |
| <dd><p><code>True</code> if the <code>gdb.Block</code> object is a global block, |
| <code>False</code> if not. This attribute is not |
| writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Block_002eis_005fstatic"></a>Variable: <strong>Block.is_static</strong></dt> |
| <dd><p><code>True</code> if the <code>gdb.Block</code> object is a static block, |
| <code>False</code> if not. This attribute is not writable. |
| </p></dd></dl> |
| |
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