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| <h5 class="subsubsection">23.2.2.26 Accessing blocks from Python</h5> |
| |
| <p><a name="index-blocks-in-python-2286"></a><a name="index-gdb_002eBlock-2287"></a> |
| In <span class="sc">gdb</span>, 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>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>The outermost block is known as the <dfn>global block</dfn>. The global |
| block typically holds public global variables and functions. |
| |
| <p>The block nested just inside the global block is the <dfn>static |
| block</dfn>. The static block typically holds file-scoped variables and |
| functions. |
| |
| <p><span class="sc">gdb</span> 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>Here is a short example that should help explain blocks: |
| |
| <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> |
| <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 <span class="sc">gdb</span> features and |
| infrastructure may cause symbols move across blocks in a symbol |
| table. |
| |
| <p>The following block-related functions are available in the <code>gdb</code> |
| module: |
| |
| <p><a name="index-gdb_002eblock_005ffor_005fpc-2288"></a> |
| |
| <div class="defun"> |
| — Function: <b>gdb.block_for_pc</b> (<var>pc</var>)<var><a name="index-gdb_002eblock_005ffor_005fpc-2289"></a></var><br> |
| <blockquote><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>. This is identical to |
| <code>gdb.current_progspace().block_for_pc(pc)</code> and is included for |
| historical compatibility. |
| </p></blockquote></div> |
| |
| <p>A <code>gdb.Block</code> object has the following methods: |
| |
| <div class="defun"> |
| — Function: <b>Block.is_valid</b> ()<var><a name="index-Block_002eis_005fvalid-2290"></a></var><br> |
| <blockquote><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></blockquote></div> |
| |
| <p>A <code>gdb.Block</code> object has the following attributes: |
| |
| <div class="defun"> |
| — Variable: <b>Block.start</b><var><a name="index-Block_002estart-2291"></a></var><br> |
| <blockquote><p>The start address of the block. This attribute is not writable. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.end</b><var><a name="index-Block_002eend-2292"></a></var><br> |
| <blockquote><p>One past the last address that appears in the block. This attribute |
| is not writable. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.function</b><var><a name="index-Block_002efunction-2293"></a></var><br> |
| <blockquote><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>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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.superblock</b><var><a name="index-Block_002esuperblock-2294"></a></var><br> |
| <blockquote><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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.global_block</b><var><a name="index-Block_002eglobal_005fblock-2295"></a></var><br> |
| <blockquote><p>The global block associated with this block. This attribute is not |
| writable. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.static_block</b><var><a name="index-Block_002estatic_005fblock-2296"></a></var><br> |
| <blockquote><p>The static block associated with this block. This attribute is not |
| writable. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.is_global</b><var><a name="index-Block_002eis_005fglobal-2297"></a></var><br> |
| <blockquote><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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Block.is_static</b><var><a name="index-Block_002eis_005fstatic-2298"></a></var><br> |
| <blockquote><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></blockquote></div> |
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