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| <title>Debugging with GDB: Frame Decorator API</title> |
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| <a name="Frame-Decorator-API"></a> |
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| <p> |
| Next: <a href="Writing-a-Frame-Filter.html#Writing-a-Frame-Filter" accesskey="n" rel="next">Writing a Frame Filter</a>, Previous: <a href="Frame-Filter-API.html#Frame-Filter-API" accesskey="p" rel="prev">Frame Filter API</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> |
| </div> |
| <hr> |
| <a name="Decorating-Frames_002e"></a> |
| <h4 class="subsubsection">23.2.2.10 Decorating Frames.</h4> |
| <a name="index-frame-decorator-api"></a> |
| |
| <p>Frame decorators are sister objects to frame filters (see <a href="Frame-Filter-API.html#Frame-Filter-API">Frame Filter API</a>). Frame decorators are applied by a frame filter and can |
| only be used in conjunction with frame filters. |
| </p> |
| <p>The purpose of a frame decorator is to customize the printed content |
| of each <code>gdb.Frame</code> in commands where frame filters are executed. |
| This concept is called decorating a frame. Frame decorators decorate |
| a <code>gdb.Frame</code> with Python code contained within each API call. |
| This separates the actual data contained in a <code>gdb.Frame</code> from |
| the decorated data produced by a frame decorator. This abstraction is |
| necessary to maintain integrity of the data contained in each |
| <code>gdb.Frame</code>. |
| </p> |
| <p>Frame decorators have a mandatory interface, defined below. |
| </p> |
| <p><small>GDB</small> already contains a frame decorator called |
| <code>FrameDecorator</code>. This contains substantial amounts of |
| boilerplate code to decorate the content of a <code>gdb.Frame</code>. It is |
| recommended that other frame decorators inherit and extend this |
| object, and only to override the methods needed. |
| </p> |
| <dl> |
| <dt><a name="index-FrameDecorator_002eelided"></a>Function: <strong>FrameDecorator.elided</strong> <em>(self)</em></dt> |
| <dd> |
| <p>The <code>elided</code> method groups frames together in a hierarchical |
| system. An example would be an interpreter, where multiple low-level |
| frames make up a single call in the interpreted language. In this |
| example, the frame filter would elide the low-level frames and present |
| a single high-level frame, representing the call in the interpreted |
| language, to the user. |
| </p> |
| <p>The <code>elided</code> function must return an iterable and this iterable |
| must contain the frames that are being elided wrapped in a suitable |
| frame decorator. If no frames are being elided this function may |
| return an empty iterable, or <code>None</code>. Elided frames are indented |
| from normal frames in a <code>CLI</code> backtrace, or in the case of |
| <code>GDB/MI</code>, are placed in the <code>children</code> field of the eliding |
| frame. |
| </p> |
| <p>It is the frame filter’s task to also filter out the elided frames from |
| the source iterator. This will avoid printing the frame twice. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002efunction"></a>Function: <strong>FrameDecorator.function</strong> <em>(self)</em></dt> |
| <dd> |
| <p>This method returns the name of the function in the frame that is to |
| be printed. |
| </p> |
| <p>This method must return a Python string describing the function, or |
| <code>None</code>. |
| </p> |
| <p>If this function returns <code>None</code>, <small>GDB</small> will not print any |
| data for this field. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002eaddress"></a>Function: <strong>FrameDecorator.address</strong> <em>(self)</em></dt> |
| <dd> |
| <p>This method returns the address of the frame that is to be printed. |
| </p> |
| <p>This method must return a Python numeric integer type of sufficient |
| size to describe the address of the frame, or <code>None</code>. |
| </p> |
| <p>If this function returns a <code>None</code>, <small>GDB</small> will not print |
| any data for this field. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002efilename"></a>Function: <strong>FrameDecorator.filename</strong> <em>(self)</em></dt> |
| <dd> |
| <p>This method returns the filename and path associated with this frame. |
| </p> |
| <p>This method must return a Python string containing the filename and |
| the path to the object file backing the frame, or <code>None</code>. |
| </p> |
| <p>If this function returns a <code>None</code>, <small>GDB</small> will not print |
| any data for this field. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002eline"></a>Function: <strong>FrameDecorator.line</strong> <em>(self):</em></dt> |
| <dd> |
| <p>This method returns the line number associated with the current |
| position within the function addressed by this frame. |
| </p> |
| <p>This method must return a Python integer type, or <code>None</code>. |
| </p> |
| <p>If this function returns a <code>None</code>, <small>GDB</small> will not print |
| any data for this field. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002eframe_005fargs"></a>Function: <strong>FrameDecorator.frame_args</strong> <em>(self)</em></dt> |
| <dd><a name="frame_005fargs"></a> |
| <p>This method must return an iterable, or <code>None</code>. Returning an |
| empty iterable, or <code>None</code> means frame arguments will not be |
| printed for this frame. This iterable must contain objects that |
| implement two methods, described here. |
| </p> |
| <p>This object must implement a <code>argument</code> method which takes a |
| single <code>self</code> parameter and must return a <code>gdb.Symbol</code> |
| (see <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>), or a Python string. The object must also |
| implement a <code>value</code> method which takes a single <code>self</code> |
| parameter and must return a <code>gdb.Value</code> (see <a href="Values-From-Inferior.html#Values-From-Inferior">Values From Inferior</a>), a Python value, or <code>None</code>. If the <code>value</code> |
| method returns <code>None</code>, and the <code>argument</code> method returns a |
| <code>gdb.Symbol</code>, <small>GDB</small> will look-up and print the value of |
| the <code>gdb.Symbol</code> automatically. |
| </p> |
| <p>A brief example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">class SymValueWrapper(): |
| |
| def __init__(self, symbol, value): |
| self.sym = symbol |
| self.val = value |
| |
| def value(self): |
| return self.val |
| |
| def symbol(self): |
| return self.sym |
| |
| class SomeFrameDecorator() |
| ... |
| ... |
| def frame_args(self): |
| args = [] |
| try: |
| block = self.inferior_frame.block() |
| except: |
| return None |
| |
| # Iterate over all symbols in a block. Only add |
| # symbols that are arguments. |
| for sym in block: |
| if not sym.is_argument: |
| continue |
| args.append(SymValueWrapper(sym,None)) |
| |
| # Add example synthetic argument. |
| args.append(SymValueWrapper(``foo'', 42)) |
| |
| return args |
| </pre></div> |
| </dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002eframe_005flocals"></a>Function: <strong>FrameDecorator.frame_locals</strong> <em>(self)</em></dt> |
| <dd> |
| <p>This method must return an iterable or <code>None</code>. Returning an |
| empty iterable, or <code>None</code> means frame local arguments will not be |
| printed for this frame. |
| </p> |
| <p>The object interface, the description of the various strategies for |
| reading frame locals, and the example are largely similar to those |
| described in the <code>frame_args</code> function, (see <a href="#frame_005fargs">The |
| frame filter frame_args function</a>). Below is a modified example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">class SomeFrameDecorator() |
| ... |
| ... |
| def frame_locals(self): |
| vars = [] |
| try: |
| block = self.inferior_frame.block() |
| except: |
| return None |
| |
| # Iterate over all symbols in a block. Add all |
| # symbols, except arguments. |
| for sym in block: |
| if sym.is_argument: |
| continue |
| vars.append(SymValueWrapper(sym,None)) |
| |
| # Add an example of a synthetic local variable. |
| vars.append(SymValueWrapper(``bar'', 99)) |
| |
| return vars |
| </pre></div> |
| </dd></dl> |
| |
| <dl> |
| <dt><a name="index-FrameDecorator_002einferior_005fframe"></a>Function: <strong>FrameDecorator.inferior_frame</strong> <em>(self):</em></dt> |
| <dd> |
| <p>This method must return the underlying <code>gdb.Frame</code> that this |
| frame decorator is decorating. <small>GDB</small> requires the underlying |
| frame for internal frame information to determine how to print certain |
| values when printing a frame. |
| </p></dd></dl> |
| |
| <hr> |
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| <p> |
| Next: <a href="Writing-a-Frame-Filter.html#Writing-a-Frame-Filter" accesskey="n" rel="next">Writing a Frame Filter</a>, Previous: <a href="Frame-Filter-API.html#Frame-Filter-API" accesskey="p" rel="prev">Frame Filter API</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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