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| <title>Debugging with GDB: Frames In Python</title> |
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| <a name="Frames-In-Python"></a> |
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| Next: <a href="Blocks-In-Python.html#Blocks-In-Python" accesskey="n" rel="next">Blocks In Python</a>, Previous: <a href="Objfiles-In-Python.html#Objfiles-In-Python" accesskey="p" rel="prev">Objfiles 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-inferior-stack-frames-from-Python_002e"></a> |
| <h4 class="subsubsection">23.2.2.24 Accessing inferior stack frames from Python.</h4> |
| |
| <a name="index-frames-in-python"></a> |
| <p>When the debugged program stops, <small>GDB</small> is able to analyze its call |
| stack (see <a href="Frames.html#Frames">Stack frames</a>). The <code>gdb.Frame</code> class |
| represents a frame in the stack. A <code>gdb.Frame</code> object is only valid |
| while its corresponding frame exists in the inferior’s stack. If you try |
| to use an invalid frame object, <small>GDB</small> will throw a <code>gdb.error</code> |
| exception (see <a href="Exception-Handling.html#Exception-Handling">Exception Handling</a>). |
| </p> |
| <p>Two <code>gdb.Frame</code> objects can be compared for equality with the <code>==</code> |
| operator, like: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) python print gdb.newest_frame() == gdb.selected_frame () |
| True |
| </pre></div> |
| |
| <p>The following frame-related functions are available in the <code>gdb</code> module: |
| </p> |
| <a name="index-gdb_002eselected_005fframe"></a> |
| <dl> |
| <dt><a name="index-gdb_002eselected_005fframe-1"></a>Function: <strong>gdb.selected_frame</strong> <em>()</em></dt> |
| <dd><p>Return the selected frame object. (see <a href="Selection.html#Selection">Selecting a Frame</a>). |
| </p></dd></dl> |
| |
| <a name="index-gdb_002enewest_005fframe"></a> |
| <dl> |
| <dt><a name="index-gdb_002enewest_005fframe-1"></a>Function: <strong>gdb.newest_frame</strong> <em>()</em></dt> |
| <dd><p>Return the newest frame object for the selected thread. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-gdb_002eframe_005fstop_005freason_005fstring"></a>Function: <strong>gdb.frame_stop_reason_string</strong> <em>(reason)</em></dt> |
| <dd><p>Return a string explaining the reason why <small>GDB</small> stopped unwinding |
| frames, as expressed by the given <var>reason</var> code (an integer, see the |
| <code>unwind_stop_reason</code> method further down in this section). |
| </p></dd></dl> |
| |
| <p>A <code>gdb.Frame</code> object has the following methods: |
| </p> |
| <dl> |
| <dt><a name="index-Frame_002eis_005fvalid"></a>Function: <strong>Frame.is_valid</strong> <em>()</em></dt> |
| <dd><p>Returns true if the <code>gdb.Frame</code> object is valid, false if not. |
| A frame object can become invalid if the frame it refers to doesn’t |
| exist anymore in the inferior. All <code>gdb.Frame</code> methods will throw |
| an exception if it is invalid at the time the method is called. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002ename"></a>Function: <strong>Frame.name</strong> <em>()</em></dt> |
| <dd><p>Returns the function name of the frame, or <code>None</code> if it can’t be |
| obtained. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002earchitecture"></a>Function: <strong>Frame.architecture</strong> <em>()</em></dt> |
| <dd><p>Returns the <code>gdb.Architecture</code> object corresponding to the frame’s |
| architecture. See <a href="Architectures-In-Python.html#Architectures-In-Python">Architectures In Python</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002etype"></a>Function: <strong>Frame.type</strong> <em>()</em></dt> |
| <dd><p>Returns the type of the frame. The value can be one of: |
| </p><dl compact="compact"> |
| <dt><code>gdb.NORMAL_FRAME</code></dt> |
| <dd><p>An ordinary stack frame. |
| </p> |
| </dd> |
| <dt><code>gdb.DUMMY_FRAME</code></dt> |
| <dd><p>A fake stack frame that was created by <small>GDB</small> when performing an |
| inferior function call. |
| </p> |
| </dd> |
| <dt><code>gdb.INLINE_FRAME</code></dt> |
| <dd><p>A frame representing an inlined function. The function was inlined |
| into a <code>gdb.NORMAL_FRAME</code> that is older than this one. |
| </p> |
| </dd> |
| <dt><code>gdb.TAILCALL_FRAME</code></dt> |
| <dd><p>A frame representing a tail call. See <a href="Tail-Call-Frames.html#Tail-Call-Frames">Tail Call Frames</a>. |
| </p> |
| </dd> |
| <dt><code>gdb.SIGTRAMP_FRAME</code></dt> |
| <dd><p>A signal trampoline frame. This is the frame created by the OS when |
| it calls into a signal handler. |
| </p> |
| </dd> |
| <dt><code>gdb.ARCH_FRAME</code></dt> |
| <dd><p>A fake stack frame representing a cross-architecture call. |
| </p> |
| </dd> |
| <dt><code>gdb.SENTINEL_FRAME</code></dt> |
| <dd><p>This is like <code>gdb.NORMAL_FRAME</code>, but it is only used for the |
| newest frame. |
| </p></dd> |
| </dl> |
| </dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eunwind_005fstop_005freason"></a>Function: <strong>Frame.unwind_stop_reason</strong> <em>()</em></dt> |
| <dd><p>Return an integer representing the reason why it’s not possible to find |
| more frames toward the outermost frame. Use |
| <code>gdb.frame_stop_reason_string</code> to convert the value returned by this |
| function to a string. The value can be one of: |
| </p> |
| <dl compact="compact"> |
| <dt><code>gdb.FRAME_UNWIND_NO_REASON</code></dt> |
| <dd><p>No particular reason (older frames should be available). |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_NULL_ID</code></dt> |
| <dd><p>The previous frame’s analyzer returns an invalid result. This is no |
| longer used by <small>GDB</small>, and is kept only for backward |
| compatibility. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_OUTERMOST</code></dt> |
| <dd><p>This frame is the outermost. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_UNAVAILABLE</code></dt> |
| <dd><p>Cannot unwind further, because that would require knowing the |
| values of registers or memory that have not been collected. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_INNER_ID</code></dt> |
| <dd><p>This frame ID looks like it ought to belong to a NEXT frame, |
| but we got it for a PREV frame. Normally, this is a sign of |
| unwinder failure. It could also indicate stack corruption. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_SAME_ID</code></dt> |
| <dd><p>This frame has the same ID as the previous one. That means |
| that unwinding further would almost certainly give us another |
| frame with exactly the same ID, so break the chain. Normally, |
| this is a sign of unwinder failure. It could also indicate |
| stack corruption. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_NO_SAVED_PC</code></dt> |
| <dd><p>The frame unwinder did not find any saved PC, but we needed |
| one to unwind further. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_MEMORY_ERROR</code></dt> |
| <dd><p>The frame unwinder caused an error while trying to access memory. |
| </p> |
| </dd> |
| <dt><code>gdb.FRAME_UNWIND_FIRST_ERROR</code></dt> |
| <dd><p>Any stop reason greater or equal to this value indicates some kind |
| of error. This special value facilitates writing code that tests |
| for errors in unwinding in a way that will work correctly even if |
| the list of the other values is modified in future <small>GDB</small> |
| versions. Using it, you could write: |
| </p><div class="smallexample"> |
| <pre class="smallexample">reason = gdb.selected_frame().unwind_stop_reason () |
| reason_str = gdb.frame_stop_reason_string (reason) |
| if reason >= gdb.FRAME_UNWIND_FIRST_ERROR: |
| print "An error occured: %s" % reason_str |
| </pre></div> |
| </dd> |
| </dl> |
| |
| </dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002epc"></a>Function: <strong>Frame.pc</strong> <em>()</em></dt> |
| <dd><p>Returns the frame’s resume address. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eblock"></a>Function: <strong>Frame.block</strong> <em>()</em></dt> |
| <dd><p>Return the frame’s code block. See <a href="Blocks-In-Python.html#Blocks-In-Python">Blocks In Python</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002efunction"></a>Function: <strong>Frame.function</strong> <em>()</em></dt> |
| <dd><p>Return the symbol for the function corresponding to this frame. |
| See <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eolder"></a>Function: <strong>Frame.older</strong> <em>()</em></dt> |
| <dd><p>Return the frame that called this frame. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002enewer"></a>Function: <strong>Frame.newer</strong> <em>()</em></dt> |
| <dd><p>Return the frame called by this frame. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002efind_005fsal"></a>Function: <strong>Frame.find_sal</strong> <em>()</em></dt> |
| <dd><p>Return the frame’s symtab and line object. |
| See <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eread_005fregister"></a>Function: <strong>Frame.read_register</strong> <em>(register)</em></dt> |
| <dd><p>Return the value of <var>register</var> in this frame. The <var>register</var> |
| argument must be a string (e.g., <code>'sp'</code> or <code>'rax'</code>). |
| Returns a <code>Gdb.Value</code> object. Throws an exception if <var>register</var> |
| does not exist. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eread_005fvar"></a>Function: <strong>Frame.read_var</strong> <em>(variable <span class="roman">[</span>, block<span class="roman">]</span>)</em></dt> |
| <dd><p>Return the value of <var>variable</var> in this frame. If the optional |
| argument <var>block</var> is provided, search for the variable from that |
| block; otherwise start at the frame’s current block (which is |
| determined by the frame’s current program counter). The <var>variable</var> |
| argument must be a string or a <code>gdb.Symbol</code> object; <var>block</var> must be a |
| <code>gdb.Block</code> object. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Frame_002eselect"></a>Function: <strong>Frame.select</strong> <em>()</em></dt> |
| <dd><p>Set this frame to be the selected frame. See <a href="Stack.html#Stack">Examining the |
| Stack</a>. |
| </p></dd></dl> |
| |
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