<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
<html>
|
<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc.
|
|
Permission is granted to copy, distribute and/or modify this document
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
any later version published by the Free Software Foundation; with the
|
Invariant Sections being "Free Software" and "Free Software Needs
|
Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
|
and with the Back-Cover Texts as in (a) below.
|
|
(a) The FSF's Back-Cover Text is: "You are free to copy and modify
|
this GNU Manual. Buying copies from GNU Press supports the FSF in
|
developing GNU and promoting software freedom." -->
|
<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ -->
|
<head>
|
<title>Debugging with GDB: Frames In Python</title>
|
|
<meta name="description" content="Debugging with GDB: Frames In Python">
|
<meta name="keywords" content="Debugging with GDB: Frames In Python">
|
<meta name="resource-type" content="document">
|
<meta name="distribution" content="global">
|
<meta name="Generator" content="makeinfo">
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
<link href="index.html#Top" rel="start" title="Top">
|
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
<link href="Python-API.html#Python-API" rel="up" title="Python API">
|
<link href="Blocks-In-Python.html#Blocks-In-Python" rel="next" title="Blocks In Python">
|
<link href="Objfiles-In-Python.html#Objfiles-In-Python" rel="previous" title="Objfiles In Python">
|
<style type="text/css">
|
<!--
|
a.summary-letter {text-decoration: none}
|
blockquote.smallquotation {font-size: smaller}
|
div.display {margin-left: 3.2em}
|
div.example {margin-left: 3.2em}
|
div.indentedblock {margin-left: 3.2em}
|
div.lisp {margin-left: 3.2em}
|
div.smalldisplay {margin-left: 3.2em}
|
div.smallexample {margin-left: 3.2em}
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
div.smalllisp {margin-left: 3.2em}
|
kbd {font-style:oblique}
|
pre.display {font-family: inherit}
|
pre.format {font-family: inherit}
|
pre.menu-comment {font-family: serif}
|
pre.menu-preformatted {font-family: serif}
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
pre.smallexample {font-size: smaller}
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
pre.smalllisp {font-size: smaller}
|
span.nocodebreak {white-space:nowrap}
|
span.nolinebreak {white-space:nowrap}
|
span.roman {font-family:serif; font-weight:normal}
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
ul.no-bullet {list-style: none}
|
-->
|
</style>
|
|
|
</head>
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
<a name="Frames-In-Python"></a>
|
<div class="header">
|
<p>
|
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="previous">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>
|
</div>
|
<hr>
|
<a name="Accessing-inferior-stack-frames-from-Python"></a>
|
<h4 class="subsubsection">23.2.2.25 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>
|
|
<a name="index-gdb_002einvalidate_005fcached_005fframes"></a>
|
<dl>
|
<dt><a name="index-gdb_002einvalidate_005fcached_005fframes-1"></a>Function: <strong>gdb.invalidate_cached_frames</strong></dt>
|
<dd><p><small>GDB</small> internally keeps a cache of the frames that have been
|
unwound. This function invalidates this cache.
|
</p>
|
<p>This function should not generally be called by ordinary Python code.
|
It is documented for the sake of completeness.
|
</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>. If the frame
|
does not have a block – for example, if there is no debugging
|
information for the code in question – then this will throw an
|
exception.
|
</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>
|
|
<a name="gdbpy_005fframe_005fread_005fregister"></a><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. Returns a
|
<code>Gdb.Value</code> object. Throws an exception if <var>register</var> does
|
not exist. The <var>register</var> argument must be one of the following:
|
</p><ol>
|
<li> A string that is the name of a valid register (e.g., <code>'sp'</code> or
|
<code>'rax'</code>).
|
</li><li> A <code>gdb.RegisterDescriptor</code> object (see <a href="Registers-In-Python.html#Registers-In-Python">Registers In Python</a>).
|
</li><li> A <small>GDB</small> internal, platform specific number. Using these
|
numbers is supported for historic reasons, but is not recommended as
|
future changes to <small>GDB</small> could change the mapping between
|
numbers and the registers they represent, breaking any Python code
|
that uses the platform-specific numbers. The numbers are usually
|
found in the corresponding <samp><var>platform</var>-tdep.h</samp> file in the
|
<small>GDB</small> source tree.
|
</li></ol>
|
<p>Using a string to access registers will be slightly slower than the
|
other two methods as <small>GDB</small> must look up the mapping between
|
name and internal register number. If performance is critical
|
consider looking up and caching a <code>gdb.RegisterDescriptor</code>
|
object.
|
</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>
|
|
<hr>
|
<div class="header">
|
<p>
|
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="previous">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>
|
</div>
|
|
|
|
</body>
|
</html>
|
