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debuggercdi/com.nokia.carbide.cpp.debug.crashdebugger/html/DebuggingInformation/CrashDebuggerCallStack.guide05.html
author timkelly
Tue, 04 May 2010 09:39:10 -0500
branchRCL_2_4
changeset 1325 98aebbb322f3
parent 990 5d016a880824
permissions -rw-r--r--
Fix bug 11210. NPEs when editing SBSv2 config tab data on old SBSv2 build configs. Now allows saving SBSv2 variant data for old SBSv2 configs (i.e. before we display the build alias in the config name)
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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	"http://www.w3.org/TR/html4/loose.dtd">
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	<html><head>
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	<title>Walking through the Call Stack</title>
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	<link href="sysdoc-eclipse.css" type="text/css" rel="stylesheet" >
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	<link href="sysdoc-eclipse.css" type="text/css" rel="stylesheet" >
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	<link href="../../book.css" type="text/css" rel="stylesheet" >
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<div class="Head1">
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  <h2>Walking through the Call Stack</h2>
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</div>
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<div>
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<p>The heuristic method is quick but produces lots of false positives.
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Another option is to manually reconstitute the call stack from the memory dump.
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This is relatively easy for debug builds because GCC uses R11 as a frame
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pointer (FP) and generates the same prologue/epilogue for every
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function.</p>
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<p>For release builds, there is no generic solution. It is necessary
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to check the generated assembler code as there is no standard prologue/epilogue
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and R11 is not used as frame pointer.</p>
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<p>A typical prologue for a debug ARM function looks like this:</p>
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<p class="CodeBlock">mov&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ip, sp<br>stmfd&nbsp;&nbsp;&nbsp;sp!, {fp, ip, lr, pc}<br>sub&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fp, ip, #4&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* FP now points to base of stack frame */<br>sub&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sp, sp, #16&nbsp;&nbsp;&nbsp;&nbsp;/* space for local variables */</p>
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<p>noting that: SP = R13, FP = R11, IP
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= R12, LR = R14, and PC = R15.</p>
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<p>This code creates the following stack frame:</p>
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<div class="Figure">
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<p class="Image"><a name=""><img src="CrashDebuggerStackFrame-01.gif" alt=""  border="0"></a></p>
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</div>
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<p>Looking at the example session listed in when
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<a href="CrashDebuggerCallStack.guide.html" title="Examining the call stack / Tracing through the stack heuristically">tracing through the stack heuristically</a>. in which the crash is due to a panic, the FP value is the
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R11 value; this is 0x6571de70. This gives us the innermost stack
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frame:</p>
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<p class="CodeBlock">6571de64:&nbsp;&nbsp;&nbsp;e8 de 71 65 &lt;------------- pointer to previous stack frame <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;74 de 71 65 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;74 fb 16 f8 &lt;------------- Saved return address <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;88 28 03 f8 &lt;------------- FP points to this word</p>
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<p>Looking up the saved return address, 0xf816fb74, in
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the symbol file shows that the current function was called from
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DDmaChannel::DoCreate().</p>
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<p class="CodeBlock">f816fb50    0198    DDmaTestChannel::DoCreate(int, TDesC8 const *, TVersion const &amp;)<br>f816fce8    007c    DDmaTestChannel::~DDmaTestChannel(void)<br>f816fd64    0294    DDmaTestChannel::Request(int, void *, void *)</p>
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<p>Using the pointer to the previous stack frame saved into the
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current frame, we can decode the next frame:</p>
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<p class="CodeBlock">6571ded4:&nbsp;&nbsp;&nbsp;1c c4 03 64 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f8 02 00 64 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;10 df 71 65 &lt;------------- pointer to previous stack frame <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ec de 71 65 <br><br>6571dee4:&nbsp;&nbsp;&nbsp;84 da 01 f8 &lt;------------- saved return address <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5c fb 16 f8 &lt;------------- start of second stack frame <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;00 4e 40 00 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;00 00 00 00 </p>
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<p>Looking up the saved return address, 0xf801da84, in
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the symbol file shows that DDmaTestChannel::DoCreate() was called
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from DLogicalDevice::ChannelCreate().</p>
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<p class="CodeBlock">f801d9b4    00f8    DLogicalDevice::ChannelCreate(DLogicalChannelBase *&amp;, TChannelCreateInfo &amp;)<br>f801daac    01b8    ExecHandler::ChannelCreate(TDesC8 const &amp;, TChannelCreateInfo &amp;, int)<br>f801dc64    00e4    ExecHandler::ChannelRequest(DLogicalChannelBase *, int, void *, void *)</p>
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<p>And here is the third stack frame:</p>
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<p class="CodeBlock">6571df04:&nbsp;&nbsp;&nbsp;d4 df 71 65 &lt;------------- pointer to previous stack frame <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14 df 71 65 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;e0 db 01 f8 &lt;------------- saved return address <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c0 d9 01 f8 &lt;------------- start of third stack frame </p>
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<p>So DLogicalDevice::ChannelCreate() was called from
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ExecHandler::ChannelCreate().</p>
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<p>Note that this mechanical way of walking the stack is valid only
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for debug functions. For release functions, it is necessary to study the code
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generated by the compiler.</p>
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<p>For completness, this is a typical prologue for a debug THUMB
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function:</p>
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<p class="CodeBlock">push&nbsp;&nbsp;&nbsp;&nbsp;{ r7, lr }<br>sub&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sp, #28<br>add&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;r7, sp, #12 /* R7 is THUMB frame pointer */</p>
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<p>and this creates the following stack frame:</p>
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<div class="Figure">
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<p class="Image"><a name=""><img src="CrashDebuggerStackFrame-02.gif" alt=""  border="0"></a></p>
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</div>
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<p>A call stack can mix ARM and THUMB frames. Odd return addresses are
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used for THUMB code and even ones for ARM code.</p>
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</div>













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<h5>Related tasks</h5>













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<ul>













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  <li><a href="CrashDebuggerCallStack.guide02.html">General Points</a></li>













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  <li><a href="CrashDebuggerCallStack.guide03.html">Finding the Stack</a></li>













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  <li><a href="CrashDebuggerCallStack.guide04.html">Tracing through the Call Stack Heuristically</a></li>













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</ul>













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<div id="footer">Copyright &copy; 2010 Nokia Corporation and/or its subsidiary(-ies). All rights reserved. <br>License: <a href="http://www.eclipse.org/legal/epl-v10.html">http://www.eclipse.org/legal/epl-v10.html</a></div>













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	   </body>













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	   </html>








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fb279309251b
DP tools release version Revision: 200912



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FCL/sftools/dev/ide/carbidecpp