http://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&feed=atom&action=historyStack Analysis - Revision history2024-03-29T12:02:00ZRevision history for this page on the wikiMediaWiki 1.31.14http://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2745&oldid=prevSissou: /* What is Stack Depth Analysis? */2009-11-12T06:51:50Z<p><span dir="auto"><span class="autocomment">What is Stack Depth Analysis?</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 06:51, 12 November 2009</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= What is Stack Depth Analysis? =</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= What is Stack Depth Analysis? =</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Calling a function or handling an interrupt causes ''stack memory'' to be allocated.  If the stack memory region -- the portion of a mote's RAM reserved for the stack -- is not large enough to hold the stack, a ''stack overflow'' occurs.  Stack overflow leads to corrupted RAM and subsequently to difficult, non-deterministic node failures.  These failures cannot be reproduced in TOSSIM, though they can be found in a CPU-level simulator such as Avrora or MSPsim.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Calling a function or handling an interrupt causes ''stack memory'' to be allocated.  If the stack memory region -- the portion of a mote's RAM reserved for the stack -- is not large enough to hold the stack, a ''stack overflow'' occurs.  Stack overflow leads to corrupted RAM and subsequently to difficult, non-deterministic node failures.  These failures cannot be reproduced in <ins class="diffchange diffchange-inline">[[</ins>TOSSIM<ins class="diffchange diffchange-inline">]]</ins>, though they can be found in a CPU-level simulator such as <ins class="diffchange diffchange-inline">[[</ins>Avrora<ins class="diffchange diffchange-inline">]] </ins>or <ins class="diffchange diffchange-inline">[[</ins>MSPsim<ins class="diffchange diffchange-inline">]]</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>We call an application ''stack safe'' if every stack memory region is large enough to contain the worst-case size of its stack.  A TinyOS application that does not use TOSThreads has a single stack and its size can be computed like this:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>We call an application ''stack safe'' if every stack memory region is large enough to contain the worst-case size of its stack.  A TinyOS application that does not use TOSThreads has a single stack and its size can be computed like this:</div></td></tr>
</table>Sissouhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2423&oldid=prevJohnRegehr: /* Reducing Stack Memory Usage */2009-04-25T04:51:40Z<p><span dir="auto"><span class="autocomment">Reducing Stack Memory Usage</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 04:51, 25 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l240" >Line 240:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks use stack memory more efficiently than interrupts do.  This is also good programming practice.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks use stack memory more efficiently than interrupts do.  This is also good programming practice.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining<ins class="diffchange diffchange-inline">.  An important way to break up a long call chain in TinyOS is to post a task to do something, rather than calling the code directly</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Understand the stack memory requirements of library code called by your application.  tos-ramsize can tell you about this if you crank up the verbosity.  Or just run "objdump -d" on your elf file and look at the library code directly.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Understand the stack memory requirements of library code called by your application.  tos-ramsize can tell you about this if you crank up the verbosity.  Or just run "objdump -d" on your elf file and look at the library code directly.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid creating an excessive number of threads, if using TOSThreads.  Unlike tasks, which share stack memory, threads have separate stacks.  Furthermore, each thread requires a large enough stack to support a full nesting of interrupts without overflowing onto the next thread's stack.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid creating an excessive number of threads, if using TOSThreads.  Unlike tasks, which share stack memory, threads have separate stacks.  Furthermore, each thread requires a large enough stack to support a full nesting of interrupts without overflowing onto the next thread's stack.</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2407&oldid=prevJohnRegehr: /* Who Cares? */2009-04-21T15:19:39Z<p><span dir="auto"><span class="autocomment">Who Cares?</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 15:19, 21 April 2009</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>To be sure, many of the applications from <tt>tinyos-2.x/apps</tt> are totally safe from stack overflow.  On the other hand, here are some concrete situations in which you should care about worst-case stack memory usage:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>To be sure, many of the applications from <tt>tinyos-2.x/apps</tt> are totally safe from stack overflow.  On the other hand, here are some concrete situations in which you should care about worst-case stack memory usage:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* If your application is short on RAM (for example, it statically allocates 3.5 KB or more on a MicaZ) and you are seeing spurious node failures, stack overflow should be on your short list of potential root causes<del class="diffchange diffchange-inline">.  This is particularly true of applications that make use of TOSThreads</del>.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* If your application is short on RAM (for example, it statically allocates 3.5 KB or more on a MicaZ) and you are seeing spurious node failures, stack overflow should be on your short list of potential root causes.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* If your application could benefit from additional RAM allocation, for example to create deeper packet queues or larger data buffers, stack depth analysis offers a quick way to compute how much extra RAM you may safely allocate.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* If your application could benefit from additional RAM allocation, for example to create deeper packet queues or larger data buffers, stack depth analysis offers a quick way to compute how much extra RAM you may safely allocate.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* If your application uses a heap, stack depth analysis makes it easy to choose a safe upper bound on the heap region.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* If your application uses a heap, stack depth analysis makes it easy to choose a safe upper bound on the heap region.</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2406&oldid=prevJohnRegehr: /* What is Stack Depth Analysis? */2009-04-21T15:17:55Z<p><span dir="auto"><span class="autocomment">What is Stack Depth Analysis?</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 15:17, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l13" >Line 13:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The ''worst observed stack depth'' is the largest stack size seen during testing.  Testing methods include observing the maximum extent of the stack using a simulator, periodically printing the value of the stack pointer from an interrupt handler, or filling the stack with known values and seeing how many get overwritten.  All testing-based techniques are unsafe in the sense that they can only provide a lower bound on the system's worst case stack memory usage.  The ''true worst case stack depth'' of a computer program is uncomputable; the best we can do is to try to narrow the gap between the lower and upper bounds.  Stack depth analysis -- the subject of this document -- is a technique for computing a safe upper bound on the worst-case stack memory requirements of an application.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The ''worst observed stack depth'' is the largest stack size seen during testing.  Testing methods include observing the maximum extent of the stack using a simulator, periodically printing the value of the stack pointer from an interrupt handler, or filling the stack with known values and seeing how many get overwritten.  All testing-based techniques are unsafe in the sense that they can only provide a lower bound on the system's worst case stack memory usage.  The ''true worst case stack depth'' of a computer program is uncomputable; the best we can do is to try to narrow the gap between the lower and upper bounds.  Stack depth analysis -- the subject of this document -- is a technique for computing a safe upper bound on the worst-case stack memory requirements of an application.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>'''Note:''' Stack overflow -- as the term is used here -- is a <del class="diffchange diffchange-inline">distinct </del>problem from buffer overflow (aka buffer overrun, stack-based buffer overflow).  The latter can be prevented using standard safe language techniques.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>'''Note:''' Stack overflow -- as the term is used here -- is a <ins class="diffchange diffchange-inline">totally different </ins>problem from buffer overflow (aka buffer overrun, stack-based buffer overflow).  The latter can be prevented using standard safe language techniques.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= Who Cares? =</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= Who Cares? =</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2405&oldid=prevJohnRegehr: /* Reducing Stack Memory Usage */2009-04-21T15:06:01Z<p><span dir="auto"><span class="autocomment">Reducing Stack Memory Usage</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 15:06, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l238" >Line 238:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>As a programmer, there are a few easy things you can do to ensure that stack memory is not wasted:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>As a programmer, there are a few easy things you can do to ensure that stack memory is not wasted:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Make interrupt handlers atomic whenever possible.  This is good programming practice anyway.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Make interrupt handlers atomic whenever possible.  This is good programming practice anyway.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks <del class="diffchange diffchange-inline">make very efficient </del>use <del class="diffchange diffchange-inline">of </del>stack memory.  This is also good programming practice.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks use stack memory <ins class="diffchange diffchange-inline">more efficiently than interrupts do</ins>.  This is also good programming practice.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining.</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2404&oldid=prevJohnRegehr: /* How Stack Analysis Works */2009-04-21T04:16:38Z<p><span dir="auto"><span class="autocomment">How Stack Analysis Works</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<tr class="diff-title" lang="en">
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 04:16, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l183" >Line 183:</td>
<td colspan="2" class="diff-lineno">Line 183:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>One might argue that the worst-case stack depth has a low probability of being reached in practice.  In general, when multiple interrupt handlers are involved, this is true.  The wrong way to reclaim some RAM is to optimistically assume that the worst case will never happen.  The right ways to reclaim some RAM are discussed below.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>One might argue that the worst-case stack depth has a low probability of being reached in practice.  In general, when multiple interrupt handlers are involved, this is true.  The wrong way to reclaim some RAM is to optimistically assume that the worst case will never happen.  The right ways to reclaim some RAM are discussed below.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>In some cases, tos-ramsize is <del class="diffchange diffchange-inline">truly </del>conservative, returning <del class="diffchange diffchange-inline">an upper bound that </del>is <del class="diffchange diffchange-inline">too high</del>. <del class="diffchange diffchange-inline"> These include:</del></div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>In some cases, tos-ramsize <ins class="diffchange diffchange-inline">really </ins>is <ins class="diffchange diffchange-inline">overly </ins>conservative<ins class="diffchange diffchange-inline">.  For example:</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">* Two interrupt handlers may never be runnable at the same time</ins>, <ins class="diffchange diffchange-inline">for example because they service hardware devices that cannot be used concurrently.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">* A nonatomic interrupt may only enable interrupts just before </ins>returning<ins class="diffchange diffchange-inline">, at a point where it </ins>is <ins class="diffchange diffchange-inline">using almost no stack memory</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Some functions and/or interrupt handlers may be dead code.  They will contribute to estimated stack depth but not to the actual worst-case stack depth.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Some functions and/or interrupt handlers may be dead code.  They will contribute to estimated stack depth but not to the actual worst-case stack depth.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* A nonatomic interrupt may only enable interrupts just before returning, at a point where it is using almost no stack memory.</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* Two interrupt handlers may never be runnable at the same time, for example because they service hardware devices that cannot be used concurrently.</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>In general, dealing with these issues is beyond the scope of tos-ramsize, which is intended to be simple.  Of course, you should feel free to provide patches that increase its precision, or parse its output and put the results together in new ways that permit more precise analysis.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>In general, dealing with these issues is beyond the scope of tos-ramsize, which is intended to be simple.  Of course, you should feel free to provide patches that increase its precision, or parse its output and put the results together in new ways that permit more precise analysis.</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2403&oldid=prevJohnRegehr: /* Memory Models */2009-04-21T04:13:54Z<p><span dir="auto"><span class="autocomment">Memory Models</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<col class="diff-content" />
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 04:13, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l28" >Line 28:</td>
<td colspan="2" class="diff-lineno">Line 28:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Every computer program has a ''memory model''.  For example, a typical UNIX process has a stack that grows down from high memory and a heap that grows up from low memory.  In practice, most UNIX programmers do not need to care about the details of this memory model because PCs have plenty of memory and in any case, the virtual memory system gives each process its own 32- or 64-bit address space.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Every computer program has a ''memory model''.  For example, a typical UNIX process has a stack that grows down from high memory and a heap that grows up from low memory.  In practice, most UNIX programmers do not need to care about the details of this memory model because PCs have plenty of memory and in any case, the virtual memory system gives each process its own 32- or 64-bit address space.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>In the most basic case (no heap, no threads) the memory model for a TinyOS application looks like this:</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>In the most basic case (no heap, no threads) the memory model for a TinyOS application <ins class="diffchange diffchange-inline">on a platform with 4 KB of RAM (mica2 or MicaZ) </ins>looks like this:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:summary.png]]</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:summary.png]]</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2402&oldid=prevJohnRegehr: /* Reducing Stack Memory Usage */2009-04-21T03:21:49Z<p><span dir="auto"><span class="autocomment">Reducing Stack Memory Usage</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class="diff-marker" />
<col class="diff-content" />
<col class="diff-marker" />
<col class="diff-content" />
<tr class="diff-title" lang="en">
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 03:21, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l238" >Line 238:</td>
<td colspan="2" class="diff-lineno">Line 238:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>As a programmer, there are a few easy things you can do to ensure that stack memory is not wasted:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>As a programmer, there are a few easy things you can do to ensure that stack memory is not wasted:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Make interrupt handlers atomic whenever possible.  This is good programming practice anyway.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Make interrupt handlers atomic whenever possible.  This is good programming practice anyway.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks make <del class="diffchange diffchange-inline">much more </del>efficient use of stack memory.  This is also good programming practice.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* Run as little code as possible in interrupt context.  Tasks make <ins class="diffchange diffchange-inline">very </ins>efficient use of stack memory.  This is also good programming practice.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid declaring large structs and arrays on the stack.  Of course, declaring them as global simply shifts the cost around; algorithmic changes may be required to save memory.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid excessively long call chains, but note that <tt>gcc</tt> is often very effective at making these go away through inlining.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* Understand the stack memory requirements of library code called by your application.  tos-ramsize can tell you about this if you crank up the verbosity.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* Understand the stack memory requirements of library code called by your application.  tos-ramsize can tell you about this if you crank up the verbosity<ins class="diffchange diffchange-inline">.  Or just run "objdump -d" on your elf file and look at the library code directly</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid creating an excessive number of threads, if using TOSThreads.  Unlike tasks, which share stack memory, threads have separate stacks.  Furthermore, each thread requires a large enough stack to support a full nesting of interrupts without overflowing onto the next thread's stack.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Avoid creating an excessive number of threads, if using TOSThreads.  Unlike tasks, which share stack memory, threads have separate stacks.  Furthermore, each thread requires a large enough stack to support a full nesting of interrupts without overflowing onto the next thread's stack.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2401&oldid=prevJohnRegehr: /* How Stack Analysis Works */2009-04-21T03:20:07Z<p><span dir="auto"><span class="autocomment">How Stack Analysis Works</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 03:20, 21 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l170" >Line 170:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= How Stack Analysis Works =</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= How Stack Analysis Works =</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Computing the worst-case stack memory used by a function is generally pretty simple: the pushes and pops along each path are added up.  A consequence is that each function and interrupt must have zero net stack effect at its return point; tos-ramsize will crash with an error if this appears to <del class="diffchange diffchange-inline">not </del>be the case.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Computing the worst-case stack memory used by a function is generally pretty simple: the pushes and pops along each path are added up.  A consequence is that each function and interrupt must have zero net stack effect at its return point; tos-ramsize will crash with an error if this appears <ins class="diffchange diffchange-inline">not </ins>to be the case.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The worst case stack depth of a collection of sequential code is equivalent to the longest path through the callgraph where edge weights are determined by per-function stack usage at callsites.</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The worst case stack depth of a collection of sequential code is equivalent to the longest path through the callgraph where edge weights are determined by per-function stack usage at callsites<ins class="diffchange diffchange-inline">, with additional edges added to the graph to account for stack memory usage of leaf functions</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>To put the sequential results together to create a global result, tos-ramsize assumes that the worst-case stack memory usage of an application occurs when:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>To put the sequential results together to create a global result, tos-ramsize assumes that the worst-case stack memory usage of an application occurs when:</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l181" >Line 181:</td>
<td colspan="2" class="diff-lineno">Line 181:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Thus, an application's worst-case stack depth is the stack usage of main() plus the sum of the stack memory used by all nonatomic interrupt handlers plus the maximum stack memory used by any atomic interrupt handler.  The assumption is that interrupt handlers may ''nest'' but that they may not ''reenter''.  These assumptions are discussed in more detail below.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Thus, an application's worst-case stack depth is the stack usage of main() plus the sum of the stack memory used by all nonatomic interrupt handlers plus the maximum stack memory used by any atomic interrupt handler.  The assumption is that interrupt handlers may ''nest'' but that they may not ''reenter''.  These assumptions are discussed in more detail below.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">There </del>are <del class="diffchange diffchange-inline">many subtleties of real code </del>that <del class="diffchange diffchange-inline">may cause </del>tos-ramsize <del class="diffchange diffchange-inline">to return a stack depth </del>that is too high:</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">One might argue that the worst-case stack depth has a low probability of being reached in practice.  In general, when multiple interrupt handlers </ins>are <ins class="diffchange diffchange-inline">involved, this is true.  The wrong way to reclaim some RAM is to optimistically assume </ins>that <ins class="diffchange diffchange-inline">the worst case will never happen.  The right ways to reclaim some RAM are discussed below.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">In some cases, </ins>tos-ramsize <ins class="diffchange diffchange-inline">is truly conservative, returning an upper bound </ins>that is too high<ins class="diffchange diffchange-inline">.  These include</ins>:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Some functions and/or interrupt handlers may be dead code.  They will contribute to estimated stack depth but not to the actual worst-case stack depth.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Some functions and/or interrupt handlers may be dead code.  They will contribute to estimated stack depth but not to the actual worst-case stack depth.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* A nonatomic interrupt may only enable interrupts just before returning, at a point where it is using almost no stack memory.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* A nonatomic interrupt may only enable interrupts just before returning, at a point where it is using almost no stack memory.</div></td></tr>
</table>JohnRegehrhttp://tinyos.stanford.edu/tinyos-wiki/index.php?title=Stack_Analysis&diff=2400&oldid=prevJohnRegehr: /* What is Stack Depth Analysis? */2009-04-20T22:13:51Z<p><span dir="auto"><span class="autocomment">What is Stack Depth Analysis?</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<col class="diff-content" />
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<tr class="diff-title" lang="en">
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 22:13, 20 April 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l3" >Line 3:</td>
<td colspan="2" class="diff-lineno">Line 3:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Calling a function or handling an interrupt causes ''stack memory'' to be allocated.  If the stack memory region -- the portion of a mote's RAM reserved for the stack -- is not large enough to hold the stack, a ''stack overflow'' occurs.  Stack overflow leads to corrupted RAM and subsequently to difficult, non-deterministic node failures.  These failures cannot be reproduced in TOSSIM, though they can be found in a CPU-level simulator such as Avrora or MSPsim.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Calling a function or handling an interrupt causes ''stack memory'' to be allocated.  If the stack memory region -- the portion of a mote's RAM reserved for the stack -- is not large enough to hold the stack, a ''stack overflow'' occurs.  Stack overflow leads to corrupted RAM and subsequently to difficult, non-deterministic node failures.  These failures cannot be reproduced in TOSSIM, though they can be found in a CPU-level simulator such as Avrora or MSPsim.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>We call an application ''stack safe'' if every stack memory region is large enough to contain the worst-case size of <del class="diffchange diffchange-inline">the </del>stack <del class="diffchange diffchange-inline">that it contains</del>.  A TinyOS application that does not use TOSThreads has a single stack and its size can be computed like this:</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>We call an application ''stack safe'' if every stack memory region is large enough to contain the worst-case size of <ins class="diffchange diffchange-inline">its </ins>stack.  A TinyOS application that does not use TOSThreads has a single stack and its size can be computed like this:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>::stack region size = RAM size - (data segment size + BSS segment size)</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>::stack region size = RAM size - (data segment size + BSS segment size)</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l12" >Line 12:</td>
<td colspan="2" class="diff-lineno">Line 12:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The ''worst observed stack depth'' is the largest stack size seen during testing.  Testing methods include observing the maximum extent of the stack using a simulator, periodically printing the value of the stack pointer from an interrupt handler, or filling the stack with known values and seeing how many get overwritten.  All testing-based techniques are unsafe in the sense that they can only provide a lower bound on the system's worst case stack memory usage.  The ''true worst case stack depth'' of a computer program is uncomputable; the best we can do is to try to narrow the gap between the lower and upper bounds.  Stack depth analysis -- the subject of this document -- is a technique for computing a safe upper bound on the worst-case stack memory requirements of an application.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The ''worst observed stack depth'' is the largest stack size seen during testing.  Testing methods include observing the maximum extent of the stack using a simulator, periodically printing the value of the stack pointer from an interrupt handler, or filling the stack with known values and seeing how many get overwritten.  All testing-based techniques are unsafe in the sense that they can only provide a lower bound on the system's worst case stack memory usage.  The ''true worst case stack depth'' of a computer program is uncomputable; the best we can do is to try to narrow the gap between the lower and upper bounds.  Stack depth analysis -- the subject of this document -- is a technique for computing a safe upper bound on the worst-case stack memory requirements of an application.</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">'''Note:''' Stack overflow -- as the term is used here -- is a distinct problem from buffer overflow (aka buffer overrun, stack-based buffer overflow).  The latter can be prevented using standard safe language techniques.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= Who Cares? =</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>= Who Cares? =</div></td></tr>
</table>JohnRegehr