1 | # |
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2 | # $Id$ |
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3 | # |
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4 | |
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5 | Introduction |
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6 | ============ |
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7 | |
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8 | This directory contains a stack bounds checker. It provides two |
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9 | primary features: |
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10 | |
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11 | + check for stack overflow at each context switch |
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12 | + provides an educated guess at each task's stack usage |
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13 | |
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14 | Enabling |
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15 | ======== |
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16 | |
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17 | Add the stack checker extension to the initial user extension set. |
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18 | If using confdefs.h to build your configuration table, this is |
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19 | as simple as adding -DSTACK_CHECK_ON to the gcc command line which |
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20 | compiles the file defining the configuration table. In the RTEMS |
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21 | test suites and samples, this is always init.c |
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22 | |
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23 | Background |
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24 | ========== |
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25 | |
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26 | The stack overflow check at context switch works by looking for |
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27 | a 16 byte pattern at the logical end of the stack to be corrupted. |
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28 | The "guesser" assumes that the entire stack was prefilled with a known |
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29 | pattern and assumes that the pattern is still in place if the memory |
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30 | has not been used as a stack. |
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31 | |
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32 | Both of these can be fooled by pushing large holes onto the stack |
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33 | and not writing to them... or (much more unlikely) writing the |
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34 | magic patterns into memory. |
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35 | |
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36 | This code has not been extensively tested. It is provided as a tool |
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37 | for RTEMS users to catch the most common mistake in multitasking |
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38 | systems ... too little stack space. Suggestions and comments are appreciated. |
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39 | |
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40 | NOTES: |
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41 | |
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42 | 1. Stack usage information is questionable on CPUs which push |
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43 | large holes on stack. |
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44 | |
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45 | 2. The stack checker has a tendency to generate a fault when |
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46 | trying to print the helpful diagnostic message. If it comes |
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47 | out, congratulations. If not, then the variable Stack_check_Blown_task |
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48 | contains a pointer to the TCB of the offending task. This |
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49 | is usually enough to go on. |
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50 | |
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51 | FUTURE: |
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52 | |
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53 | 1. Determine how/if gcc will generate stack probe calls and support that. |
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