4.104.114.84.95
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1 | # |
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2 | # $Id$ |
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3 | # |
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4 | |
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5 | This directory contains a stack bounds checker. It provides two |
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6 | primary features: |
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7 | |
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8 | + check for stack overflow at each context switch |
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9 | + provides an educated guess at each task's stack usage |
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10 | |
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11 | The stack overflow check at context switch works by looking for |
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12 | a 16 byte pattern at the logical end of the stack to be corrupted. |
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13 | The "guesser" assumes that the entire stack was prefilled with a known |
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14 | pattern and assumes that the pattern is still in place if the memory |
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15 | has not been used as a stack. |
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16 | |
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17 | Both of these can be fooled by pushing large holes onto the stack |
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18 | and not writing to them... or (much more unlikely) writing the |
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19 | magic patterns into memory. |
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20 | |
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21 | This code has not been extensively tested. It is provided as a tool |
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22 | for RTEMS users to catch the most common mistake in multitasking |
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23 | systems ... too little stack space. Suggestions and comments are appreciated. |
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24 | |
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25 | NOTES: |
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26 | |
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27 | 1. Stack usage information is questionable on CPUs which push |
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28 | large holes on stack. |
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29 | |
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30 | 2. The stack checker has a tendency to generate a fault when |
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31 | trying to print the helpful diagnostic message. If it comes |
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32 | out, congratulations. If not, then the variable Stack_check_Blown_task |
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33 | contains a pointer to the TCB of the offending task. This |
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34 | is usually enough to go on. |
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35 | |
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36 | FUTURE: |
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37 | |
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38 | 1. Determine how/if gcc will generate stack probe calls and support that. |
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39 | |
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40 | 2. Get accurate stack usage numbers on i960.. it pushes very large |
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41 | holes on the stack. |
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