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version 1.19, 2017/06/26 17:18:57 version 1.20, 2018/09/05 14:27:12
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 Under some circumstances, you may lose the very first message of a panic,  Under some circumstances, you may lose the very first message of a panic,
 stating the reason for the panic.  stating the reason for the panic.
   
 <blockquote><pre>  <pre class="cmdbox">
 ddb> <b>show panic</b>  ddb> <b>show panic</b>
 0:      kernel: page fault trap, code=0  0:      kernel: page fault trap, code=0
 ddb>  ddb>
 </pre></blockquote>  </pre>
   
 <h3>Note for SMP systems</h3>  <h3>Note for SMP systems</h3>
   
 You should get a trace from each processor as part of your report:  You should get a trace from each processor as part of your report:
   
 <blockquote><pre>  <pre class="cmdbox">
 ddb{0}> <b>trace</b>  ddb{0}> <b>trace</b>
 pool_get(d05e7c20,0,dab19ef8,d0169414,80) at pool_get+0x226  pool_get(d05e7c20,0,dab19ef8,d0169414,80) at pool_get+0x226
 fxp_add_rfabuf(d0a62000,d3c12b00,dab19f10,dab19f10) at fxp_add_rfabuf+0xa5  fxp_add_rfabuf(d0a62000,d3c12b00,dab19f10,dab19f10) at fxp_add_rfabuf+0xa5
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 --- interrupt ---  --- interrupt ---
 idle_loop+0x21:  idle_loop+0x21:
 ddb{1}>  ddb{1}>
 </pre></blockquote>  </pre>
   
 Repeat the <tt>machine ddbcpu x</tt> followed by <tt>trace</tt> for each  Repeat the <tt>machine ddbcpu x</tt> followed by <tt>trace</tt> for each
 processor in your machine.  processor in your machine.
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 A typical kernel crash on OpenBSD might look like this:  A typical kernel crash on OpenBSD might look like this:
   
 <blockquote><pre>  <pre class="cmdbox">
 kernel: page fault trap, code=0  kernel: page fault trap, code=0
 Stopped at    <b>pf_route+0x263</b>:        mov     0x40(%edi),%edx  Stopped at    <b>pf_route+0x263</b>:        mov     0x40(%edi),%edx
 ddb>  ddb>
 </pre></blockquote>  </pre>
   
 This crash happened at offset <tt>0x263</tt> in the function <tt>pf_route</tt>.  This crash happened at offset <tt>0x263</tt> in the function <tt>pf_route</tt>.
   
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 The first command to run from the  The first command to run from the
 <a href="https://man.openbsd.org/ddb">ddb(4)</a> prompt is <tt>trace</tt>:  <a href="https://man.openbsd.org/ddb">ddb(4)</a> prompt is <tt>trace</tt>:
   
 <blockquote><pre>  <pre class="cmdbox">
 ddb> <b>trace</b>  ddb> <b>trace</b>
 <b>pf_route</b>(e28cb7e4,e28bc978,2,1fad,d0b8b120) at <b>pf_route+0x263</b>  <b>pf_route</b>(e28cb7e4,e28bc978,2,1fad,d0b8b120) at <b>pf_route+0x263</b>
 pf_test(2,1f4ad,e28cb7e4,b4c1) at pf_test+0x706  pf_test(2,1f4ad,e28cb7e4,b4c1) at pf_test+0x706
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 ipintr(10,10,e289f140,e289f140,e28cbd38) at ipintr+0x8d  ipintr(10,10,e289f140,e289f140,e28cbd38) at ipintr+0x8d
 Bad frame pointer: 0xe28cbcac  Bad frame pointer: 0xe28cbcac
 ddb>  ddb>
 </pre></blockquote>  </pre>
   
 This tells us what function calls lead to the crash.  This tells us what function calls lead to the crash.
   
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 Use <a href="https://man.openbsd.org/objdump">objdump(1)</a> to get the  Use <a href="https://man.openbsd.org/objdump">objdump(1)</a> to get the
 disassembly:  disassembly:
   
 <blockquote><pre>  <pre class="cmdbox">
 $ <b>cd /sys/arch/$(uname -m)/compile/GENERIC</b>  $ <b>cd /sys/arch/$(uname -m)/compile/GENERIC</b>
 $ <b>objdump -dlr obj/pf.o &gt;/tmp/pf.dis</b>  $ <b>objdump -dlr obj/pf.o &gt;/tmp/pf.dis</b>
 </pre></blockquote>  </pre>
   
 In the output, grep for the function name:  In the output, grep for the function name:
   
 <blockquote><pre>  <pre class="cmdbox">
 $ <b>grep "&lt;pf_route&gt;:" /tmp/pf.dis</b>  $ <b>grep "&lt;pf_route&gt;:" /tmp/pf.dis</b>
 0000<b>7d88</b> &lt;pf_route&gt;:  0000<b>7d88</b> &lt;pf_route&gt;:
 </pre></blockquote>  </pre>
   
 Take this first hex number <tt>7d88</tt> and add the offset <tt>0x263</tt> from  Take this first hex number <tt>7d88</tt> and add the offset <tt>0x263</tt> from
 the <tt>Stopped at</tt> line:  the <tt>Stopped at</tt> line:
   
 <blockquote><pre>  <pre class="cmdbox">
 $ <b>printf '%x\n' $((0x7d88 + 0x263))</b>  $ <b>printf '%x\n' $((0x7d88 + 0x263))</b>
 7feb  7feb
 </pre></blockquote>  </pre>
   
 Scroll down to the line <tt>7feb</tt>.  Scroll down to the line <tt>7feb</tt>.
 The assembler instruction should match the one quoted in the <tt>Stopped at</tt>  The assembler instruction should match the one quoted in the <tt>Stopped at</tt>
 line.  line.
 Then scroll up to the nearest C line number:  Then scroll up to the nearest C line number:
   
 <blockquote><pre>  <pre class="cmdbox">
 $ <b>more /tmp/pf.dis</b>  $ <b>more /tmp/pf.dis</b>
 /sys/net/pf.c:<b>3872</b>  /sys/net/pf.c:<b>3872</b>
     7fe7:       0f b7 43 02             movzwl 0x2(%ebx),%eax      7fe7:       0f b7 43 02             movzwl 0x2(%ebx),%eax
     <b>7feb</b>:       8b 57 40                <b>mov    0x40(%edi),%edx</b>      <b>7feb</b>:       8b 57 40                <b>mov    0x40(%edi),%edx</b>
     7fee:       39 d0                   cmp    %edx,%eax      7fee:       39 d0                   cmp    %edx,%eax
     7ff0:       0f 87 92 00 00 00       ja     8088 &lt;pf_route+0x300&gt;      7ff0:       0f 87 92 00 00 00       ja     8088 &lt;pf_route+0x300&gt;
 </pre></blockquote>  </pre>
   
 So, it's precisely line <tt>3872</tt> of <tt>pf.c</tt> that crashes:  So, it's precisely line <tt>3872</tt> of <tt>pf.c</tt> that crashes:
   
 <blockquote><pre>  <pre class="cmdbox">
 $ <b>nl -ba /sys/net/pf.c | sed -n 3872p</b>  $ <b>nl -ba /sys/net/pf.c | sed -n 3872p</b>
   3872          if ((u_int16_t)ip-&gt;ip_len &lt;= ifp-&gt;if_mtu) {    3872          if ((u_int16_t)ip-&gt;ip_len &lt;= ifp-&gt;if_mtu) {
 </pre></blockquote>  </pre>
   
 The kernel that produced the crash output and the object file for objdump must  The kernel that produced the crash output and the object file for objdump must
 be compiled from the exact same source file, otherwise the offsets won't match.  be compiled from the exact same source file, otherwise the offsets won't match.
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