Finding the right address

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While in the Kernel Debugger, there is a structure that can be searched that gives the address of the trace buffer and first device handle. For DIAGEX, this structure is diag_cntl. For PDIAGEX, it is pdiag_cntl. Use the map command to get the address of the structure.

Note: The following examples are based on a particular debugger. The concepts shown can be applied using the debugger available to you.

For instance, for PDIAGEX:


  1. 
>0> map pdiag_cntl
pdiag_cntl:0x0123F220, type:CSECT Definition
  2. Use that address and display 100 words: 
    
>0> d 123F220 100
0123F220   FFFFFFFF FFFFFFFF 05C8A400 00000764   |...............d|
0123F230   64677874 72616365 544F5021 21212100   |dgxtraceTOP!!!!.|
0123F240   72775F61 00000004 00000000 00000000   |rw_a............|
0123F250   67697042 00000018 00000004 2FF3B270   |gipB......../..p|
0123F260   67697064 000000C0 00000000 3D7FF018   |gipd........=...|
0123F270   67697045 00000000 3D7FF018 00000000   |gipE....=.......|
0123F280   72775F62 00000001 00000001 00000001   |rw_b............|
0123F290   72775F45 00000000 00000000 00000000   |rw_E............|
0123F2A0   52656445 00000000 20001111 00000000   |RedE.... .......|
0123F2B0   57727442 05C8A200 00000004 00000014   |WrtB............|
0123F2C0   5772742B 14000000 00000001 00000001   |Wrt+............|
0123F2D0   5772742B 00000001 0000007B 00000000   |Wrt+.......{....|
0123F2E0   72775F42 05C8A200 00000001 00000001   |rw_B............|
0123F2F0   72775F2B 00000004 00000014 00000001   |rw_+............|
0123F300   72775F2B 0000007B 14000000 00000001   |rw_+...{........|
0123F310   66685F42 05C8A200 05C8A200 00000000   |fh_B............|
    • The first and second words, FFFFFFFF, are locks. Ignore them.
    • The third word (in bold) is a pointer to the linked list of device handles.
    • The fourth word is the start of the internal trace table.
    • dgxtraceTOP! defines the TOP of the trace table.
    • dgxtraceBOT! defines the end of the trace table.
  3. The current pointer can be found by searching from this point for dgxtraceCUR!: 
    
>0> find dgxtraceCUR 123F220
01240FC0   64677874 72616365 43555221 21212121   |dgxtraceCUR!!!!!|

    Work backwards from this point to see exactly what events have taken place to this point.

  4. As far as the device handles are concerned, display 100 words to see the data associated with the device at that address (the third word from 2.b above): 
    
>0> d 05C8A400 100
05C8A400   00000000 012438B8 00040040 0000000D   |.....$8....@....|
05C8A410   00000003 000000C0 0000002C 00000000   |...........,....|
05C8A420   011759FC 05F1D000 00000000 60054335   |..Y.........`.C5|
05C8A430   00000000 00000000 00000070 000000C0   70 is slot#, C0 is bus id#
05C8A440   00000004 007FF800 00000100 00000000    4 is bus type 7ff800 is io
05C8A450   00000100 00000000 00000000 00000000       address of the bus

    The 8th word is a pointer to the next device in the linked list. In this case the 8th word is 00000000, indicating this is the only device.