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Using SLIP TRACEs
Sometimes it is desirable to get information about the contents of registers
or data areas for a program that is not behaving as expected without
altering or interrupting the operation of that program. The SLIP subcommand
of OPER can be used to collect this information. The following SLIP command:
<![CDATA[
SLIP SET,IF,ID=xxxx,A=TRACE,TRDATA=(STD,REGS),J=jobname,PVTMOD=(pgm,start,end),END
]]>
will trace activity in the specified program (pgm) between offsets "start" and "end"
for job, user or started task "jobname". An entry is to be created for each instruction
fetch (IF) which matches the specified criteria. You want to be as specific as possible
to avoid introducing unnecessary overhead into your system. For each matching event,
an entry will be creating containing a standard header and register contents.
The SLIP command supports other selection criteria for specifying which events
should be monitored and what data should be collected. For example, you can specify
that the contents of an area pointed to by the contents of a specified register be
captured for each matching event. Refer to the "MVS System Commands" publication
or the "Service Aids" publication for more details.
To collect this information, you need to have GTF running specifying a parm member
similar to the following:
<![CDATA[
TRACE=SLIP
]]>
GTF is started using an operator command similar to the following:
<![CDATA[
S GTF.GTF,MEMBER=parm,DSN=tracedsn
]]>
GTF will at this point normally issue a message like:
<![CDATA[
xx AHL125A RESPECIFY TRACE OPTIONS OR REPLY U
]]>
Respond with the operator command R xx,U to continue. Once the activity that you
wanted to monitor has completed, enter P GTF to stop GTF. Enter the command
<![CDATA[
SLIP DEL,ID=xxxx
]]>
to remove your slip.The procedure used to start GTF may vary depending on your
installation's procedures.
You can check out the contents of your trace using IPCS. You can either use
the GTFTRACE command of IPCS or use the IPCS panels for formatting trace
output, using the dataset name specified to GTF earlier as input.
For more information, refer to the "Service Aids" publication associated with
your release of MVS.
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