SVC dump

An SVC dump provides a representation of the virtual storage for the system when an error occurs. Typically, a system component requests the dump from a recovery routine when an unexpected error occurs. However, an authorized program or the operator can also request an SVC dump when diagnostic dump data is needed to solve a problem.

An SVC dump comes in the following types, depending on how it was requested. Note that the type of dump requested determines its contents.
  • Asynchronous SVC dump (scheduled SVC dump):

    The system issues an instruction or the caller uses a combination of parameters on the SVC dump macro invocation. SVC dump captures all of the dump data into a set of data spaces then writes the dump data from the data spaces into a dump data set. The system is available for another SVC dump upon completion of the capture phase of the dump. In an asynchronous SVC dump, the summary dump data is captured first and can be considered more useful for diagnosis.

  • Synchronous SVC dump:

    The requester's SVC dump macro invocation issues an instruction to obtain the dump under the current task. The system returns control to the requester once the dump data has been captured into a set of data spaces. SVC dump processing then writes the dump data from the data spaces into a dump data set. The system is available for another SVC dump upon completion of the capture phase of the dump. In a synchronous SVC dump, the summary dump data is captured last.

Each SVC dump also contains a summary dump, if requested. Because dumps requested from disabled, locked, or SRB-mode routines cannot be handled by SVC dump immediately, system activity overwrites much useful diagnostic data. The summary dump supplies copies of selected data areas taken at the time of the request. Specifying a summary dump also provides a means of dumping many predefined data areas simply by specifying one option. Summary dump data is dumped using ASID(X'aaaa') SUMDUMP records and ASID(X'aaaa') DSPNAME(dddddddd) SUMDUMP records. The IPCS user has the option of causing storage dumped in these records also to be mapped as ASID(X'aaaa') or ASID(X'aaaa') DSPNAME(dddddddd) storage. Message BLS18160D is displayed during dump initialization when TSO prompting and IPCS confirmation options permit. If the TSO prompting and the IPCS confirmation options don't permit, the additional mapping is performed. Selective display of ASID(X'aaaa') SUMDUMP or ASID(X'aaaa') DSPNAME(dddddddd) SUMDUMP storage might be requested by referring to those address spaces.

This section includes information system programmers need to know about SVC dump and SVC dump processing:
See z/OS MVS Programming: Authorized Assembler Services Guide for information any programmer needs to know about programming the SDUMP or SDUMPX macros to obtain an SVC dump:
  • Deciding when to request an SVC dump
  • Understanding the types of SVC dumps that MVS™ produces
  • Designing an application program to handle a specific type of SVC dump
  • Identifying the data set to contain the dump
  • Defining the contents of the dump
  • Suppressing duplicate SVC dumps using dump analysis and elimination (DAE)