Finding the stack storage blocks

You might need to locate all stack storage blocks (SKBs) that are associated with the failing agent in any SVC dump that is issued by Db2, including the SKBs that are associated with all synchronously-created execution blocks (EBs) related to the failing agent.

About this task

Use this information at the request of IBM® Support staff when you analyze the unformatted section of an SVC dump. Stack storage usually appears toward the end of the formatted section of the dump.

The following figure displays how to locate the stack storage for the failing agent.

To find the stack storage blocks:

1. Locate the EBSKB field in the failing EB. This field points to the primary SKB for that EB.
2. Determine the address space in which this primary SKB resides.
   • Use the EBPASCE field in the EB to obtain the address of the ASCE.
   • Find the address space in the ASCEASID field of the ASCE. This address space is the address space of the SKB.

   In the SKB, two fields contain important addresses:

   SKBNEXTS

   This field contains the address of the next SKB within this stack. Multiple SKBs can be associated with this primary SKB. Each of these stack segments is considered part of this primary SKB.

   When SKBNEXTS equals zero, all of the stack segments for that primary SKB are located.

   SKBOSKB

   This field contains the address of the previous primary SKB, which was in a previous address space (identified in the field named SKBPASCE). To determine which address space the previous primary SKB was in, see the SKBPASCE field in this SKB; this field points to the ASCE. The field in the ASCE named ASCEASID identifies the address space that contains the SKB.

   Although this SKB is a different primary SKB than the one pointed to directly by the EB, it is still associated with that EB.

   There can be a chain of primary SKBs associated with one EB. For each primary SKB in that chain, there can be a chain of stack segments (SKBs). When SKBOSKB equals zero, the end of the chain of primary SKBs associated with that EB is located.

3. After you locate all the stack storage for the failing EB, locate the stack storage for all other EBs related to the failing agent.

   Review the EBCHA field in the failing EB. This field contains the address of another related EB (and likewise, that EB's EBCHA field points to another related EB). These other EBs also have chains of primary SKBs (and possibly of stack segments), as did the failing EB. When you locate an EB whose EBCHA field equals zero, all of the stack storage for all the EBs related to the failing agent is located.