Upward-growing (non-XPLINK) stack frame section

The stack frame, also called dynamic save area (DSA), for each active routine is listed in the full dump.

A stack frame chain is associated with each thread in the runtime environment and is acquired every time a separately compiled procedure or block is entered. A stack frame is also allocated for each call to a Language Environment service. All stack frames are back-chained with a stopping stack frame (also called a dummy DSA) as the first stack frame on the stack. Register 13 addresses the recently active stack frame or a standard register save area (RSA). The standard save area back chain must be initialized, and it holds the address of the previous save area. Not all Language Environment-conforming compilers set the forward chain; thus, it cannot be guaranteed in all instances. Calling routines establish the member-defined fields.

When a routine makes a call, registers 0–15 contain the following values:

R1 is a pointer to parameter list or 0 if no parameter list passed.
R0, R2–R11 is unreferenced by Language Environment. Caller’s values are passed transparently.
R12 is the pointer to the CAA if entry to an external routine.
R13 is the pointer to caller’s stack frame.
R14 is the return address.
R15 is the address of the called entry point.

With an optimization level other than 0, C/C++ routines save only the registers used during the running of the current routine. Non-Language Environment RSAs can be in the save area chain. The length of the save area and the saved register contents do not always conform to Language Environment conventions. For a detailed description of stack frames Language Environment storage management, see z/OS Language Environment Programming Guide. Figure 1 shows the format of the upward-growing stack frame.

Note: The Member-defined fields are reserved for the specific higher level language.

Figure 1. Upward-growing (non-XPLINK) stack frame format