HP OpenVMS Systems Documentation

HP OpenVMS Calling Standard

Given an invocation context block and general register index such that 0 <= index < 128, copy the register value to gr_copy, for example, index 4 fetches the invocation context block IREG[4] value, which represents the contents of R4 for the context.

If the register represented by index has its corresponding NaT bit set, the read succeeds and the return status is set to 3. If the register represented by index lies beyond the allocated general registers, the read fails and gr_copy is unchanged. That is, the highest allowed index is 32 + ICB.CFM.SOF - 1.

LIB$I64_GET_GR fails if the index represents a scratch register whose contents have not been realized.

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Given an invocation context block, a general register index such that 1 <= index < 128, and a quadword value gr_copy, writes the corresponding invocation context block general register, clears the corresponding NaT bit and uses LIB$I64_PUT_INVO_REGISTERS to write to the actual context. The invocation context block remains unchanged if the routine fails.

LIB$I64_SET_GR fails if LIB$I64_PUT_INVO_REGISTERS fails.

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Given an invocation context block and a quadword PC value in pc_copy, write the pc_copy value to the invocation context block PC and then use LIB$I64_PUT_INVO_REGISTERS to write to the actual context. The invocation context block remains unchanged if the routine fails.

LIB$I64_SET_PC fails if LIB$I64_PUT_INVO_REGISTERS fails.

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Given a pc_value, find the address of the unwind information block language-specific data area (LSDA), and write it to unwind_lsda_p. If not present, then write 0 to unwind_lsda_p.

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Given a pc_value, find the address of the unwind information block operating system-specific data area, if present, and write it to unwind_ossd_p. If not present, then write 0 to unwind_ossd_p.

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Given a pc_value, find the function value (address of the procedure descriptor) for the condition handler, if present, and write it to handler_fv. If not present, then write 0 to handler_fv.

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Used to determine whether a given PC value represents an exception dispatch frame.

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Used to determine whether a given PC value represents an AST dispatch frame.

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Advanced users can override the way the call stack is traced by providing custom callback routines. These routines can be used to perform the following functions:

• Perform a call trace on a process other than the current process.
• Override the heap storage mechanism used to allocate memory used during the analysis of unwind descriptors.

The user override callback mechanism provides a user ident value that is passed to each callback routine. The user ident value is stored in the LIBICB$IH_UO_IDENT field of the invocation context block.

The routines described in this section must be provided to override the call stack walk.

Place a function pointer for this routine in the LIBICB$PH_UO_GETUEINFO field of the invocation context block.

This routine should mimic SYS$GET_UNWIND_ENTRY_INFO for the target process. See Section A.6 for detailed argument descriptions and return status, with the following notes:

The name argument is not used, and can be ignored. If a read memory callback has been specified, the contents of LIBICB$PH_UO_READ_MEM are passed as a fourth argument, and the contents of LIBICB$PH_UO_IDENT are passed as a fifth argument, otherwise the routine is called with three arguments.

4.8.5.2 The Get Initial Context Routine

Place a function pointer for this routine in the LIBICB$PH_UO_GETCONTEXT field of the invocation context block.

The get initial context routine is used to seed the invocation context block from the target process. This routine should initialize the invocation context block structure with the preserved general, floating, branch, and predicate registers, as well as Application Registers such as AR.RSC, AR.BSP, and AR.PFS from the target process. This routine should set the valid bits corresponding to the saved registers in the VALID fields. This routine must store the original spill address corresponding to R0 in the ORIGINAL_SPILL_ADDR field. This callback routine is used by LIB$I64_GET_CURR_INVO_CONTEXT and should be followed by at least one call to LIB$I64_GET_PREV_INVO_CONTEXT to generate a working context.

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Place a function pointer for this routine in the LIBICB$PH_UO_READ_MEM field of the invocation context block.

The read memory routine is used to transfer data from the target process.

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Place a function pointer for this routine in the LIBICB$PH_UO_WRITE_MEM field of the invocation context block.

The write memory routine is used to transfer data to the target process. It is used by LIB$I64_PUT_INVO_REGISTERS for a register that has been saved in memory.

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