VMS Help MACRO, VAX MACRO Assembler, Instructions, CALLG  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Purpose:        Call with general argument list - invoke a procedure
                    with actual arguments from anywhere in memory
    Format:         opcode arglist.ab,dst.ab
    Operation:      {align stack}; {create stack frame}; {set arithmetic
                    trap enables}; {set new values of AP, FP, PC}
    C. Codes:       N = 0, Z = 0, V = 0, C = 0
    Exceptions:     Reserved operand
    Opcode:         FA    CALLG    Call proc., general arglist
    Description:    SP is saved in a temporary (tmp) and then bits 1:0
                    of SP are cleared so the stack is longword aligned.
                    The procedure entry mask (pointed to by dst) is
                    scanned from bit 11 to bit 0 and the contents of the
                    registers whose numbers correspond to set bits in
                    the mask are pushed on the stack as longwords. Next
                    AP, FP and the current PC are pushed onto the stack
                    as longwords. The condition codes are cleared. A
                    longword containing the saved two low bits of SP in
                    bits 31:30 (tmp), 0 in bits 29:28, the low 12 bits
                    of the entry mask in bits 27:16 and the PSW in bits
                    15:0 with T cleared is pushed on the stack. A
                    longword 0 is pushed on the stack (for the condition
                    handler). FP is replaced by SP, AP is replaced by
                    arglist. The trap enables in PSW are set to a known
                    state. Integer and decimal overflow are set
                    according to bits 14 and 15 of the entry mask
                    respectively. The floating underflow bit is cleared
                    and the T-bit is unaffected. PC is replaced by dst +
                    2, skipping the entry mask and transferring control
                    to the byte beyond the mask.