gtpg2m0a | General Macros |
The executive macros are divided into two general groups: control program macros and application macros. All executive macro names consist of 5 alpha characters. The last letter of the macro name distinguishes between control program macros (C) and application macros (A). A few application macro names violate this general rule.
Control program macros are used to provide a linkage to the system service routines. Generally, this implies the generation of a supervisor call (SVC) instruction and parameters that specify the desired service. The macro decoder routine of the control program, in the case of an SVC, selects the appropriate control program routine to perform the service. In some instances, the linkage is done with branch and link instructions to improve the performance of executing frequently used functions.
Application macros can generate a sequence of machine instructions. A control program macro generally generates only enough code to link to the desired service routine. An application macro can generate data or indirectly generate linkage code through the use of a control program macro.
If an application macro definition uses a control program macro, a linkage will, of course, be generated for the system service routines. The distinction is:
Some of the application macros are specifically designed for the offline programs. Another subset is specifically designed for building structured programs.
The format of the executive (control program and application program) macro instruction used in source code is as follows:
There are 3 major macro instruction operand (parameter) formats.