We recommend that you write your assembler subprograms to comply with the standard COBOL calling convention (bits 0 and 1 set to 0, the default). The assembler subprogram can consist of multiple code and data segments.
Assembler subprograms must be dynamically linked.
The registers used, assuming the standard call convention, are:
| Register | Usage |
|---|---|
| ESP | holds the return address, followed by parameters which have been pushed in right to left order |
| EBP, EBX, ESI, EDI | must be preserved by the called program |
| EAX | holds the return-code for four byte data items |
| EDX:EAX register pair | holds the return-code for an eight byte structure |
For an example, see Example of Calling an Assembler Subprogram.