ILC between XPLINK and COBOL

The only way a COBOL routine can call an XPLINK-compiled routine is if the caller is compiled with the Enterprise COBOL for z/OS® or COBOL for OS/390® & VM compiler with the DLL compiler option, and the target of the call is in a separate DLL, or vice versa.

COBOL Dynamic Call to XPLINK is not supported.

Since XPLINK compatibility is only provided to Language Environment-conforming languages, OS/VS COBOL programs and VS COBOL II programs are not supported in an XPLINK(ON) environment.

The COBOL reusable environment support (the RTEREUS runtime option or the callable interfaces ILBOSTP0 and IGZERRE) cannot be used in an XPLINK(ON) environment.

COBOL ILC with an XPLINK function in a separate DLL can employ either of two parameter passing techniques:

The "pragmaless" style, where the COBOL programmer explicitly specifies syntax indicating that arguments are to be passed BY VALUE, and uses RETURNING syntax to access C function results.
RETURNING values and BY VALUE arguments are implemented using pre-XPLINK C linkage conventions, and are designed to enable pragma-less ILC with C or with C++ using EXTERN C. This technique also works with XPLINK. In this case, the glue code will load the necessary XPLINK parameter registers when called from a COBOL function, or store them into the argument area when calling a COBOL function.
The #pragma linkage(..., COBOL) style, where the COBOL programmer specifies normal BY REFERENCE argument conventions, the C functions specify normal C by-value conventions, and the XL C/C++ compiler introduces code to accommodate both.
An XPLINK program can identify a called function as using a COBOL-style parameter list (R1 => list of addresses, with the High Order Bit (HOB) of the last parameter turned on):
```
#pragma linkage(called_rtn,COBOL)
```
In this case the XPLINK compiler generates a list of addresses to the actual parameters. The only difference is that XPLINK loads up to the first three of these addresses into registers 1, 2, and 3. When the glue code receives control from the XPLINK caller to swap the stack before giving control to the called COBOL function, it also creates a complete by-reference parameter list and set register 1 with the address of this parameter list.
An XPLINK function can also specify that it receives COBOL-style parameters as input:
```
#pragma linkage(this_rtn,COBOL)
```
Processing via glue code is similar – when the XPLINK function receives control, the first three parameter addresses have been loaded into the parameter registers.