This chapter discusses the calling conventions used by PL/I for Windows:
The OPTLINK linkage convention (see OPTLINK linkage for details) is also supported by VisualAge for C++ (OS/2 and Windows) and is the fastest method of calling PL/I procedures, C functions, or assembler routines. OPTLINK is not, however, standard for all Windows applications.
On Windows, specifying SYSTEM linkage is synonymous with STDCALL linkage and is implemented the same as STDCALL. The compiler, however, considers the names SYSTEM and STDCALL to be distinct and complains if you mix them. The STDCALL linking convention is described in STDCALL linkage (Windows only).
You can specify the calling convention for all functions within a program using the LINKAGE suboption of the DEFAULT compile-time option. You can also use the LINKAGE option of the OPTIONS attribute to specify the linkage for individual functions.