Windows Calling Conventions

This manual presents the syntax of most functions in C-language notation. All such functions are assumed to be declared as FAR PASCAL functions, and Windows will call these functions as such. In general, exported functions in a device driver must execute the standard Windows prolog on entry and epilog on exit.

The following list highlights the calling conventions:

• Set the DS register to the selector of the driver's automatic data segment.
• Save and restore the following registers if used: SS, SP, BP, SI, DI, and DS.
• Clear the direction flag if it has been set or modified.
• Place 16-bit return values in the AX register; 32-bit values in the DX:AX register pair.
• Execute a FAR return.

Windows pushes all parameters on the stack in a left to right order (the last parameter shown in the function syntax is closest to the stack pointer). Windows also passes pointer parameters as 32-bit quantities, pushing the selector first then the offset. This allows exported functions to use the lds or les instructions to retrieve pointers from the stack.