Jonathan de Boyne Pollard wrote in a message to John Lisek:

 JdBP>   The -zw, -zW, and -zWs switches control the generation of
 JdBP> the prologues   necessary on DOS+Windows for "instance
 JdBP> thunking" (i.e. all of the messy   mechanics of
 JdBP> MakeProcInstance).  In 16-bit OS/2 there is no such thing. 

 JdBP>   In 16-bit OS/2 all that is required of a function that can
 JdBP> be called   from outside the EXE or DLL containing it is
 JdBP> that it ensure that it   loads the DGROUP for the EXE/DLL
 JdBP> into the DS register on entry.  There   are no instance
 JdBP> thunks, no MakeProcInstance, and the much longer   function
 JdBP> prologues used by DOS+Windows are not required.

This isn't quite true of Ring 0 DLLs, such as FSDs.  In such special cases,
you do have to worry about whether DS is pegged or floating, and so on.
 
-- Mike


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