Transferring data along with code for program overlays

A method for generating program overlays from a sequence of program code, the program code having common code and code to be overlaid, each overlay having a set of code and related data contained therein, the overlays being transferred via an overlay manager from a storage area to a receiving area for processing, the method comprising the steps of:

• (a) reserving a memory segment in the receiving area to hold overlaid code and data;
• (b) breaking the sequence of code to be overlaid into a set of segments, wherein each segment contains a certain amount of related code for processing, and each segment is sized to fit in the reserved memory segment;
• (c) creating stubs for each code segment, whereby the stubs represent entry points for functions within each code segment;
• (d) linking the common code along with the stubs for each code segment;
• (e) importing symbols from the common code and linking the next individual code segment in the set of segments to produce an image;
• (f) extracting overlay code and data from the image produced in step (e);
• (g) checking if more segments exist in the set, if yes, then return to step (e), else proceed to step (h);
• and
• (h) concatenating the overlays into a file which can be referenced by the overlay manager.

A method for generating program overlays from a sequence of program code, the program code having common code area and overlay code area, each overlay having a set of code and related data contained therein, the overlays being transferred via an overlay manager from a storage area to a receiving area for processing, the method comprising the steps of:

• (a) analyzing the overlay code area and determining the function entry points for each overlay;
• (b) creating an overlay control file for each overlay, whereby the overlay control file describes each pair of code and data associated with each overlay;
• (c) generating a wrapper file from the overlay control file;
• (d) creating a linker command file for the common area;
• (e) creating a linker command file for the overlay area;
• (f) performing an initialization for the overlay;
• (g) creating a common image for the code and data;
• (h) producing overlay sections from the image;
• (i) producing an overlay sections file;
• and
• (j) producing a load command file, whereby the command file will load the overlay sections file into the appropriate receiving area.