8.2.3 Overlay data tables

armlink provides various symbols that point to a piece of read-only data, mostly arrays. This data describes the collection of overlays and overlay regions in the image.

The symbols are:

Region$$Table$$AutoOverlay
This symbol points to an array containing two 32-bit pointers per overlay region. For each region, the two pointers give the start address and end address of the overlay region. The start address is the first byte in the region. The end address is the first byte beyond the end of the region. The overlay manager can use this symbol to identify when the return address of a calling function is in an overlay region. In this case, a return thunk might be required.

Note:

The regions are always sorted in ascending order of start address.
Region$$Count$$AutoOverlay
This symbol points to a single 16-bit integer (an unsigned short) giving the total number of overlay regions. That is, the number of entries in the arrays Region$$Table$$AutoOverlay and CurrLoad$$Table$$AutoOverlay.
Overlay$$Map$$AutoOverlay
This symbol points to an array containing a 16-bit integer (an unsigned short) per overlay. For each overlay, this table indicates which overlay region the overlay expects to be loaded into to run correctly.
Size$$Table$$AutoOverlay
This symbol points to an array containing a 32-bit word per overlay. For each overlay, this table gives the exact size of the data for the overlay. This size might be less than the size of its containing overlay region, because overlays typically do not fill their regions exactly.

In addition to the read-only tables, armlink also provides one piece of read/write memory:

CurrLoad$$Table$$AutoOverlay
This symbol points to an array containing a 16-bit integer (an unsigned short) for each overlay region. The array is intended for the overlay manager to store the identifier of the currently loaded overlay in each region. The overlay manager can then avoid reloading an already-loaded overlay.

All these data tables are optional. If your code does not refer to any particular table, then it is omitted from the image.

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