Re: Doubts about Segmentation
- From: robertwessel2@xxxxxxxxx
- Date: 28 Apr 2006 22:33:43 -0700
Dirk Wolfgang Glomp wrote:
Well, not really. MZ had no provision for such, but a number of folks
created overlay linkers which allowed the overlays to be attached to
the end of the MZ (which was what the OS loaded), but they were never
really part of it. The overlay linker would add code to your program
to load and manage the overlays, it was never an OS function.
RBIL->Inter61b.zip->Interrup.g
INT 21 - DOS 2+ - "EXEC" - LOAD AND/OR EXECUTE PROGRAM
AH = 4Bh
AL = type of load
03h load overlay
Offset Size Description (Table 01591)
00h WORD segment at which to load overlay
02h WORD relocation factor to apply to overlay if in .EXE format
...but i never test it.
That MS-DOS function is not really any sort of overlay manager as one
would normally understand the term. 0x4b03 loads an ordinary
executable (COM or MZ) into memory, at a location you specify, and with
a relocation factor you specify (usually the two are the same), but
does not create any sort of execution environment (PSP, environment,
etc. for it, nor does it start executing it. It just loads the
executable into memory, and returns control to your program (which
would then presumably do something with the loaded program).
In any event, this still doesn't imply that there's any sort of overlay
structure defined for MZ files, since the function just loads an entire
ordinary MZ, not some part of a MZ. It would certainly be possible to
use that for the basis of an overlay manager (and several folks did),
although it does require that each overlay live in a separate file
.
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- Re: Doubts about Segmentation
- From: Dirk Wolfgang Glomp
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