What happens when a segment descriptor is loaded in real or Virtual 8086 mode? \ VOGONS

What happens when a segment descriptor is loaded in real or Virtual 8086 mode?

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First post, by superfury

Posted on 2016-09-13, 07:05

superfury Offline

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I understand that the base gets updated with the segment's new value shifted left by 4(multiplied by 16). Segment CS also gets loaded with it's rights byte (0x9D?).

Does anything else get loaded in real/virtual 8086 mode? What about the other segment descriptor fields, as wel as other segment registers than CS? Or do they not get modified (except the base field)?

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Reply 1 of 1, by peterferrie

Posted on 2016-09-13, 19:04

peterferrie Offline

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CS isn't updated unless accessed implicitly (int/jmp/call/ret), so you can continue to access memory as though you were in real mode with cs: override, even while DS/ES carry selectors.
When the descriptor is loaded, base, limit, and rights are loaded, too, but only for that register.

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