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matefkr



Joined: 02 Sep 2007
Posts: 1291
Location: Ukraine, Beregovo
matefkr
hi. i have some question about memory addressing:
-in protected mode, is the segment base address (in descriptors) only for protection (to sign the begining of a segment), or that used to calculate the memory ( i mean that the physical address will be the offset ([ebx] for example) plus the segment base address).

-how descriptor cashes used in real mode (on new processors)? i mean, that are they only for protection, to controll the operand and address size and such, or not ( i guess yes)?


Last edited by matefkr on 23 Sep 2007, 18:14; edited 1 time in total
Post 23 Sep 2007, 17:41
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
segment base address is also used to count final address. so final address is segment base address + offset.

segment limit still works under real mode, segment base is ignored, 32/16bit code works (but interrupt still push only 16bit IP on stack), don't know about others.
Post 23 Sep 2007, 17:58
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matefkr



Joined: 02 Sep 2007
Posts: 1291
Location: Ukraine, Beregovo
matefkr
ok thank you!
Post 23 Sep 2007, 18:09
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matefkr



Joined: 02 Sep 2007
Posts: 1291
Location: Ukraine, Beregovo
matefkr
Just one more thing:

[quote="vid"](but interrupt still push only 16bit IP on stack), don't know about others.[/quote]

Is that mean, that even hardware interrupts (i guess)? so if i hit a key on the keyboard, it will push only 16 bit offset when interrupt?
Post 05 Oct 2007, 07:52
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
yes... no way to place code above 1MB
Post 05 Oct 2007, 10:29
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matefkr



Joined: 02 Sep 2007
Posts: 1291
Location: Ukraine, Beregovo
matefkr
Another questions:
-can i use address and operand size prefix in real mode?
-You mean no way to place code above 1mb if i want interrupts to work correctly or you meant that no way to hold the cs descriptor cache (will it updated anyway?).
Post 13 Oct 2007, 13:13
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
- yes, use can use prefixes.
- you can't. Not because cached CS - that stays unchanged. It is because offset pushed is 16 bit even if code is 32bit.
Post 14 Oct 2007, 17:36
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matefkr



Joined: 02 Sep 2007
Posts: 1291
Location: Ukraine, Beregovo
matefkr
thanks!
Post 15 Oct 2007, 17:41
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