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FS#230 - x86 segmentation support
User who did this: - Ali Saidi (saidi)

Attached to Project - M5 Bugs
Summary - x86 segmentation support
Task Type - Minor Enhancement
Category - ISA Support
Status - New
Assigned To - Gabe Black
Operating System - All
Severity - Low
Priority - Normal
Reported Version - 1.1
Due in Version - 2.1
Due Date - Undecided
Percent Complete - 50%
Details - Added needed support for segmentation to support x86.

First, it needs to be determined how much segmentation support we
really need. If the processor is in long mode which is activated by
the operating system, processes can operate in one of two sub modes.
In the 64 bit submode, segmentation is ignored except for the
attributes of the code segment (which determine if you're in 64 bit
mode, among a few other things) and the bases and limits of the fs and
gs segments. In the compatibility submode, processes see the
segmentation semantics of the legacy protected mode, ie all of the
user level features.

Second, we need to decide where the support will come from. It can
either be rolled into the paging mechanism, or it can be applied by
the instructions themselves. I don't think it makes a difference as
far as behavior, but putting it in the paging mechanism seems like a
more logical place.




The instructions apply the segment base and the tlb handles all the
other details. There is currently no mechanism in place to let the
target software change the segmentation registers.

More information can be found at the following URL:
http://www.m5sim.org/flyspray/task/230

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