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- Newsgroups: comp.os.linux
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!usenet.ins.cwru.edu!agate!boulder!caesar!drew
- From: drew@caesar.cs.colorado.edu (Drew Eckhardt)
- Subject: Re: Does Linux use segmentation?
- Message-ID: <1992Nov11.082654.5672@colorado.edu>
- Sender: news@colorado.edu (The Daily Planet)
- Nntp-Posting-Host: caesar.cs.colorado.edu
- Organization: University of Colorado at Boulder
- References: <1992Nov11.011359.27473@cbnewse.cb.att.com>
- Date: Wed, 11 Nov 1992 08:26:54 GMT
- Lines: 30
-
- In article <1992Nov11.011359.27473@cbnewse.cb.att.com> sph1@cbnewse.cb.att.com (stephen.p.hill) writes:
- >
- >I get the impression that Linux uses combined paging and
- >segmentation, in fact that nearly all modern OSs use
- >the combination. Is this true?(the part about Linux)
-
- If you're talking about the implementation of Linux on the i386,
- this is correct. Segmentation allows the kernel to access it's
- address space, and a user process space independantly of eachother,
- without mapping the user space into kernel space someplace and doing
- pointer scrambling.
-
- When in kernel code, es,ds,ss, and cs point to the kernel's address space,
- while fs points to the address space of the user process.
-
- Earlier versions of Linux used a single, system-wide set of page tables,
- with the segments in each processes' LDT selecting an appropriate
- offset into the 4G virtual address space, with a 64M limit.
-
- From a user perspective, segmentation isn't there. Each process
- has a flat 3G bit address space, with the cs, ds, es, and ss selectors
- only serving to select descriptors with appropriate permissions for
- access with that segment register (ie, cs segment must be executable,
- ds must be writeable) to the same flat address space.
-
-
- --
- Boycott AT&T for their absurd anti-BSDI lawsuit. | Drew Eckhardt
- Condemn Colorado for Amendment Two. | drew@cs.colorado.edu
- Use Linux, the fast, flexible, and free 386 unix |
-