Reason for different segments in Linux on x86

Posted by anjruu on Stack Overflow See other posts from Stack Overflow or by anjruu
Published on 2011-01-01T18:01:56Z Indexed on 2011/01/01 18:54 UTC
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linux-kernel

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segmentation

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segments

Hey all,

So, I know that Linux uses four default segments for an x86 processor (kernel code, kernel data, user code, user data), but they all have the same base and limit (0x00000000 and 0xfffff), meaning each segment maps to the same set of linear addresses.

Given this, why even have user/kernel segments? I understand why there should be separate segments for code and data (just due to how the x86 processor deals with the cs and ds registers), but why not have a single code segment and a single data segment? Memory protection is done through paging, and the user and kernel segments map to the same linear addresses anyway.

Thanks!

anjruu

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