sr (nobody.delete@this.nowhere.com) on September 22, 2021 1:00 pm wrote:
> Linus Torvalds (torvalds.delete@this.linux-foundation.org) on September 22, 2021 11:50 am wrote:
>
> > The only time segments are useful is if they give you added capabilities. And no, "limiting access"
> > is not really an added capability from a user standpoint, despite how many computer architects
> > want to do it. You need to give people something, and in that context you can then add permissions
> > as a part of the parcel. Not just say "this adds no other value than limit you".
>
> And you consider that limiting possibility isn't added capability? I remember that some twenty
> years ago certain OS did keep nagging to me that defaulting user access to superuser is stupid.
> Didn't care because why would I want to limit my own access to my personal computer.
>
>
> Hardware possibilities is another take - I personally view segmentation purely from software standpoint.
> Isn't mixing code, data and scratch into one linear address space also be pure stupidity? Even more with
> today as most of user code isn't coming directly from programmer but instead through many layers of abstraction
> and libraries - one can newer be really sure what his code exactly does. So being able to configure hardware
> limits into different categories or objects is obvious huge advantage for code rigidity.
>
> That early 80's segmentation model is of course closely related to C++ and with modern view
> some modifications might be preferred - but as hardware solution isn't being able to configure
> process address space to many smaller independently limited areas still preferred - cutting
> them into different address spaces would be surely bad for performance in all possible ways?

Not sure of what you mean by the statement in bold, but if you want "a single code segment, a single data segment, a single stack segment", it is going to be difficult to manage all the shared libraries and their allocations - without a page table per segment.
Then you look at multiple threads and wonder how to handle.
Then you begin to look at fork() and forget the initial idea...