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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: is there a version of unix written in Ada
Date: Thu, 1 Oct 2020 16:54:09 -0500
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"Paul Rubin" <no.email@nospam.invalid> wrote in message 
news:87o8lml1md.fsf@nightsong.com...
...
>> Are you going to recompile and re-link everything in
>> absolute addresses every time anything changes and then reboot?
>
> Position independent code is a thing.

Sure, but it's impractical on the Intel architectures as the machines are 
too register-poor to use them unnecessarily.

Besides, it doesn't seem necessary; the loader can translate addresses when 
an executable is installed. (That's commonly done in .EXE files.) Most data 
is indirectly accessed anyway (stack or heap based), so the actual address 
it lives at isn't relevant (and the rest can be translated when loading).

Dmitry said:
> You either have abstraction, like flat contiguous address space, however 
> implemented, or you do not.

Flat address spaces are greatly overrated. It's much better to organize 
programs as a series of separate segments anyway. No one should be reading 
code or executing data anyway, so why should they share an address space?? 
The problem with 1980's segments was that they were too small, requiring 
lots of juggling of segments, but that's not a problem on more modern 
architectures.

To me, a "flat address space" is precisely destroying abstraction. Code /= 
Data and they should not be treated the same. (Many of the problems with 
malware occur precisely because it is easy to execute data.).

                      Randy.