[TUHS] Harvard and Von Neumann Architectures and Unix

Tim Bradshaw tfb at tfeb.org
Wed Nov 29 00:55:46 AEST 2017


On 27 Nov 2017, at 16:11, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
> 
> Along those lines, I was wondering about modern OS's, which I gather for
> security reasons prevent execution of data, and prevent writing to code.
> 
> Programs which emit these little 'custom code fragments' (I prefer that term,
> since they aren't really 'self-modifying code' - which I define as 'a program
> which _changes_ _existing_ instructions) must have some way of having a chunk
> of memory into which they can write, but which can also be executed.

I think, however this is done, it must be relatively tractable, because Lisp systems with native-code compilers work fine on modern OSs, and they do very much more than generate small code fragments.

--tim

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