[TUHS] Harvard and Von Neumann Architectures and Unix

Lawrence Stewart stewart at serissa.com
Tue Nov 28 04:21:25 AEST 2017


> On 2017, Nov 27, at 12:08 PM, Clem Cole <clemc at ccc.com> wrote:
> 
> SPICE2 does the same sort of thing (in semi-portable Fortran-IV)
> 
> On Mon, Nov 27, 2017 at 11:50 AM, Larry McVoy <lm at mcvoy.com <mailto:lm at mcvoy.com>> wrote:
> On Mon, Nov 27, 2017 at 11:11:41AM -0500, Noel Chiappa wrote:
> >     > From: Doug McIlroy
> >
> >     > But if that had been in D space, it couldn't have been executed.
> >
> > 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.
> 
> Isn't that how dtrace works?
> 

In POSIX systems, the mprotect(2) syscall can set execute permissions.


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