From mboxrd@z Thu Jan  1 00:00:00 1970
From: lm@mcvoy.com (Larry McVoy)
Date: Mon, 27 Nov 2017 08:50:46 -0800
Subject: [TUHS] Harvard and Von Neumann Architectures and Unix
In-Reply-To: <20171127161141.2C9E318C08F@mercury.lcs.mit.edu>
References: <20171127161141.2C9E318C08F@mercury.lcs.mit.edu>
Message-ID: <20171127165046.GD3430@mcvoy.com>

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?