Path: utzoo!mnetor!uunet!unisoft!mtxinu!ed
From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: comp.unix.wizards
Subject: Re: Aliasing text and data segments of a process
Message-ID: <555@mtxinu.UUCP>
Date: 21 Jan 88 16:56:39 GMT
References: <202@sdti.UUCP>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley
Lines: 22

>Is there a way in Unix to create an "alias" between the text and data
>segments of a process?  More specifically, how does one go about executing a
>block of code that was generated in a data segment?

It depends on the hardware architecture and on the implementation of
the operating system.  Some hardware (e.g., some PDP-11 models) allows
for a strict separation of instruction ("text") and data spaces.  On such
a machine, if the OS uses the feature, then (unless the text space is
writable, which it typically isn't) you're out of luck.

Other machines, like the VAX, do not rigidly separate instruction
and data spaces.  Even in this class of machinem though, there may
be pitfals:  If the hardware has separate read and execute permissions
on regions of memory, then the same problem arises.  If the OS does
not supply execute permission for the data segment, then code can't
be executed from there.

-- 
Ed Gould                    mt Xinu, 2560 Ninth St., Berkeley, CA  94710  USA
{ucbvax,uunet}!mtxinu!ed    +1 415 644 0146

"`She's smart, for a woman, wonder how she got that way'..."