Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!homxb!mhuxt!mhuxm!mhuxo!ulysses!allegra!mit-eddie!husc6!think!ames!aurora!labrea!decwrl!decvax!ima!minya!jc
From: jc@minya.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Aliasing text and data segments of a process
Message-ID: <452@minya.UUCP>
Date: 23 Jan 88 14:40:00 GMT
References: <202@sdti.UUCP> <730@umbc3.UMD.EDU> <7156@brl-smoke.ARPA>
Organization: home
Lines: 39

In article <7156@brl-smoke.ARPA>, gwyn@brl-smoke.ARPA (Doug Gwyn ) writes:
> In article <730@umbc3.UMD.EDU> alex@umbc3.UMD.EDU (Alex S. Crain) writes:
> >loads the .o file as data, and then branches to the start of the text area
> >of the .o file
> 
> This cannot possibly work on an architecture that enforces the
> distinction between Instruction and Data spaces.

Jeez, why do they let such obvious non-wizards post responses to
unix.wizards? (:-)  There have been far too many such comments from
people who obviously haven't RTFM, in this case K&R.

Study the following program, which should work anywhere you have
a C compiler.  (If your compiler doesn't do it right, send it back
to the factory; it's obviously broken.)

|	#include <stdio.h>
|	char *code;		/* This can point to any address in memory */
|	int (*fct)();	/* We will point this at *code */
|	
|	foobar(x,y)
|	{	printf("foobar(%d,%d)\n",x,y);
|		return x + y;
|	}
|	main()
|	{	int i;
|	
|		code = (char*)foobar;	/* This could be malloc() */
|		fct = (int(*)())code;	/* Stuff random pointer into fct */
|		i = (*fct)(7,9);		/* Call random memory location */
|		printf("(*fct)(7,9)=%d\n",i);
|		exit(0);
|	}

Well, OK, he asked if there is Unix support, and there isn't.
So who needs it?  This oughta work on VMS or MS/DOS, too.

-- 
John Chambers <{adelie,ima,maynard,mit-eddie}!minya!{jc,root}> (617/484-6393)