Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!mit-eddie!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.arch
Subject: Re: Software Distribution
Message-ID: <5655@june.cs.washington.edu>
Date: 6 Sep 88 17:58:29 GMT
Article-I.D.: june.5655
References: <891@taux01.UUCP> <28200195@urbsdc>
Reply-To: pardo@uw-june.UUCP (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 68

>>>[ portable intermediate representation ]

>pardo@cs.washington.edu writes:
>>How about C, the portable assembler?  :-) :-) :-)

aglew@urbsdc.Urbana.Gould.COM writes:
>[ High-level IR (intermediate representation) needed for distribution ]
>[ The customer can modify C too easily ]

I'll claim that I can pretty easily write a program that takes
ordinary C programs and makes them gosh-almighty hard to understand.
Here are some things I can do:

* Change names so that none of them are meaningful.
* Perform function inlining so that content is replicated (e.g., hard
  to find).
* Use random rewrite rules to change the structure of native
  constructs so that the code has no apparant style.
* Intentionally include dead code that is removed by the optimizer.
* Perform non-local data motion.
* Study the Obfuscated C Code competition very closely :-)

As a simple example:

    void
foo(n)
    int		n;
{
    int		i;

    for (i=0; i<n; ++i)
	howdy( "Hello, world\n" );
}


    void
x(p)
    int		p;
{
    const char	*m = "Hello, world\n";
    int		r;
    int		z;

    r = p;
loop:
    if (r>=p)
	return;
    else {
	a (m), z=r++;
	goto loop;
    }
    a (z);
    exit (0);
}

A fair optimizer should make the same code for both.  Now C is
probably sub-optimal for some (language) distributions, but you can
perform the same "tricks" with nearly any language.

BTW, I have a tool that takes unoptimized (.o) output from pcc on a
VAX and turns it back into something close to the original code.
Having a high-level IR may not gain the vendors anything over an
existing "standard" such as C.

	    ;-D on  ( Clear as a bell )  Pardo
-- 
		    pardo@cs.washington.edu
    {rutgers,cornell,ucsd,ubc-cs,tektronix}!uw-beaver!june!pardo