ioccc/1984/mullender/index.html

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<h1 id="the-grand-prize">The Grand Prize</h1>
<p>Sjoerd Mullender</p>
<p>Robbert van Renesse</p>
<h2 id="judges-comments">Judges’ comments:</h2>
<p>NOTE: This entry is likely to fail and/or dump core on modern
computers.</p>
<p>Without question, this C program is the one of the most obfuscated C
program that has ever been received! Like all great contest entries,
they result in a change of rules for the following year. To prevent a
flood of similar programs, we requested that programs be non machine
specific.</p>
<p>This program was selected for the 1987 t-shirt collection.</p>
<blockquote>
<p>NOTE: If your machine is not a Vax-11 or pdp-11, this program will
not execute correctly. In later years, machine dependent code was
discouraged.</p>
</blockquote>
<p>The C startup routine (via crt0.o) transfers control to a location
named main. In this case, main just happens to be in the data area. The
array of shorts, which has been further obfuscated by use of different
data types, just happens to form a meaningful set of PDP-11 and Vax
instructions. The first word is a PDP-11 branch instruction that
branches to the rest of the PDP code. On the Vax main is called with the
calls instruction which uses the first word of the subroutine as a mask
of registers to be saved. So on the Vax the first word can be anything.
The real Vax code starts with the second word. This small program makes
direct calls to the write() Unix system call to produce a message on the
screen. Can you guess what is printed? We knew you couldn’t! :-)</p>
<p>Copyright (c) 1984, Landon Curt Noll. All Rights Reserved. Permission
for personal, educational or non-profit use is granted provided this
this copyright and notice are included in its entirety and remains
unaltered. All other uses must receive prior permission in writing from
both Landon Curt Noll and Larry Bassel.</p>
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