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From: duk@vu44.UUCP
Newsgroups: net.lang.c
Subject: labels and self-modifying code
Message-ID: <385@vu44.UUCP>
Date: Fri, 7-Sep-84 18:52:24 EDT
Article-I.D.: vu44.385
Posted: Fri Sep  7 18:52:24 1984
Date-Received: Sun, 16-Sep-84 07:48:17 EDT
Organization: VU Informatica, Amsterdam
Lines: 39

Who needs assembler when you can use C to write illegible, self-modifying
code. The program below, slightly adapted from a program by Jack Jansen,
compiles and "works" on our PDP11/44 running Unix V7.

--------------------------------------------------------------------------
#include <stdio.h>

main() {

    func(0);
    func(1);
}

func(arg) int arg; {

    int *jumptab[2];

    goto endofit; /* cannot use &label before it's defined */
lab0:
    printf("Lab 0\n");
    return;
lab1:
    printf("Lab 1\n");
    return;
lab2:
    "Lab 2\n";
endofit:
    jumptab[0] = lab0;
    jumptab[1] = lab1;
    *(jumptab[0] + 1) = *(lab2 + 1);
    goto jumptab[arg];
}
--------------------------------------------------------------------------

You shouldn't give any of the options -i, -n (evidently), or -O to cc.
When you give the -O flag, the optimizer throws the labels away since they
are not used (it *thinks* the're not used!), and then later ld can't find them.

				Duk Bekema