[TUHS] Harvard and Von Neumann Architectures and Unix

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Nov 28 03:11:22 AEST 2017


    > From: Larry McVoy

    >> they aren't really 'self-modifying code' - which I define as 'a program
    >> which _changes_ _existing_ instructions

    > Isn't that how dtrace works?

I'm not familiar with dtrace(), but if it modifies some other routine's code,
then it would not be "self" modifying, right?


Oh, another category, sort of like biological viruses (which are in a grey
zone between 'alive' and not): the PDP-11 paper tape bootstrap:

  http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/bootloader.mac

in which the program's own code _is_ modified - but not by program
instructions, but by data on the paper tape it is reading in. It's
entertainingly convoluted (the copy above should be well-enough commented to
make it pretty easy to understand what's going on).

     Noel


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