[TUHS] origins of void*

Noel Chiappa jnc at mercury.lcs.mit.edu
Mon Nov 6 01:43:06 AEST 2017


    > From: Clem Cole

    > typing hard started to become more important in the kernel.

I can imagine! The V6 kernel had all sorts of, ah, 'unusual' typing - as I
learned to my cost when I did that hack version of 'splice()' (to allow a
process in a pipline to drop out, and join the two pipes together directly),
which I did in V6 (my familiar kernel haunt).

Since a lot of code does pointer math to generate wait 'channel' numbers,
e.g.:

  sleep(ip+2, PPIPE);
  
when I naively (out of habit) tried to declare my pointers to be the correct
type, the math didn't work any more! ('ip', in this particular case, was
declared to be an 'int *'.)

No doubt part of this was inherited from older versions (of the system, and
C); the code was working, and there was no call to tweak it. The lack of
casts/coercion in the V6 C compiler may have been an issue, too - I had to do
some equally odd things to make my splice() code work!

	Noel


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