[TUHS] Some resources for V6/PDP/SIMH newbs like me

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Nov 21 09:08:06 AEST 2017


    > From: Will Senn

    > (e) UNIX assembler uses the characters $ and "*" where the DEC 
    > assemblers use "#" and "@" respectively.

Amusing: the "UNIX Assembler Reference Manual" says:

  The syntax of the address forms is identical to that in DEC assemblers,
  except that "*" has been substituted for "@" and "$" for "#"; the
  UNIX typing conventions make "@" and "#" rather inconvenient.

What's amusing is that in almost 40 years, it had never dawned on me that
_that_ was why they'd made the @->*, etc change! "Duhhhh" indeed!

Interesting side note: the UNIX erase/kill characters are described as being
the same as Multics', but since Bell pulled out of the Multics project fairly
early, I wonder if they'd used it long enough to get '@' and '#' hardwired
into their fingers. So I recently has the thought 'Multics was a follow-on to
CTSS, maybe CTSS used the same characters, and that's how they got burned in'.
So I looked in the "CTSS Programmer's Guide" (2nd edition), and no, according
to it (pg. AC.2.02), the erase and kill characters on CTSS were '"' and
'?'. So, so much for that theory!


    > (l) The names "_edata" and "_end" are loader pseudo variables which 
    > define the size of the data segment, and the data segment plus the bss 
    > segment respectively.

That one threw me, too, when I first started looking at the kernel!

I don't recall if I found documentation about it, or just worked it out: it is
in the UPM, although not in ld(1) like one might expect (at least, not in the
V6 UPM; although in V7: 

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/man/man1/ld.1

it is there), but in end(3):

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/man/man3/end.3

	Noel


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