unexplained cores after compiles

[was-John McMillan]

In article <3986 at cbnews.ATT.COM> res at cbnews.ATT.COM (Robert E. Stampfli) writes:
>I have noticed that occasionally I will get a core dump immediately after
>invoking a program on the Unix-PC, usually upon trying to run it after
>it has just finished compiling.  Simply reinvoking the program without
>any changes results in it running fine.  This can not be attributed to a
>hardware glitch, as I have seen this on at least three machines I have access
>to.  Each has different disks, memory configuration, etc.  They were,
>however, all running version 3.5 of the Unix-PC operating system. 
			      ^^^
O sigh.  Amongst the wonders of the world are the incredibly perverse
ways in which Virtual Memory has been created.  {Expletives deleted}

The 3B1 paging (VM) software was developed, by Convergent Technologies,
from Berkeley concepts -- or so the documentation suggests.  If that
was so, the eventual Berkeley VM re-writes were well justified.  It is
too awful in its spaghettiosity [;-)] to believe, comprehend, or
meaningfully alter.  However:

	One defect was an erroneous line in the context-switcher
	-- supported by misleading commenting -- that produced
	errors when a shared-memory [SM] process swapped out and
	the new process had text overlapping the previous SM
	address- space.  This error was identified (what phun)
	and fixed (trivial) AFTER the 3.51 release.

Other than the above, it's probably YOUR own fault! %-)
However, relatively little use is made of indirect jumps that occur
in DATA (ie., changable) space, so I presume you've hit IT.

WORKAROUND:	Move your Shared Memory to a high, declared address
		-- where it cannot reasonable collide with TEXT or
		stack.

I'm still NOT satisfied with the 3.51c kernel, and the broader
3.51C system-wide fix-disk seems to be held off until other
anomalies are fixed.

jc mcmillan	-- att!mtunb!jcm	-- o my, what pretty flames those are!