[TUHS] Another odd comment in V6

Paul Ruizendaal pnr at planet.nl
Tue Feb 14 22:27:48 AEST 2017


Hi Nick,

Many thanks for that background!

I think the quote from the Gabriel paper indeed refers to software
interrupts, i.e. signals -- it would not make sense otherwise. The
ITS system that the MIT guy referred to is 'large', it ran on PDP10
mainframes.

I understand how executing a signal handler is piggy-backed on the
return from kernel mode. However, when the signal handler is
finished it could either continue with the next instruction or
re-excute the system call trap instruction. See
http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/src/sys/sys/trap.c
(towards end) for details how this is actually done in 2.9BSD.
I think you referred to that mechanism as well.

However, my question remains: why is that mysterious comment there,
above ttread() in V6, and is there a link with the Gabriel story?

Paul

On 14 Feb 2017, at 12:27 , Nick Downing wrote:

> Well I don't know about this actual conversation in history so I can't
> help with that. But I can describe how interrupted system calls work.
> [..more..]



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