Re: Pointless Nostalgia: System Service Dispatching

Newsgroups	comp.os.vms
Subject	Re: Pointless Nostalgia: System Service Dispatching
References	(3 earlier) <nl3491$rou$1@Iltempo.Update.UU.SE> <00B0B657.24DF3378@SendSpamHere.ORG> <nl3r1k$f2f$1@Iltempo.Update.UU.SE> <00B0B66F.E33DC123@SendSpamHere.ORG> <00B0B6FD.93802360@SendSpamHere.ORG>
From	VAXman- @SendSpamHere.ORG
Message-ID	<00B0B803.8FB98ACE@SendSpamHere.ORG> (permalink)
Organization	c.2016 Brian Schenkenberger. Prior employers of copyright holder and their agents must first obtain written permission to copy this posting.
Date	2016-07-02 20:02 +0000

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In article <c24a9ad7-4198-46cd-bc4f-5268690e186e@googlegroups.com>, lawrencedo99@gmail.com writes:
>On Saturday, July 2, 2016 at 12:46:53 AM UTC+12, VAXman- wrote:
>> In article <nl5mlr$1ou$1@Iltempo.Update.UU.SE>, Johnny Billquist writes:
>>>So could you confirm that VMS backs up the PC and re-execute the system=
>=20
>>>call sometimes?
>>=20
>> I don't believe that's so.  The only way back home, so to speak, is via t=
>he
>> REI instruction.  That pops the saved PC/PSL from the stack, restoring  t=
>he=20
>> original mode and execution resumes at the next instruction after the CHM=
>x.
>
>Time to re-read the Internals and Data Structures Manual?
>
>On VAX, the procedure for executing a restartable system service (e.g. $HIB=
>ER, $WAITFR, $SYNCH) goes broadly something like this (omitting irrelevant =
>detail which I can=E2=80=99t remember anyway):
>
>* Set the relevant PCB state and put the PCB on the relevant wait queue.
>* Subtract 4 from the saved PC on the stack.
>* Save the current process context and go find another process to make curr=
>ent.
>
>So when the process gets made current again, the CHMK instruction, and henc=
>e the system call, is re-executed. If the condition it was waiting for has =
>not occurred yet, it goes right back onto the wait queue again. Otherwise, =
>it resumes execution.
>
>It=E2=80=99s that =E2=80=9Csubtract 4=E2=80=9D I found inelegant...

One byte instruction, one byte operand specifier, two bytes for the CHMx operand.
That looks like 4 bytes to me.
-- 
VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG

I speak to machines with the voice of humanity.

Thread

Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-06-29 02:53 -0700
  Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-06-29 13:36 +0200
    Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-06-29 16:05 -0700
      Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-06-30 14:45 +0200
        Re: Pointless Nostalgia: System Service Dispatching moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-06-30 16:53 +0000
          Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-06-30 15:32 -0700
        Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-06-30 16:55 +0000
          Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-06-30 21:13 +0200
            Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-06-30 19:52 +0000
              Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-07-01 14:11 +0200
              Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-01 12:46 +0000
                Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-07-01 17:40 +0200
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-01 16:59 +0000
                Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-07-01 19:45 +0200
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-01 20:01 +0000
                Re: Pointless Nostalgia: System Service Dispatching Johnny Billquist <bqt@softjar.se> - 2016-07-04 12:35 +0200
                Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-07-01 15:18 -0700
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-02 20:02 +0000
                Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-07-03 14:10 -0700
                Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-07-04 14:56 -0700
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-04 13:25 +0000
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-05 00:46 +0000
                Re: Pointless Nostalgia: System Service Dispatching David Froble <davef@tsoft-inc.com> - 2016-07-05 08:43 -0400
                Re: Pointless Nostalgia: System Service Dispatching lawrencedo99@gmail.com - 2016-07-05 15:40 -0700
                Re: Pointless Nostalgia: System Service Dispatching Paul Sture <nospam@sture.ch> - 2016-07-06 07:33 +0200
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-06 00:08 +0000
                Re: Pointless Nostalgia: System Service Dispatching David Froble <davef@tsoft-inc.com> - 2016-07-05 22:57 -0400
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-06 10:43 +0000
                Re: Pointless Nostalgia: System Service Dispatching Paul Sture <nospam@sture.ch> - 2016-07-05 12:30 +0200
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-05 13:00 +0000
                Re: Pointless Nostalgia: System Service Dispatching Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2016-07-06 15:12 +0000
                Re: Pointless Nostalgia: System Service Dispatching Paul Sture <nospam@sture.ch> - 2016-07-06 21:50 +0200
                [OT] Real Genius, was: Re: Pointless Nostalgia: System Service Dispatching Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2016-07-07 19:55 +0000
                Re: [OT] Real Genius, was: Re: Pointless Nostalgia: System Service Dispatching Paul Sture <nospam@sture.ch> - 2016-07-07 22:27 +0200
                Re: Pointless Nostalgia: System Service Dispatching   VAXman-  @SendSpamHere.ORG - 2016-07-06 15:42 +0000

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