Re: CMS abend caused by cmd "discard" at sixpack 1.2

> DMSITP143T SPECIFICATION EXCEPTION OCCURRED AT 0176D6 IN SYSTEM
> ROUTINE  Î     ,
> RE-IPL CMS.
> CP ENTERED; DISABLED WAIT PSW '00020000 4001B436'

This looks to be a minor bug in DMSCPF HRC350DS, which adds
support for commands of the form:

        FIFO | LIFO | DISCARD cpcommand

If you say "DISCARD " with a trailing blank, it works.  If
you say "DISCARD" without the blank, you get the pic6.  The
code doesn't correctly handle the possibility of one of
FIFO|LIFO|DISCARD with nothing at all after the initial
word.  For "DISCARD", it does:

         CLC   0(8,R2),DISCARD is it 'DISCARD'
         BNE   NORMAL         nope
         SR    R6,R6          remember DISCARD
         LA    R2,8(R2)       skip past 'DISCARD '
         S     R3,EIGHT       decrement CP command length

then tests the length of the remaining command text:

         LTR   R3,R3          anything left in the buffer?
         BZ    WRAPUP         no

except that the length register, R3, contains X'7FFFFFFF'
rather than zero, so the test doesn't catch the absence of
any CP command to be issued and doesn't branch around the
diagnose X'0008'.  CP fails the diagnose with a pic6
because of the invalid length.

A couple of things.  One is that R3 already contains the
flag bits to be passed to diagnose in the high-order bits,
which might screw up the length arithmetic if the bits are
anything but zero.  The other is that the "anything left in
the buffer" test needs to ensure the remaining length is positive,
not just non-zero, because if there isn't any data after the
first token, subtracting the expected length of the token
plus one will make the length go negative.

-- 
Kevin