From:	MERC::"uunet!WKUVX1.BITNET!goathunter" 25-JAN-1993 19:33:34.82
To:	alpha-ids@WKUVX1.BITNET
CC:	GAVRON@ACES.COM
Subj:	For your info: reference problem in system spce

Date sent:  25-JAN-1993 17:08:13


DEC has successfully duplicated my problem and is researching a
solution where
        macro32                         dec c
        ------------------------------------------------------
        movl (r7),r8                    p = *q
        r8 ends up = r7, not (r7)       p ends up =q, not *q

        If you want to have fun with this yourself, try this
        on an ALPHA running VMS:

        main()
        {
                int ini$brk;            /* Where the breakpoint vector is */
                int *p,*q;
                int opcode;

                p = (int *)ini$brk;     /* The ini$brk vector address in p */
                p += 2;                 /* The address of the ini$brk code */
                q = (int *)*p;          /* Q points to code */

                /* Now here a debugger will let you see that Q is something
                   like 8000204C and *Q is the 477F... opcode!  */

                opcode = *q;


                /* Now here you'd expect that opcode would be 477F... just
                   like the debugger figured.  BZZT, wrong, actually opcode
                   now equals Q!!!  Arghh!!! */

                }


        The same problem is trivial to duplicate in MACRO32:
        .entry  bogon,^m<>
        movl    #ini$brk,r6     ; Address of INI$BRK vector
        addl    #8,r6           ; Address of INI$BRK code address
        movl    (r6),r7         ; Address of first bytes of code
        movl    (r7),r8         ; Now R8 SHOULD be the opcode but
                                ; instead it's the same as R7.  WHY!!!!!????!!
        .end    bogon



        Ehud

--
Ehud Gavron     (EG76)
gavron@Spades.ACES.COM