Re: VAX addressing modes

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> Duh, somehow I failed to copy & paste big parts of the data I
> collected into the original message - sorry.

:-(  I've done such things often enough.

> In objdump -dR output, the code looks like:

>    5ca00:       31 de db        brw 5a5e1 <Perl_yylex+0x2e6f>
>    5ca03:       cf 50 00 0a     casel r0,$0x0,$0xa
>    5ca07:       27 11 38 45     divp $0x11,$0x38,$0x14[r5],*0xffffd214(r2),*0x46
> (r0),*0x46(r0)
>    5ca0b:       14 d2 14 d2 
>    5ca0f:       b0 46 b0 46 

This is pretty obviously not code (that divp makes no sense).  The
disassembler is defective; it is failing to understand that casel is
followed by a jump table, not ordinary code.  This should be
disassembled as something more like this (this is what my disassembler
produced when fed the relevant binary; I've manually reinserted the
relocation line and the hex memory contents):

         5ca03: cf 50 00 0a casel   r0,$0,$a
         5ca07: 27 11       case -> 0x5db2e
         5ca09: 38 45       case -> 0x60f3f
         5ca0b: 14 d2       case -> 0x59c1b
         5ca0d: 14 d2       case -> 0x59c1b
         5ca0f: b0 46       case -> 0x610b7
         5ca11: b0 46       case -> 0x610b7
         5ca13: 95 12       case -> 0x5dc9c
         5ca15: 95 12       case -> 0x5dc9c
         5ca17: 19 00       case -> 0x5ca20
         5ca19: 14 d2       case -> 0x59c1b
         5ca1b: 38 45       case -> 0x60f3f
         5ca1d: 31 06 00    brw     0x5ca26
         5ca20: 17 9f cf 76 jmp     *$000676cf
                06 00
                        5ca22: R_VAX_RELATIVE   *ABS*+0x676cf
         5ca26: dd 5a       pushl   r10

> (and I don't want to think about the duplicate tstb $0x12 right now)

That's explained by their not being tstb instructions at all.  Those
are the case displacements to 0x5dc9c.

The relocation also makes a whole lot more sense now, at least to me.

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