Port-vax archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: VAX addressing modes



> At least I cannot find anything in the VAX Architecture Standard to
> claim that CASEx is not just a slightly complicated variant of an
> ordinary indexed PC-relative data load with the value retrieved added
> to the PC as the destination register.

And what part of that does not apply equally to BRW?  (Well, not
counting the "slightly complicated" part.)

> I see no reason for a jump table used with one of the CASEx
> instructions to be treated specially by a disassembler.

I do, at least when the third operand is an inline constant: it's more
useful that way.

I know I, at least, find it more useful to see

	1318:	casel	r0, $32, $4
	131c:	-> 1548
	131e:	-> 1607
	1320:	-> 1414
	1322:	-> 1414
	1324:	-> 1fc0
	1326:	movw	$12, *(r5)+
	1329:	tstb	r2
	132b:	blss	132d

than

	1318:	casel	r0, $32, $4
	131c:	.word	022c
	131e:	.word	02eb
	1320:	.word	00f8
	1322:	.word	00f8
	1324:	.word	0ca4
	1326:	movw	$12, *(r5)+
	1329:	tstb	r2
	132b:	blss	132d

and _much_ more useful than

	1318:	casel	r0, $32, $4
	131c:	movc5	$2, -07ff07fe(r11), $0, 0c(r4), *12(r0)
	1328:	tstb	*(r5)+

>> Starting disassembly in the middle of a CASE jump table is no
>> different from starting disassembly in the middle of any other
>> multi-byte instruction.  I would not expect a disassembler to look
>> backwards in either case.
> Symbol table annotation would at least tell the tool the stream
> requested is actually data, as well as where exactly the next
> instruction starts,

Or it could, y'know, recognize the CASE instruction and do it
automatically.  I don't see what's so undesirable about that.

If you want to annotate the displacement table so that disassembly
starting partway through it can recognize that it's in a CASE table,
fine, but I don't see that as any different from annotating the second
and later bytes of any multi-byte instruction to deal with the
analogous situation there.

/~\ The ASCII				  Mouse
\ / Ribbon Campaign
 X  Against HTML		mouse%rodents-montreal.org@localhost
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B


Home | Main Index | Thread Index | Old Index