gas 2.8.1 CPU32 bug (Was: as: unrecognized option `-c68020')

Robin Kirkham
Thu Oct 23 01:06:00 GMT 1997

On Wed, 22 Oct 1997, Mark Phillips wrote:
> Are you sure your patch is completely correct? 
> My reading of the Motorola manuals is that, of the 020/030/040
> addressing modes only (bd,An,Xn) and (bd,PC,Xn) are supported by the CPU32
> and then only for word and long accesses. Your patch appears to allow all
> the 020/030/040 modes and any width?!

I believe it is correct, although it might be right for the wrong reason 8-)
--I don't fully understand the operand mode hieroglyphics in the opcode table.

I did try some experiments, however.

The address mode must subsequently checked against processor type by gas,
because (with my patch) it correctly rejects the four 020/030/040 modes that
the CPU32 doesn't handle: ([bd,An,Xn],od), ([bd,An],Xn,od), ([bd,PC,Xn],od)
and ([bd,PC],Xn,od). It accepts all the modes I think it should.

The byte restriction you mention applies only to the An mode, i.e. "tst.b %a0"
is illegal (for all 68k's I think). Again, gas seems to have it right.

The only wrinkle might be "tst.b #<data>". My 020 manual says this is illegal,
but gas accepts it for 020 and CPU32. It also executes on the 040 and CPU32
(I don't have an 020 that still works). So, gas may be right here: I can't
tell. (Not a very useful instruction, anyway).

	Addr Mode		Mode/Register	Processors
	Dn			000 n		020 cpu32
	An			001 n		020 cpu32 (not tst.b)
	(An)			010 n		020 cpu32
	(An)+			011 n		020 cpu32
	-(An)			100 n		020 cpu32
	(d16,An)		101 n		020 cpu32
	(d8,An,Xn)		110 n		020 cpu32
	(bd,An,Xn)		110 n		020 cpu32
	([bd,An,Xn],od)		110 n		020
	([bd,An],Xn,od)		110 n		020

	(xxx).W			111 000		020 cpu32
	(xxx).L			111 001		020 cpu32
	#<data>			111 100		020 cpu32 (not tst.b ???)
	(d16,PC)		111 010		020 cpu32
	(d8,PC,Xn)		111 011		020 cpu32
	(bd,PC,Xn)		111 011		020 cpu32
	([bd,PC,Xn],od)		111 011		020
	([bd,PC],Xn,od)		111 011		020

> Does anyone know what the offical patch is that made it into the beta
> binutils?

It seems to be the same as mine...

> I used a much more paranoid patch to solve the problem, I JUST allowing
> the (bd,An,Xn) mode - the (bd,PC,Xn) mode was not causing me a problem.

Don't you mean An mode? Correct me if I am wrong, but this seems to be what
you patch adds (and which was the start of all this anyway).

Robin Kirkham			CSIRO Manufacturing Science and Technology
Project Engineer		Locked Bag 9, Preston 3072, Australia	Phone: +61 3 9662-7756  Fax: +61 3 9662-7851

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