[Simh] PDP-11 GCC cross-assembler... posible bug... or is just me?

[Johnny Billquist]

On 2012-08-16 20:49, Jordi Guillaumes i Pons wrote:
> Hi list,
>
> I've jumped into what seems to be a bug in the gnu binutils assembler.
> I've already submited a report:
>
> http://sourceware.org/bugzilla/show_bug.cgi?id=14480
>
> To cut the story short, the assembler does not trigger deferred indirect
> mode unless the index is specifically written in the instruction. So
> this instruction:
>
>      JSR    PC,@(R0)
>
> Assembles exactly equal that this one:
>
>      JSR    PC,(R0).
>
> If the source code is:
>
>      JSR    PC, at 0(R0)
>
> then the assembled code is correct.
>
> The problem with this bug (if it is really a bug) is the gcc compiler
> generates the incorrectly handled instruction if you try to use a
> function pointer table and enable size optimization (-Os option).
>
> The other possibility is I'm not understanding at all the PDP-11
> addressing modes and the assembler is working as it should do... Could
> anyone enlighten me about this?

Well, using the DEC notation for PDP-11 assembler language, @(R0) and 
(R0) are indeed two different things, and you seem to have understood it 
perfectly right.
Not sure if gas might have its own ideas about notation though...

	Johnny