ISA checks for factories

ISA checks for factories

[Phil Muldoon]

I've written several factories to decide what class to instantiate 
depending on the ISA. These usually end up as hacks, probably because I 
do not understand something quite right, or there is no real decent  
"What ISA does this task/proc belong" discovery.

I can instance check an ISA with:

Isa isa = proc.getIsa();
if (isa instanceof IsaIA32) ....

and so on, but that will not work for 32 on 64 ISAs. For example, on a 
32 bit process on a 64 bit system, the instance returned would be

LinuxIa32On64

And those cannot be instance checked as they are package private, while 
the "native" ISAs are public.

So what is the solution here? Open the scope of the xxOnxx ISAs? I get 
the feeling that instanceof checks tell me that we need to work on a 
better solution anyway. Reverting to reflection screams hack to me.

Regards

Phil

Re: ISA checks for factories

[Andrew Cagney]

Phil,

unfortunate timing, we crossed e-mails during the night,

Phil Muldoon wrote:
> I've written several factories to decide what class to instantiate 
> depending on the ISA. These usually end up as hacks, probably because 
> I do not understand something quite right, or there is no real decent  
> "What ISA does this task/proc belong" discovery.
>
> I can instance check an ISA with:
>
> Isa isa = proc.getIsa();
There is now also:
    ISA isa = task.getISA()
which returns a frysk.isa.ISA, which looks smells and behaves like an 
ENUM.  This new ISA just the following attributes:
   - family (i386, x8664, PPC)
   - word size (4, 8)
   - byte order (little, big)
leading to the combinations: IA32, X8664, PPC32LE, PPC32BE, PPC64LE, 
PPC64BE.

> if (isa instanceof IsaIA32) ....

It can then be used as either:

    if (isa == ISA.IA32)
      ..
    else if (isa = ISA.X8664)
      ..

or better?:

   ISAMap map = new ISAMap("why am I here")
       .put(ISA.IA32, new My(IA32))
       .put(ISA.X8664, new My(X8664))
       ;
   ...
       // Throws a RuntimeException if ISA missing
       My o = (My) map.get(task.getISA);

which could easily be wrapped up in a factory.

Andrew


>
> and so on, but that will not work for 32 on 64 ISAs. For example, on a 
> 32 bit process on a 64 bit system, the instance returned would be
>
> LinuxIa32On64
>
> And those cannot be instance checked as they are package private, 
> while the "native" ISAs are public.
>
> So what is the solution here? Open the scope of the xxOnxx ISAs? I get 
> the feeling that instanceof checks tell me that we need to work on a 
> better solution anyway. Reverting to reflection screams hack to me.
>
> Regards
>
> Phil

Re: ISA checks for factories

[Phil Muldoon]

Andrew Cagney wrote:
> Phil,
>
> There is now also:
>    ISA isa = task.getISA()
> which returns a frysk.isa.ISA, which looks smells and behaves like an 
> ENUM.  This new ISA just the following attributes:
>   - family (i386, x8664, PPC)
>   - word size (4, 8)
>   - byte order (little, big)
> leading to the combinations: IA32, X8664, PPC32LE, PPC32BE, PPC64LE, 
> PPC64BE.
>

Ok that makes sense, I got that from the original email, but ...


> or better?:
>
>   ISAMap map = new ISAMap("why am I here")
>       .put(ISA.IA32, new My(IA32))
>       .put(ISA.X8664, new My(X8664))
>       ;
>   ...
>       // Throws a RuntimeException if ISA missing
>       My o = (My) map.get(task.getISA);
>
>
I'm still a little fuzzy on how it can be used to detected IA 32 on 64, 
or PPC32 On 64?

Regards

Phil

Re: ISA checks for factories

[Phil Muldoon]

Phil Muldoon wrote:
> I'm still a little fuzzy on how it can be used to detected IA 32 on 
> 64, or PPC32 On 64?
>

Answering my own question. I looked at the code, and it appears that 
Task.getISA() will return the contextually correct ISA for the situation 
in hand. So for a 32bit process on x8664 it will return the 32 bit ISA 
and so on. Previously one had to instance check the ISA as a 32On64 ISA 
was returned explicitly.

I'll rewrite the LinuxCorefileFactory to use this new method now.

Regards

Phil