[Simh] fprint_sym and parse_sym limitation

[J. David Bryan]

On Friday, September 11, 2015 at 20:17, Paul Koning wrote:

> I'd do: if (cpu_reg[addr].flags & REG_IR) ...

OK, that's a reasonable approach.

You might wish to write an implementation of your idea.  I recall trying it 
myself when I was first looking into the issue, but it turned out to be 
reasonably complicated -- more so than passing register flags, which 
required changing only two of the fprint_sym calls as I have outlined while 
maintaining backward compatibility with existing simulators.

You mentioned getting the register array by working back from the UNIT 
pointer, but unfortunately, uptr is NULL in some cases, e.g., when called 
from ex_reg.  ex_reg receives a REG pointer but neither a unit pointer or a 
device pointer.  It could be added, of course.

Also, it's not clear how to derive the register index in ex_reg.  It's 
known in find_reg, but it's not passed back out.  It could be rediscovered 
by a second scan of the register array, though, to match the REG pointer.

Even when passing a register index and unit pointer, or a register pointer, 
there's still the problem of identifying how that register is to be handled 
within fprint_sym.  I think that something within the REG structure itself 
needs to be the identifier, as identifying via the index or REG address 
leads to maintenance issues, as I've noted earlier.

As an aside, I've not looked carefully, but I suspect that the 
sim_vm_parse_addr and sim_vm_fprint_addr routines are just special cases of 
this more general problem of knowing which register is being passed so that 
you then know how to handle its parsing or printing.  It'd be nice if a 
general solution could be found that would fold these in as well.

                                      -- Dave