Re: SH5 simulator contribution

[Andrew Cagney <ac131313 at cygnus dot com>]

> Andrew Cagney wrote:
> 
>> The sim/sh simulator has a specific register name / number / size 
>> mapping and sh-elf-gdb knows how to use it.
>> 
>> This new sim/sh5 simulator has a different register / name / size 
>> mapping and this difference is covered up by GDB.  (I note the addition 
>> of the sim-sh64.h file which is in itself a very good move).
> 
> 
> Actually, the difference is not covered up by gdb.  The compiler emits
> different register numbers when compiling for sh5 or shcompact than
> when compiling for sh1..sh4.
> The sh64 simulator matches the numbering scheme for the sh5 / shcompact
> targets, while the old sh simulator matches the numbering scheme for
> sh1..sh4 targets.  When you try to use gdb with the sh64 simulator
> as submitted so far on an sh4 program (i.e. set a breakpoint, display
> registers), it just falls over.

Until the sim works, GDB probably won't add the code :-)  The 
infrastructure is there.

> In order to have a unified interface between gdb and the simulator, you
> would have first to introduce a translation step in gdb to translate the
> old register numbers for sh1..sh4 programs to the new scheme, and in the
> old simulator translate it back (the latter is easy, since there is
> already a translation going on in sim_store_register / sim_fetch_register).


> You can't just change the numbering in the interface between gcc and gdb,
> because that would break binary compatibility.  And you also can't change
> the interface between gdb and hardware monitors.

Strictly speaking GCC does re-number the interface between GCC and GDB. 
  .stabs and dwarf2 debug info can have different register numbering for 
the same ISA/ABI.  Fortunatly GDB has mechanisms for handling this.

As for hardware monitors, I'm not sure.  I do know that the MIPS has 
more G packet formats than I've had hot dinners.  Here, unfortunatly, 
the mechanisms GDB needed to handle this are still work-in-progress.

As for the SIM, there is REGISTER_SIM_REGNO.  However, that may not be 
sufficient.

> So I don't see that you gain anything by unifying the numbering scheme
> in the gdb <-> sim interface, as it would be at odds with the interface
> to gcc and the hardware interfaces.

Formalizing would be a better word.  So that GDB and the SIM can agree 
on the register numbers and their sizes without needing to know the 
others internals.

Andrew