[WIP/RFC] MIPS registers overhaul

[Kevin Buettner]

On May 21,  3:15pm, Andrew Cagney wrote:

> > On May 21, 12:58pm, Daniel Jacobowitz wrote:
> > 
> >> > From GDB's view point, the ISA is 64 bit.
> >> > 
> >> > The fact that a specific remote debug agent choses to use 32 bit 
> >> > registers is a limitation of that debug agent / kernel.  An embedded 
> >> > target, and I'm pretty sure IRIX 6.5, for instance, don't do that.
> > 
> >> 
> >> No, from GDB's view point in this situation, the target ISA is _NOT_ 64
> >> bit.  Nothing 64-bit is available, either to the inferior or to the
> >> debugger.  Period.
> >> 
> >> I would be a little surprised if IRIX didn't work that way too, but I
> >> don't have access to IRIX to poke around.
> > 
> > 
> > I too would be surprised.  I should think that SGI would want to
> > ensure that legacy programs (i.e, those using the o32 ABI) behave the
> > same when run on 64-bit hardware as they do when run on 32-bit
> > hardware.  One of the implications of this is that illegal
> > instructions in the 32-bit ISA should continue to be illegal when run
> > on the 64-bit hardware.
> 
> Er, it's the same deal as for SPARC.  If GDB is built against the 64 bit 
> debug interface, it can debug both 32 and 64 bit applications.  This is 
> the debuggers view, not the program being run's view.

Well, sure.  But for such applications, you don't lose anything by
permitting GDB to view it as a 32-bit application only.  I.e, there's
nothing that the application is going to do for which there will be a
benefit to have a 64-bit view of it from the outside.

Kevin