[linuxsh-dev] Re: Question : GBD Stub to boot a machine.

[Jeremy S. <js...@mv...>]

Fabio Giovagnini wrote:

> Hi, every body,
> I'm woking on porting linux-sh on a my own sh-3 based board.
> To debug the software regarding the machvect description, I boot my card
> using sh-ilp+g and everything works good.
> Now I'd like to put on the flash of another my development sh-2 based card
> the gdbstub I found on sourceforge to achieve the following target:
> 1) power up my card;
> 2) load on ram my program;
> 3) execute from ram my  program;
> 4) debug it.
>
> Some doubts:
> 1) How do I have to link my application program I like to debug using gdbstub?
> 2) Is it possible to use gdbstub to debug a loaded program (using (gdb) load
> /root/myrog command); or gdbstub has to be a part of my application program?
> 3) Can I try to compile sh-ipl+g for may sh-7044 based card, or it has too
> much specific part sh-3 and sh-4 related?

Here's my take on it:

1) I don't think it matters how you link it, as long as it knows where it wants
to be in RAM.
2) You can load w/gdb as long as you're talking to an independent stub.  The stub
and app have to agree on (a) serial port usage, and (b) exception handling; this
is necessary whether the app and stub are linked together or not.
3) There's the rub: I've not used the SH2, but from what little I know it's
very different than the SH3/4 in terms of exception handling and register set.
Not only would you need to write the BSC init for your board (like any port) but
you'd need to rewrite entry.S to deal with the fact that exception vectors are
addresses rather than code blocks, there are no bank registers, etc; the stub
itself my need to change the register handling if the stacked register set looks
different (but that also depends heavily on what the gdb the stub is talking to
expects).  Even the serial ports (if available) may be different, requiring work
in sh-sci.c too...

The upshot is that I don't think the SH3/4 version will "drop in" easily.  (But
there might be an SH2 version floating around... in fact, I think if you look at
the GDB package there might be some sample stubs there, and the SH one might be a
good SH2 starting point for linking with your app?)

Good luck,
  --Jeremy Siegel