Re: mips-tdep.c: Adjust breakpoints in branch delay slots

[Daniel Jacobowitz <drow@false.org>]

On Fri, May 25, 2007 at 01:21:57PM +0100, Maciej W. Rozycki wrote:
> On Fri, 25 May 2007, Maciej W. Rozycki wrote:
> 
> >  In principle on bare iron it should be doable, but the problem is, IIRC, 
> > the state of cp0.cause.bd is not propagated under Linux to userland in any 
> > way.  And at the moment I'm not sure how this would affect EJTAG debugging 
> > either.
> 
>  FYI, I have now checked Linux and it should be fine -- must have been my 
> bad memory.  EJTAG has provisions for handling this correctly 
> (cp0.debug.dbd), but I'm not sure if associated software gets it right.

Great.  Want to take a look at doing this the other way then?

The best option I can think of would be to fake the PC value based on
the value of BD.  You might be able to do this cleverly; have a
register named "$pc" which shows the hardware contents of the PC
register, and have read_pc / unwind_pc / write_pc adjust based on BD.
I'm not sure if that will work, but it does mimic the architecture
behavior, which is an encouraging sign; and some other platforms do
similar magic (e.g. HP/UX and IA64).

It might be best to eliminate the setting of PC_REGNUM first, but
that's multi-arch work; I see that dwarf2-frame.c relies on it unless
you set dwarf2_frame_default_init_reg.

-- 
Daniel Jacobowitz
CodeSourcery