Register fudging (CRISv32)

[Orjan Friberg <orjan.friberg@axis.com>]

My upcoming CRISv32 port (remote target, Linux based) is starting to 
look pretty good(*) but I'm left with a nagging feeling that the 
register fudging I'm doing isn't necessarily done where it should be 
and/or the right way.  Right now it's being done in three different 
places (this relating to debugging user-mode programs):

(1) in the kernel
(2) in the Gdbserver
(3) in GDB

Basically, what I would like to hear is people's opinions on how various 
kinds of register fudging should be done.

On to the details:

* The first fudging is the equivalent to DECR_PC_AFTER_BREAK, though 
it's not using that mechanism in GDB; instead it's being done in the 
kernel.  On one hand I feel more comfortable doing it in the kernel 
where I know exactly what happens; on the other hand the decrementation 
needs to be duplicated in, for example, a classic kernel gdb stub. 
Should I be using DECR_PC_AFTER_BREAK in GDB instead?  Or the 
implementation in the Gdbserver?

* Another fudging that takes place is the filling in of a pseudo-PC 
register (there is no actual PC register, so it's not present in struct 
pt_regs).  This is being done in the Gdbserver.  In addition, in case we 
stopped in a delay slot, I *may* need to look at the code to determine 
what the PC should be set to (meaning I can't rely on register contents 
alone).  I've found 3 cases where this needs to be done:

   (1) In case of a stop (break, h/w watchpoint, receiving a signal etc)
   (2) When unwinding a sigtramp frame
   (3) When loading a core dump (supply_gregset)

As of now, delay-slot-adjustment of the PC is only being done for the 
first case (normal stop), and it's also done in the Gdbserver.  The 
other two cases don't handle being stopped in a delay slot yet, though I 
have a hunch this could be done in GDB.

* In addition to this, I need to set the h/w single-step PC to 0 in the 
kernel at various times, but I've seen other architectures doing that 
and I feel pretty confident that is the right way to do it.

Thanks for any insights.


(*) the gdb.base testsuite results in about 6050 PASS and around 20 FAIL 
(the relatively new sigbpt.exp, siginfo.exp, signull.exp, and 
sigstep.exp are all PASS - yay!)

-- 
Orjan Friberg
Axis Communications