Dwarf-2 unwinding vs. manual prologue analysis

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

When adding the CRISv32 support, it seemed like a good idea to avoid having to 
do manual prologue analysis to determine where registers are saved, figuring out 
the return address etc.  For some reason I imagined I wouldn't have to do this 
if I could use the Dwarf-2 frame sniffer (because all code would have Dwarf-2 
CFI).  I hooked in the Dwarf-2 frame sniffer and everything ran fine, and it 
wasn't until just recently that I discovered (to my horror) that the prologue 
scanner (meant for CRISv10 only; the ISAs are not compatible) was not only 
called when debugging CRISv32, but simple things like 'next' broke in various 
places in the testsuite when I didn't do it.

I do feel a bit embarrased asking this, as one would think I'd know this 
already.  Since I obviously don't, here we go:

Do I need to able to do manual prologue analysis when there's Dwarf-2 CFI 
available?  If so, is there a set of minimum requirements for what that analysis 
must be able figure out?


For the record: I created a minimal prologue scanner for CRISv32 by using the 
time-honoured method of gradually stripping away stuff from the CRISv10 version 
until things stopped working.  This is what I ended up with:

   frame_unwind_unsigned_register (next_frame, SP_REGNUM, &this_base);
   info->base = this_base;
   info->prev_sp = this_base;

   /* The PC is found in SRP (the actual register or located on the stack).  */
   info->saved_regs[PC_REGNUM] = info->saved_regs[SRP_REGNUM];


-- 
Orjan Friberg
Axis Communications