Re: [PATCH/i386newframe/RFC] DWARF CFI frame unwinder

[Mark Kettenis <kettenis@chello.nl>]

   Date: Sun, 04 May 2003 23:35:27 -0400
   From: Andrew Cagney <ac131313@redhat.com>

   Mark, fyi,

   > +    case REG_SAVED_REG:
   > +      *optimizedp = 0;
   > +      *lvalp = lval_register;
   > +      *addrp = 0;
   > +      *realnump = DWARF2_REG_TO_REGNUM (cache->reg[regnum].loc.reg);
   > +      if (valuep)
   > +	{
   > +	  /* Read the value from the register.  */
   > +	  frame_unwind_register (next_frame, *realnump, valuep);
   > +	}
   > +      break;
   > +

   Set *addrp to the register offset hack (Otherwize something mysterious 
   fails.  What? I don't remember).

Yes, findvar.c:value_of_register() and findvar.c:value_from_register()
use this.  Worse, our whole value subsystem seems to rely on this.
Ughh, that's really gross.  We should do something about that!

Anyway.  Thinking about it a bit more, I suspect the whole handling of
REG_SAVED_REG is wrong.  Instead, we should just change the register
number according to the DWARF CFI rule and let the unwinder for
NEXT_FRAME handle the request:

    case REG_SAVED_REG:
      regnum = DWARF2_REG_TO_REGNUM (cache->reg[regnum].loc.reg);
      /* FALLTHROUGH */

    case REG_UNMODIFIED:
      frame_register_unwind (next_frame, regnum,
			     optimizedp, lvalp, addrp, realnump, valuep);
      break;

Eventually this means that sentinel_frame_prev_register will provide
the register offset hack.

Do you agree with my analysis?

Mark