[rfc] dwarf2 unwinder and MIPS n32

[Daniel Jacobowitz <drow@false.org>]

The DWARF-2 unwinder uses store_typed_address to store the value of
the CFA or RA into a register-sized buffer.  The type of the register
might be a pointer or integer type, so it passes
builtin_type_void_data_ptr and builtin_type_void_func_ptr as
appropriate.  But for MIPS N32, sizeof (void *) == 4 and the stack
pointer is 64-bit.  So it unwinds writes four bytes into the first
four of the eight byte slot; since I'm testing big-endian, the failure
is quickly obvious.

So what do we do about it?  The patch below works for MIPS, but I'm
reasonably sure it's wrong; it avoids the architecture's
ADDRESS_TO_POINTER method entirely.  If we pass the register's type to
store_typed_address we'll get various failures if the architecture
doesn't define the relevant register as a pointer.  And MIPS doesn't,
partly because the register is 64-bit and the pointer would only be
32-bit.

Maybe if the size of the register != the size of a void * we should
store it as an unsigned integer.  But that seems hackish to me.

I'd love comments; I don't want to commit this patch, but I can't turn
on CFI for MIPS without it.

-- 
Daniel Jacobowitz
CodeSourcery

2007-04-28  Daniel Jacobowitz  <dan@codesourcery.com>

	* dwarf2-frame.c (dwarf2_frame_prev_register): Use
	store_unsigned_integer instead of store_typed_address.

---
 dwarf2-frame.c |   15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

Index: gdb/dwarf2-frame.c
===================================================================
--- gdb.orig/dwarf2-frame.c	2007-04-27 17:03:21.000000000 -0400
+++ gdb/dwarf2-frame.c	2007-04-27 17:42:37.000000000 -0400
@@ -1137,10 +1137,8 @@ dwarf2_frame_prev_register (struct frame
       *addrp = 0;
       *realnump = -1;
       if (valuep)
-	{
-	  /* Store the value.  */
-	  store_typed_address (valuep, builtin_type_void_data_ptr, cache->cfa);
-	}
+	store_unsigned_integer (valuep, register_size (gdbarch, regnum),
+				cache->cfa);
       break;
 
     case DWARF2_FRAME_REG_CFA_OFFSET:
@@ -1149,11 +1147,8 @@ dwarf2_frame_prev_register (struct frame
       *addrp = 0;
       *realnump = -1;
       if (valuep)
-	{
-	  /* Store the value.  */
-	  store_typed_address (valuep, builtin_type_void_data_ptr,
-			       cache->cfa + cache->reg[regnum].loc.offset);
-	}
+	store_unsigned_integer (valuep, register_size (gdbarch, regnum),
+				cache->cfa + cache->reg[regnum].loc.offset);
       break;
 
     case DWARF2_FRAME_REG_RA_OFFSET:
@@ -1167,7 +1162,7 @@ dwarf2_frame_prev_register (struct frame
 
           regnum = DWARF2_REG_TO_REGNUM (cache->retaddr_reg.loc.reg);
           pc += frame_unwind_register_unsigned (next_frame, regnum);
-          store_typed_address (valuep, builtin_type_void_func_ptr, pc);
+	  store_unsigned_integer (valuep, register_size (gdbarch, regnum), pc);
         }
       break;