Saving/restoring the entire register set

[Richard Earnshaw <rearnsha@arm.com>]

The current implementation of generic_{push,pop}_dummy_frame use 

	{read,write}_register_bytes (0, addr, REGISTER_BYTES)

to save/restore the entire regset.  

This is causing a problem for me with the new pseudo/raw register
separation that I'm trying to create because write_register_bytes calls
write_register_gen which calls arm_register_write and then aborts because
we are trying to directly update a raw register rather than a pseudo.

While the dummy frame code does seem to be doing something sensible, doing
it this way is somewhat of a pain, because I really want to fault out
attempts to directly poke into the raw registers (I've already tracked down
two or three bugs this way).

For this special case of saving/restoring the entire register bank, I wonder if a more suitable interface might be to have calls such as

  struct regcache *regcache_alloc (); /* Allocate a new regcache structure */
  regcache_save (regcache);	      /* Copy current registers into it */
  regcache_restore (regcache);	      /* Restore registers from it */
  regcache_free (regcache);	      /* Release it */

which would directly perform the precise operations that are required.

These routines could then directly use the legacy_{read,write}_register_gen
interface to fill/restore a copy of the structure. 

R.