Add a helper function to trad_frame to support register cache maps.

Currently, signal frame handlers require explicitly coded calls to
trad_frame_set_reg_addr() to describe the location of saved registers
within a signal frame.  This change permits the regcache_map_entry
arrays used with regcache::supply_regset and regcache::collect_regset
to be used to describe a block of saved registers given an initial
address for the register block.

Some systems use the same layout for registers in core dump notes,
native register sets with ptrace(), and the register contexts saved in
signal frames.  On these systems, a single register map can now be
used to describe the layout of registers in all three places.

If a register map entry's size does not match the native size of a
register, try to match the semantics used by
regcache::transfer_regset.  If a register slot is too large, assume
that the register's value is stored in the first N bytes and ignore
the remaning bytes.  If the register slot is smaller than the
register, assume the slot holds the low N bytes of the register's
value.  Read these low N bytes from the target and zero-extend them to
generate a register value.

While here, document the semantics for both regcache::transfer_regset
and trad_frame with respect to register slot's whose size does not
match the register's size.

gdb/ChangeLog:

	* regcache.h (struct regcache_map_entry): Note that this type can
	be used with traditional frame caches.
	* trad-frame.c (trad_frame_set_reg_regmap): New.
	* trad-frame.h (trad_frame_set_reg_regmap): New.

1 files changed, 4 insertions, 0 deletions

diff --git a/gdb/trad-frame.h b/gdb/trad-frame.h
index a11a2c2..0d04bf4 100644
--- a/gdb/trad-frame.h
+++ b/gdb/trad-frame.h
@@ -23,6 +23,7 @@
 #include "frame.h"		/* For "struct frame_id".  */
 
 struct frame_info;
+struct regcache_map_entry;
 struct trad_frame_cache;
 
 /* A simple, or traditional frame cache.
@@ -45,6 +46,9 @@ void trad_frame_set_reg_realreg (struct trad_frame_cache *this_trad_cache,
 				 int regnum, int realreg);
 void trad_frame_set_reg_addr (struct trad_frame_cache *this_trad_cache,
 			      int regnum, CORE_ADDR addr);
+void trad_frame_set_reg_regmap (struct trad_frame_cache *this_trad_cache,
+				const struct regcache_map_entry *regmap,
+				CORE_ADDR addr, size_t size);
 void trad_frame_set_reg_value (struct trad_frame_cache *this_cache,
 			       int regnum, LONGEST val);