extern int gdbarch_sdb_reg_to_regnum (struct gdbarch *gdbarch, int sdb_regnr);
extern void set_gdbarch_sdb_reg_to_regnum (struct gdbarch *gdbarch, gdbarch_sdb_reg_to_regnum_ftype *sdb_reg_to_regnum);
-/* Provide a default mapping from a DWARF2 register number to a gdb REGNUM. */
+/* Provide a default mapping from a DWARF2 register number to a gdb REGNUM.
+ Return -1 for bad REGNUM. Note: Several targets get this wrong. */
typedef int (gdbarch_dwarf2_reg_to_regnum_ftype) (struct gdbarch *gdbarch, int dwarf2_regnr);
extern int gdbarch_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int dwarf2_regnr);