register type as signed or unsigned?

[ligang@sunnorth.com.cn]

hello all,

I am porting GDB to a new target.
I am not aware of the meaning of register type.
You can do as follows:
set_gdbarch_register_type (gdbarch, builtin_type_int32);
or
set_gdbarch_register_type (gdbarch, builtin_type_uint32);

What is the real difference between the two situation?
Why should GDB specify the register type as signed or unsigned?
Dose it mean the former must use regcache_cooked_read_signed() and the 
latter must use
regcache_cooked_read_unsigned()?

Best regards
                     Ligang