I stay in some objc code and want to step.
In gdb 6.3.1 it is possible to step, but there are unwanted
steps such as:
(gdb) s
objc_msg_lookup_super (super=0x22f4b8, sel=0x13978c8) at sendmsg.c:215
215       if (super->self)
Current language:  auto; currently c
(gdb) n
216         return get_imp (super->class, sel);
(gdb) n
get_imp (class=0x13957e0, sel=0x13978c8) at sendmsg.c:113
113     {
(gdb) n

In gdb 6.0 I can step directly to objc-message code.