s390: have unique symbol for __switch_to address

After linking there are several symbols for the same address that the
__switch_to symbol points to. E.g.:

000000000089b9c0 T __kprobes_text_start
000000000089b9c0 T __lock_text_end
000000000089b9c0 T __lock_text_start
000000000089b9c0 T __sched_text_end
000000000089b9c0 T __switch_to

When disassembling with "objdump -d" this results in a missing
__switch_to function. It would be named __kprobes_text_start
instead. To unconfuse objdump add a nop in front of the kprobes text
section. That way __switch_to appears again.

Obviously this solution is sort of a hack, since it also depends on
link order if this works or not. However it is the best I can come up
with for now.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -163,6 +163,16 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	.endm
 
 	.section .kprobes.text, "ax"
+.Ldummy:
+	/*
+	 * This nop exists only in order to avoid that __switch_to starts at
+	 * the beginning of the kprobes text section. In that case we would
+	 * have several symbols at the same address. E.g. objdump would take
+	 * an arbitrary symbol name when disassembling this code.
+	 * With the added nop in between the __switch_to symbol is unique
+	 * again.
+	 */
+	nop	0
 
 /*
  * Scheduler resume function, called by switch_to