tracing/kprobes: Fix probe offset to be unsigned

Prohibit user to specify negative offset from symbols.
Since kprobe.offset is unsigned int, the offset must be always positive
value.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jason Baron <jbaron@redhat.com>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <20090910235314.22412.64631.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index 3de7517..db55318 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -25,15 +25,15 @@
 
 Synopsis of kprobe_events
 -------------------------
-  p[:EVENT] SYMBOL[+offs|-offs]|MEMADDR [FETCHARGS]	: Set a probe
-  r[:EVENT] SYMBOL[+0] [FETCHARGS]			: Set a return probe
+  p[:EVENT] SYMBOL[+offs]|MEMADDR [FETCHARGS]	: Set a probe
+  r[:EVENT] SYMBOL[+0] [FETCHARGS]		: Set a return probe
 
- EVENT			: Event name. If omitted, the event name is generated
-			  based on SYMBOL+offs or MEMADDR.
- SYMBOL[+offs|-offs]	: Symbol+offset where the probe is inserted.
- MEMADDR		: Address where the probe is inserted.
+ EVENT		: Event name. If omitted, the event name is generated
+		  based on SYMBOL+offs or MEMADDR.
+ SYMBOL[+offs]	: Symbol+offset where the probe is inserted.
+ MEMADDR	: Address where the probe is inserted.
 
- FETCHARGS		: Arguments. Each probe can have up to 128 args.
+ FETCHARGS	: Arguments. Each probe can have up to 128 args.
   %REG	: Fetch register REG
   sN	: Fetch Nth entry of stack (N >= 0)
   sa	: Fetch stack address.