scripts/gdb: provide exception catching parser

If we attempt to read a value that is not available to GDB, an exception
is raised.  Most of the time, this is a good thing; however on occasion
we will want to be able to determine if a symbol is available.

By catching the exception to simply return None, we can determine if we
tried to read an invalid value, without the exception taking our
execution context away from us

Link: http://lkml.kernel.org/r/c72b25c06fc66e1d68371154097e2cbb112555d8.1462865983.git.jan.kiszka@siemens.com
Signed-off-by: Kieran Bingham <kieran.bingham@linaro.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/gdb/linux/utils.py

@@ -154,3 +154,10 @@ def get_gdbserver_type():
         if gdbserver_type is not None and hasattr(gdb, 'events'):
             gdb.events.exited.connect(exit_handler)
     return gdbserver_type
+
+
+def gdb_eval_or_none(expresssion):
+    try:
+        return gdb.parse_and_eval(expresssion)
+    except:
+        return None