perf report: Fix --no-call-chain option handling

To avoid the funny:

 [root@doppio ~]# perf record -a -f sleep 2s
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.334 MB perf.data (~14572 samples) ]
 [root@doppio ~]# perf report --no-call-graph
 selected -g but no callchain data. Did you call perf record without -g?

And fix the bug reported by peterz when we do indeed record with
callchains and then ask for a report without:

[root@doppio ~]# perf record -a -g -f sleep 2s
[root@doppio ~]# perf report --no-call-graph
Segmentation fault
[root@doppio ~]#

Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1262699685-27820-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-report.c

@@ -35,6 +35,7 @@ static char		const *input_name = "perf.data";
 
 static int		force;
 static bool		hide_unresolved;
+static bool		dont_use_callchains;
 
 static int		show_threads;
 static struct perf_read_values	show_threads_values;
@@ -172,7 +173,8 @@ static int perf_session__setup_sample_type(struct perf_session *self)
 					" -g?\n");
 			return -1;
 		}
-	} else if (callchain_param.mode != CHAIN_NONE && !symbol_conf.use_callchain) {
+	} else if (!dont_use_callchains && callchain_param.mode != CHAIN_NONE &&
+		   !symbol_conf.use_callchain) {
 			symbol_conf.use_callchain = true;
 			if (register_callchain_param(&callchain_param) < 0) {
 				fprintf(stderr, "Can't register callchain"
@@ -246,11 +248,19 @@ static int __cmd_report(void)
 
 static int
 parse_callchain_opt(const struct option *opt __used, const char *arg,
-		    int unset __used)
+		    int unset)
 {
 	char *tok;
 	char *endptr;
 
+	/*
+	 * --no-call-graph
+	 */
+	if (unset) {
+		dont_use_callchains = true;
+		return 0;
+	}
+
 	symbol_conf.use_callchain = true;
 
 	if (!arg)