perf top: Don't stop if no kernel symtab is found

We now just warn the user about the fact and go on providing just
userspace samples.

This fixes a problem when no vmlinux is explicetely passed by the user,
thus symbol_conf.vmlinux_name is NULL, no suitable vmlinux is found, and
then we get:

 aldebaran:~> perf top -p 7557
 [kernel.kallsyms] with build id 44d9a989eabbd79e486bc079d6b743d397c204e0
 not found, continuing without symbols
 The (null) file can't be used
Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Link: http://lkml.kernel.org/n/tip-cj2g81hn64wv2bipmqk4fy2m@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -81,6 +81,7 @@ static bool			use_tui, use_stdio;
 static int			default_interval		=      0;
 
 static bool			kptr_restrict_warned;
+static bool			vmlinux_warned;
 static bool			inherit				=  false;
 static int			realtime_prio			=      0;
 static bool			group				=  false;
@@ -754,6 +755,7 @@ static void perf_event__process_sample(const union perf_event *event,
 	}
 
 	if (al.sym == NULL) {
+		const char *msg = "Kernel samples will not be resolved.\n";
 		/*
 		 * As we do lazy loading of symtabs we only will know if the
 		 * specified vmlinux file is invalid when we actually have a
@@ -765,12 +767,20 @@ static void perf_event__process_sample(const union perf_event *event,
 		 * --hide-kernel-symbols, even if the user specifies an
 		 * invalid --vmlinux ;-)
 		 */
-		if (al.map == machine->vmlinux_maps[MAP__FUNCTION] &&
+		if (!kptr_restrict_warned && !vmlinux_warned &&
+		    al.map == machine->vmlinux_maps[MAP__FUNCTION] &&
 		    RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION])) {
-			ui__warning("The %s file can't be used\n",
-				    symbol_conf.vmlinux_name);
-			exit_browser(0);
-			exit(1);
+			if (symbol_conf.vmlinux_name) {
+				ui__warning("The %s file can't be used.\n%s",
+					    symbol_conf.vmlinux_name, msg);
+			} else {
+				ui__warning("A vmlinux file was not found.\n%s",
+					    msg);
+			}
+
+			if (use_browser <= 0)
+				sleep(5);
+			vmlinux_warned = true;
 		}
 
 		return;