ktest: Fix config bisect with how make oldnoconfig works

With a name like 'oldnoconfig' one may think that the config generated
would disable all configs that were not defined (selecting "no" for all
options). But this is not the case. It selects the default. If a config
has a 'default y', then it is added if not specified.

This broke the config bisect, because options not specified by a config
will just use the default, where it expected to turn off. This caused an
option to be enabled that disabled an option that would break the build.
The end result was that we never found the bad config at the end of the
test.

Instead of using 'make oldnoconfig', ktest now builds the options it
expects enabled and disabled. When it turns off an option, it will no
longer remove it, but actually set it to:

 # CONFIG_FOO is not set.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -189,6 +189,9 @@
 my %entered_configs;
 my %config_help;
 my %variable;
+
+# force_config is the list of configs that we force enabled (or disabled)
+# in a .config file. The MIN_CONFIG and ADD_CONFIG configs.
 my %force_config;
 
 # do not force reboots on config problems
@@ -1837,6 +1840,7 @@ sub make_oldconfig {
 sub load_force_config {
     my ($config) = @_;
 
+    doprint "Loading force configs from $config\n";
     open(IN, $config) or
 	dodie "failed to read $config";
     while (<IN>) {
@@ -2389,9 +2393,24 @@ sub bisect {
     success $i;
 }
 
+# config_ignore holds the configs that were set (or unset) for
+# a good config and we will ignore these configs for the rest
+# of a config bisect. These configs stay as they were.
 my %config_ignore;
+
+# config_set holds what all configs were set as.
 my %config_set;
 
+# config_off holds the set of configs that the bad config had disabled.
+# We need to record them and set them in the .config when running
+# oldnoconfig, because oldnoconfig does not turn off new symbols, but
+# instead just keeps the defaults.
+my %config_off;
+
+# config_off_tmp holds a set of configs to turn off for now
+my @config_off_tmp;
+
+# config_list is the set of configs that are being tested
 my %config_list;
 my %null_config;
 
@@ -2470,6 +2489,16 @@ sub create_config {
 	}
     }
 
+    # turn off configs to keep off
+    foreach my $config (keys %config_off) {
+	print OUT "# $config is not set\n";
+    }
+
+    # turn off configs that should be off for now
+    foreach my $config (@config_off_tmp) {
+	print OUT "# $config is not set\n";
+    }
+
     foreach my $config (keys %config_ignore) {
 	print OUT "$config_ignore{$config}\n";
     }
@@ -2551,6 +2580,13 @@ sub run_config_bisect {
     do {
 	my @tophalf = @start_list[0 .. $half];
 
+	# keep the bottom half off
+	if ($half < $#start_list) {
+	    @config_off_tmp = @start_list[$half + 1 .. $#start_list];
+	} else {
+	    @config_off_tmp = ();
+	}
+
 	create_config @tophalf;
 	read_current_config \%current_config;
 
@@ -2567,7 +2603,11 @@ sub run_config_bisect {
 	if (!$found) {
 	    # try the other half
 	    doprint "Top half produced no set configs, trying bottom half\n";
+
+	    # keep the top half off
+	    @config_off_tmp = @tophalf;
 	    @tophalf = @start_list[$half + 1 .. $#start_list];
+
 	    create_config @tophalf;
 	    read_current_config \%current_config;
 	    foreach my $config (@tophalf) {
@@ -2705,6 +2745,10 @@ sub config_bisect {
 		$added_configs{$2} = $1;
 		$config_list{$2} = $1;
 	    }
+	} elsif (/^# ((CONFIG\S*).*)/) {
+	    # Keep these configs disabled
+	    $config_set{$2} = $1;
+	    $config_off{$2} = $1;
 	}
     }
     close(IN);
@@ -2727,6 +2771,8 @@ sub config_bisect {
     my %config_test;
     my $once = 0;
 
+    @config_off_tmp = ();
+
     # Sometimes kconfig does weird things. We must make sure
     # that the config we autocreate has everything we need
     # to test, otherwise we may miss testing configs, or