leaking_addresses: add support for kernel config file

Features that rely on the ability to get kernel configuration options
are ready to be implemented in script. In preparation for this we can
add support for kernel config options as a separate patch to ease
review.

Add support for locating and parsing kernel configuration file.
Signed-off-by: Tobin C. Harding <me@tobin.cc>

scripts/leaking_addresses.pl

@@ -41,10 +41,10 @@ my $debug = 0;
 my $raw = 0;
 my $output_raw = "";	# Write raw results to file.
 my $input_raw = "";	# Read raw results from file instead of scanning.
-
 my $suppress_dmesg = 0;		# Don't show dmesg in output.
 my $squash_by_path = 0;		# Summary report grouped by absolute path.
 my $squash_by_filename = 0;	# Summary report grouped by filename.
+my $kernel_config_file = "";	# Kernel configuration file.
 
 # Do not parse these files (absolute path).
 my @skip_parse_files_abs = ('/proc/kmsg',
@@ -99,6 +99,7 @@ Options:
 	      --suppress-dmesg		Do not show dmesg results.
 	      --squash-by-path		Show one result per unique path.
 	      --squash-by-filename	Show one result per unique filename.
+	--kernel-config-file=<file>     Kernel configuration file (e.g /boot/config)
 	-d, --debug			Display debugging output.
 	-h, --help, --version		Display this help and exit.
 
@@ -118,6 +119,7 @@ GetOptions(
 	'squash-by-path'        => \$squash_by_path,
 	'squash-by-filename'    => \$squash_by_filename,
 	'raw'                   => \$raw,
+	'kernel-config-file=s'	=> \$kernel_config_file,
 ) or help(1);
 
 help(0) if ($help);
@@ -187,6 +189,68 @@ sub is_ppc64
 	return 0;
 }
 
+# Gets config option value from kernel config file.
+# Returns "" on error or if config option not found.
+sub get_kernel_config_option
+{
+	my ($option) = @_;
+	my $value = "";
+	my $tmp_file = "";
+	my @config_files;
+
+	# Allow --kernel-config-file to override.
+	if ($kernel_config_file ne "") {
+		@config_files = ($kernel_config_file);
+	} elsif (-R "/proc/config.gz") {
+		my $tmp_file = "/tmp/tmpkconf";
+
+		if (system("gunzip < /proc/config.gz > $tmp_file")) {
+			dprint "$0: system(gunzip < /proc/config.gz) failed\n";
+			return "";
+		} else {
+			@config_files = ($tmp_file);
+		}
+	} else {
+		my $file = '/boot/config-' . `uname -r`;
+		chomp $file;
+		@config_files = ($file, '/boot/config');
+	}
+
+	foreach my $file (@config_files) {
+		dprint("parsing config file: %s\n", $file);
+		$value = option_from_file($option, $file);
+		if ($value ne "") {
+			last;
+		}
+	}
+
+	if ($tmp_file ne "") {
+		system("rm -f $tmp_file");
+	}
+
+	return $value;
+}
+
+# Parses $file and returns kernel configuration option value.
+sub option_from_file
+{
+	my ($option, $file) = @_;
+	my $str = "";
+	my $val = "";
+
+	open(my $fh, "<", $file) or return "";
+	while (my $line = <$fh> ) {
+		if ($line =~ /^$option/) {
+			($str, $val) = split /=/, $line;
+			chomp $val;
+			last;
+		}
+	}
+
+	close $fh;
+	return $val;
+}
+
 sub is_false_positive
 {
 	my ($match) = @_;