kunit: tool: revamp message for invalid kunitconfig

The current error message is precise, but not very clear if you don't
already know what it's talking about, e.g.

> $ make ARCH=um olddefconfig O=.kunit
> ERROR:root:Provided Kconfig is not contained in validated .config. Following fields found in kunitconfig, but not in .config: CONFIG_DRM=y

Try to reword the error message so that it's
* your missing options usually have unsatisified dependencies
* if you're on UML, that might be the cause (it is, in this example)
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/kunit/kunit_kernel.py

@@ -266,15 +266,17 @@ class LinuxSourceTree(object):
 	def validate_config(self, build_dir) -> bool:
 		kconfig_path = get_kconfig_path(build_dir)
 		validated_kconfig = kunit_config.parse_file(kconfig_path)
-		if not self._kconfig.is_subset_of(validated_kconfig):
-			invalid = self._kconfig.entries() - validated_kconfig.entries()
-			message = 'Provided Kconfig is not contained in validated .config. Following fields found in kunitconfig, ' \
-					  'but not in .config: %s' % (
-					', '.join([str(e) for e in invalid])
-			)
-			logging.error(message)
-			return False
-		return True
+		if self._kconfig.is_subset_of(validated_kconfig):
+			return True
+		invalid = self._kconfig.entries() - validated_kconfig.entries()
+		message = 'Not all Kconfig options selected in kunitconfig were in the generated .config.\n' \
+			  'This is probably due to unsatisfied dependencies.\n' \
+			  'Missing: ' + ', '.join([str(e) for e in invalid])
+		if self._arch == 'um':
+			message += '\nNote: many Kconfig options aren\'t available on UML. You can try running ' \
+				   'on a different architecture with something like "--arch=x86_64".'
+		logging.error(message)
+		return False
 
 	def build_config(self, build_dir, make_options) -> bool:
 		kconfig_path = get_kconfig_path(build_dir)