[PATCH 18/18] [DO NOT MERGE] Makefile: enable switch/case fallthrough warnings

[Andre Przywara]

=================================================================
This does not fully work yet, there is at least the libbz2 code
left to be handled. But this patch helps to let CI find more
places where we need annotations.
=================================================================

C's implicit fallthrough behaviour in switch/case statements can lead to
subtle bugs. Quite some while ago many compilers introduced warnings in
those cases, requiring intentional fallthrough's to be annotated.

So far we were not enabling that compiler option, so many ambiguities
and some bugs in the code went unnoticed.

With all places that produced warnings fixed or annotated now, we can
add this compiler option to the build flags, to find new ambiguities
early, before the code gets merged.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index 7d83ce16721..46c48556788 100644
--- a/Makefile
+++ b/Makefile
@@ -808,6 +808,7 @@ endif
 # These warnings generated too much noise in a regular build.
 # Use make W=1 to enable them (see scripts/Makefile.extrawarn)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+KBUILD_CFLAGS += -Wimplicit-fallthrough
 
 # Prohibit date/time macros, which would make the build non-deterministic
 KBUILD_CFLAGS   += $(call cc-option,-Werror=date-time)
-- 
2.25.1