@@ -573,6 +573,15 @@ virt-y := virt/
endif # KBUILD_EXTMOD
ifeq ($(dot-config),1)
+# Require a 'make clean' if the compiler changed; not only does the .cache.mk
+# need to be thrown out but we should also start with fresh object files.
+cc-fullversion-uncached := \
+ $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh -p $(CC))
+
+ifneq ($(cc-fullversion-uncached),$(cc-fullversion))
+ $(error Detected new CC version ($(cc-fullversion-uncached) vs $(cc-fullversion)). Please 'make clean')
+endif
+
# Read in config
-include include/config/auto.conf
Several people reported that the commit 3298b690b21c ("kbuild: Add a cache for generated variables") caused them problems when they updated gcc versions. Specifically the reports all looked something similar to this: > In file included from ./include/uapi/linux/uuid.h:21:0, > from ./include/linux/uuid.h:19, > from ./include/linux/mod_devicetable.h:12, > from scripts/mod/devicetable-offsets.c:2: > ./include/linux/string.h:8:20: fatal error: stdarg.h: No such file or > directory > #include <stdarg.h> Masahiro Yamada determined that the problem was with: NOSTDINC_FLAGS += -nostdinc -isystem $(call shell-cached,$(CC) -print-file-name=include) Specifically that the stale result of -print-file-name is stored in the cache file. It was determined that a "make clean" fixed the problems in all cases. In this particular case we could certainly try to clean just the cache when we detect a gcc update, but it seems like overall it's a bad idea to do an incremental build when gcc changes. We should warn the user and tell them that they need a 'make clean'. Fixes: 3298b690b21c ("kbuild: Add a cache for generated variables") Reported-by: Yang Shi <yang.s@alibaba-inc.com> Reported-by: Dave Hansen <dave.hansen@intel.com> Reported-by: Mathieu Malaterre <malat@debian.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> --- Changes in v3: - Fix as per Masahiro Yamada (move change to main Makefile) Changes in v2: - Don't error if MAKECMDGOALS is blank. Makefile | 9 +++++++++ 1 file changed, 9 insertions(+)