The use of an undefined macro in an #if directive is warned, but only in *.c files. No warning from other files such as *.S, *.lds.S. Since -Wundef is a preprocessor-related warning, it should be added to KBUILD_CPPFLAGS instead of KBUILD_CFLAGS. My previous attempt [1] uncovered several warnings, and could not finish fixing them all. This commit adds -Wundef to KBUILD_CPPFLAGS for W=1 builds in order to block new breakages. (The kbuild test robot tests with W=1) We can fix the warnings one by one. After we fix all of them, we can make this default in the top Makefile, and remove -Wundef from KBUILD_CFLAGS. [1]: https://lore.kernel.org/all/20221012180118.331005-2-masahiroy@xxxxxxxxxx/ Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> --- scripts/Makefile.extrawarn | 1 + 1 file changed, 1 insertion(+) diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 6bbba36c5969..40cd13eca82e 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -38,6 +38,7 @@ KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -Wno-type-limits KBUILD_CFLAGS += -Wno-shift-negative-value +KBUILD_CPPFLAGS += -Wundef KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 else -- 2.34.1
