On Mon, Oct 2, 2023 at 3:20 PM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> -Wincompatible-function-pointer-types-strict aims to catch clang kernel
> Control Flow Integrity (kCFI) violations at build time (rather than run
> time) by validating function pointer assignments against the expected
> prototype, similar to the existing -Wincompatible-function-pointer-types
> that is considered a hard error in the kernel. The -strict variant
> requires the types to match exactly, as opposed to just matching in
> terms of ABI compatibility. This is primarily visible with int/unsigned
> int in lieu of enum types or vice versa.
>
> The tree is not completely clean, so this warning cannot currently be
> enabled unconditionally. However, there are only warnings in one
> subsystem ('drivers/counter'), so it is really close. In order to
> benefit from CI infrastructure that tests with W=1, enable this warning
> at that level, so that new instances have a chance of being caught and
> fixed during development.
>
> This should eventually be a hard error in a similar manner as
> Wincompatible-function-pointer-types but some subsystems test
> with W=1 + CONFIG_WERROR=n, so it would be rude to break their builds
> when they do not care about warnings outside of their subsystem.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Sounds like we're pretty close to just enabling this by default.
Getting it on in W=1 for a cycle will help prevent any backslide.
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> ---
> scripts/Makefile.extrawarn | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 2fe6f2828d37..9662f7fd6e39 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -108,6 +108,7 @@ KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow)
> KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation)
> KBUILD_CFLAGS += $(call cc-option, -Wstringop-overflow)
> KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
> +KBUILD_CFLAGS += $(call cc-option, -Wincompatible-function-pointer-types-strict)
>
> KBUILD_CPPFLAGS += -Wundef
> KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
>
> ---
> base-commit: ce9ecca0238b140b88f43859b211c9fdfd8e5b70
> change-id: 20231002-enable-wincompatible-function-pointer-types-strict-w-1-4a56b99b8c6f
>
> Best regards,
> --
> Nathan Chancellor <nathan@xxxxxxxxxx>
>
--
Thanks,
~Nick Desaulniers
