Re: [PATCH v3 11/20] kbuild: avoid re-running compiler and linker probes

[Kees Cook <kees@kernel.org>]

On Thu, Sep 17, 2026 at 06:21:19PM -0700, Nathan Chancellor wrote:
> While we could certainly try to cook something like this up, we could
> also avoid the split across two files by just defining the flags in
> Kconfig directly and using them in the Makefile through their symbol,
> like we already do for -Wimplicit-fallthrough. For example, instead of
> 
>   config CC_HAS_STRICT_FLEX_ARRAYS
>       def_bool $(cc-option,-fstrict-flex-arrays=3)
> 
>   KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_STRICT_FLEX_ARRAYS),-fstrict-flex-arrays=3)
> 
> We would just do
> 
>   config CC_STRICT_FLEX_ARRAYS
>       string
>       default "-fstrict-flex-arrays=3" if $(cc-option,-fstrict-flex-arrays=3)
> 
>   KBUILD_CFLAGS += $(CONFIG_CC_STRICT_FLEX_ARRAYS)
> 
> While we still get the duplication (and we could look at getting rid of
> it with your cc-option-str idea or whatever), it is at least contained
> to the same location, so out of sync issues should be much rarer. I do
> diff Kconfigs so this might make certain issues with checks a little bit
> more obvious if something changes on the compiler side.

Yeah, and note that cc-option-bit already exists. It's just a weird name
is all and there isn't an ld-option-bit.

As for naming conventions, I think "CC_OPT_" would be a good prefix. And
this works today with no change:

config CC_OPT_STRICT_FLEX_ARRAYS
	string
	default "$(cc-option-bit,-fstrict-flex-arrays=3)"

(do we need "def_string" now?)

-- 
Kees Cook