Re: [PATCH 4/4] scripts/Kconfig.toolchain: Document minimum supported versions for dynamic checks

[Julian Braha <julianbraha@gmail.com>]

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On 11/11/26 05:42, Nathan Chancellor wrote:
> To make it easier to clean up unnecessary dynamic checks when the
> minimum supported version of a toolchain component is updated, add
> comments documenting when features were first supported. Request that
> future additions document this as well.

Love, love, love this!

I tested the bounds and replicated nearly all of your results, but had a
few notes:

> 
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  scripts/Kconfig.toolchain | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/scripts/Kconfig.toolchain b/scripts/Kconfig.toolchain
> index 26a62b15e9ab..3a9eb8317d59 100644
> --- a/scripts/Kconfig.toolchain
> +++ b/scripts/Kconfig.toolchain
> @@ -1,4 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> +# When adding a new dynamic check (such as {cc,ld}-option{,-str} or testing a
> +# small program), please add a comment documenting the first version of the
> +# tool that supported the feature being tested. For cc-option{,-str}, note the
> +# "beware" comment below.
> +
>  config CC_VERSION_TEXT
>  	string
>  	default "$(CC_VERSION_TEXT)"
> @@ -118,6 +123,7 @@ config GCC_ASM_GOTO_OUTPUT_BROKEN
>  config CC_HAS_ASM_GOTO_OUTPUT
>  	def_bool y
>  	depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
> +	# supported since clang-10 and gcc-11

'asm goto' failed for me with clang 10. Seems it was added with
clang 11 [1]

>  	depends on $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
>  
>  config CC_HAS_ASM_GOTO_TIED_OUTPUT
> @@ -129,6 +135,7 @@ config TOOLS_SUPPORT_RELR
>  	def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
>  
>  config CC_HAS_ASM_INLINE
> +	# supported since clang-11 and gcc-9
>  	def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
>  
>  config CC_HAS_ASSUME
> @@ -161,6 +168,8 @@ config CC_HAS_ASSUME
>  #    pitfall.
>  
>  config CC_OPT_ZERO_INIT_PADDING_BITS
> +	# supported since gcc-15. not needed for clang, as it does this by default since clang-20
> +	# https://github.com/llvm/llvm-project/
> commit/7a086e1b2dc05f54afae3591614feede727601fa
>  	def_string "$(cc-option-str,-fzero-init-padding-bits=all)"
>  
>  config CC_OPT_NO_ADDRSIG
> @@ -168,12 +177,15 @@ config CC_OPT_NO_ADDRSIG
>  	def_string "-fno-addrsig" if CC_IS_CLANG
>  
>  config CC_OPT_DIAGNOSTICS_SHOW_CONTEXT
> +	# supported since gcc-16, not supported by clang
>  	def_string "$(cc-option-str,-fdiagnostics-show-context=2)"
>  
>  config CC_OPT_DIAGNOSTICS_SHOW_INLINING_CHAIN
> +	# supported since clang-23. not needed for gcc, as it does this by default
>  	def_string "$(cc-option-str,-fdiagnostics-show-inlining-chain)"
>  
>  config CC_OPT_STRICT_FLEX_ARRAYS
> +	# supported since clang-16 and gcc-13
>  	def_string "$(cc-option-str,-fstrict-flex-arrays=3)"

Clang 15 supports '-fstrict-flex-arrays' [1] so the check seemingly
passed, but support for level 3 wasn't actually added until clang 16.

I think this needs a:
    'depends on !CC_IS_CLANG || CLANG_VERSION >= 160000'
so the option evaluates as empty string when these deps are unmet.

>  
>  config CC_OPT_NO_ALLOW_STORE_DATA_RACES
> @@ -181,51 +193,67 @@ config CC_OPT_NO_ALLOW_STORE_DATA_RACES
>  	def_string "$(cc-option-str,-fno-allow-store-data-races,--param=allow-store-data-races=0)" if CC_IS_GCC
>  
>  config CC_HAS_MNOP_MCOUNT
> +	# supported since clang-10 and gcc-9 but option is architecture specific
>  	def_bool $(cc-option,-mnop-mcount)

'-mnop-mcount' worked for me on x86 with gcc 5 [3], but it seems s390
support came later in v9 [4]

>  
>  config LD_OPT_FORCE_GROUP_ALLOCATION
> +	# supported since ld.lld 19 and GNU ld 2.29
>  	def_string "$(ld-option-str,--force-group-allocation)"
>  
>  config LD_OPT_NO_WARN_RWX_SEGMENTS
> +	# supported since GNU ld 2.39, not supported by ld.lld
>  	def_string "$(ld-option-str,--no-warn-rwx-segments)"
>  
>  config CC_OPT_WNO_ADDRESS_OF_PACKED_MEMBER
> +	# supported since clang-4 and gcc-9
>  	def_string "$(cc-option-str,-Wno-address-of-packed-member)"
>  
>  config CC_OPT_WNO_FORMAT_OVERFLOW_NON_KPRINTF
> +	# supported since clang-18, not needed for gcc
>  	def_string "$(cc-option-str,-Wno-format-overflow-non-kprintf)"
>  
>  config CC_OPT_WNO_FORMAT_TRUNCATION_NON_KPRINTF
> +	# supported since clang-18, not needed for gcc
>  	def_string "$(cc-option-str,-Wno-format-truncation-non-kprintf)"
>  
>  config CC_OPT_WNO_DEFAULT_CONST_INIT_UNSAFE
> +	# supported since clang-21, not needed for gcc
>  	def_string "$(cc-option-str,-Wno-default-const-init-unsafe)"
>  
>  config CC_OPT_WNO_DANGLING_POINTER
> +	# supported since gcc-12, not needed for clang
>  	def_string "$(cc-option-str,-Wno-dangling-pointer)"
>  
>  config CC_OPT_WVLA_LARGER_THAN
> +	# supported since gcc-7, not supported by clang
>  	def_string "$(cc-option-str,-Wvla-larger-than=1)"
>  
>  config CC_HAS_WSTRINGOP_OVERFLOW
> +	# supported since gcc-7, not supported by clang
>  	def_bool $(cc-option,-Wstringop-overflow)
>  
>  config CC_OPT_WNO_UNTERMINATED_STRING_INITIALIZATION
> +	# supported since gcc-15 and clang-21
>  	def_string "$(cc-option-str,-Wno-unterminated-string-initialization)"
>  
>  config CC_OPT_WERROR_DESIGNATED_INIT
> +	# supported since gcc-5, not supported by clang
>  	def_string "$(cc-option-str,-Werror=designated-init)"
>  
>  config CC_OPT_WENUM_CONVERSION
> +	# supported since clang-3.2 and gcc-10
>  	def_string "$(cc-option-str,-Wenum-conversion)"
>  
>  config CC_OPT_WNO_PACKED_NOT_ALIGNED
> +	# supported since gcc-8, not supported by clang
>  	def_string "$(cc-option-str,-Wno-packed-not-aligned)"
>  
>  config CC_OPT_WNO_FORMAT_OVERFLOW
> +	# supported since gcc-7 and clang-18
>  	def_string "$(cc-option-str,-Wno-format-overflow)"
>  
>  config CC_OPT_WNO_STRINGOP_TRUNCATION
> +	# supported since gcc-8, not supported by clang
>  	def_string "$(cc-option-str,-Wno-stringop-truncation)"
>  
>  config CC_HAS_COUNTED_BY
> @@ -252,14 +280,18 @@ config CC_HAS_BROKEN_COUNTED_BY_REF
>  	default y if CC_IS_CLANG && CLANG_VERSION < 220100
>  
>  config CC_HAS_ALLOC_TOKEN
> +	# supported since clang-22, not supported by gcc
>  	def_bool $(cc-option,-falloc-token-max=123)
>  
>  config CC_HAS_MULTIDIMENSIONAL_NONSTRING
> +	# supported since gcc-15 and clang-21
>  	def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
>  
>  config CC_OPT_INLINE_MEMSET
>  	string
> +	# supported since gcc-14
>  	default "-finline-stringops=memset" if $(cc-option,-finline-stringops=memset)
> +	# supported since clang-22
>  	default "-mllvm -max-store-memset=4294967294" if $(cc-option,-mllvm -max-store-memset=4294967294)
>  
>  config LD_CAN_USE_KEEP_IN_OVERLAY
> 
> -- 2.56.0
> 

[1]
https://releases.llvm.org/11.0.0/tools/clang/docs/LanguageExtensions.html
[2]
https://releases.llvm.org/15.0.0/tools/clang/docs/ReleaseNotes.html#major-new-features
[3] https://gcc.gnu.org/gcc-5/changes.html#x86
[4] https://gcc.gnu.org/gcc-9/changes.html#s390

- Julian Braha




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