Re: [PATCH kbuild] kbuild: Allow to reduce the number of suffixes for clang thin-lto build

[Yonghong Song <yonghong.song@linux.dev>]

On 3/6/26 2:45 PM, Nathan Chancellor wrote:
> On Fri, Mar 06, 2026 at 02:12:44PM -0800, Yonghong Song wrote:
>> So you mean we do not need a new config. Should just check clang and
>> clang versionn like below?
>>
>> diff --git a/Makefile b/Makefile
>> index e944c6e71e81..9bd3990024c5 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -1034,6 +1034,11 @@ endif
>>   ifdef CONFIG_LTO_CLANG
>>   ifdef CONFIG_LTO_CLANG_THIN
>>   CC_FLAGS_LTO   := -flto=thin -fsplit-lto-unit
>> +ifdef CONFIG_CC_IS_CLANG
>> +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 230000; echo $$?),0)
> This is the same as
>
>    ifeq ($(call clang-min-version,230000),y)
>
> That being said, could we not just do a dynamic check so that it always
> works when these flags are supported?

Thanks for the suggestion! What you had below with 'call ld-option' is perfect
to satisfy this requirement: <= llvm22, two flags will be ignored, and
>= llvm23, two flags will be used.

v2: https://lore.kernel.org/linux-kbuild/20260307050250.3767489-1-yonghong.song@linux.dev/

>
>> +KBUILD_LDFLAGS += --lto-whole-program-visibility -mllvm -always-rename-promoted-locals=false
>    KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm -always-rename-promoted-locals=false)
>
>> +endif
>> +endif
>>   else
>>   CC_FLAGS_LTO   := -flto
>>   endif
>>
>> I think this should work. In rare case, renaming the function should
>> solve the problem.
> I agree with Josh that having this be the default behavior with the
> workarounds that we have available to us to avoid problems from it is
> worth it. Thanks for chasing this after the discussions at LPC.
>
> Cheers,
> Nathan