Re: [PATCH] kbuild: rust: add AutoFDO support

["Gary Guo" <gary@garyguo.net>]

On Thu Mar 19, 2026 at 11:54 PM GMT, Nathan Chancellor wrote:
> On Thu, Mar 19, 2026 at 07:09:22PM +0000, Gary Guo wrote:
>> On Thu Mar 19, 2026 at 4:33 PM GMT, Alice Ryhl wrote:
>> > On Thu, Mar 19, 2026 at 12:47 PM Gary Guo <gary@garyguo.net> wrote:
>> >> On Thu Mar 19, 2026 at 11:44 AM GMT, Alice Ryhl wrote:
>> >> > Do you think it's worth having Rust not match the CFLAGS here?
>> >> >
>> >>
>> >> I think the C flags should probably be renamed AUTOFDO_LLVM too. After call, all
>> >> the perf tools involved here are called llvm-foobar as well.
>> >
>> > But isn't it just called this because the config option is
>> > CONFIG_AUTOFDO_CLANG? So it's the CFLAGS or RUSTFLAGS related to that
>> > particular config option. It may make sense to rename
>> > CONFIG_AUTOFDO_CLANG to CONFIG_AUTOFDO, but that's out-of-scope for
>> > this change, in my opinion.
>> 
>> I get that it's an existing config name, but previously it is a correct
>> description, while after this change it is no longer accurate.
>> 
>> I don't know if there's an established practice on renaming CONFIG options when
>> this sort thing happens though. Perhaps one way is to have add
>> CONFIG_AUTOFDO_CLANG that selects CONFIG_AUTOFDO.
>
> As Miguel mentioned, there is the transitional keyword for Kconfig to
> handle renames now but I would really like there to be a compelling
> reason for the rename other than LLVM is a little more accurate than
> CLANG. The kernel has never really done a great job of referring to
> Clang when it means the C compiler vs. the whole LLVM toolchain (like
> LTO_CLANG and all its derivatives should be LTO_LLVM since it requires
> ld.lld, llvm-nm, and llvm-ar in addition to clang). Additionally, aside
> from the configuration, there is the user facing Make variable
> CLANG_AUTOFDO_PROFILE that would presumably need to be changed for
> consistency.

If you think the config name should be kept as CONFIG_AUTOFDO_CLANG, then I
think there is no real benefit in changing the variable name.

Reviewed-by: Gary Guo <gary@garyguo.net>

Best,
Gary