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

[Gary Guo]

On Thu Mar 19, 2026 at 11:44 AM GMT, Alice Ryhl wrote:
> On Thu, Mar 19, 2026 at 12:31 PM Gary Guo <gary@xxxxxxxxxxx> wrote:
>>
>> On Thu Mar 19, 2026 at 11:22 AM GMT, Alice Ryhl wrote:
>> > This patch enables AutoFDO build support for Rust code within the Linux
>> > kernel. This allows Rust code to be profiled and optimized based on the
>> > profile.
>> >
>> > This was verified by inspecting the object files and confirming that
>> > they look correct. It was also verified in conjuction with my helpers
>> > inlining series, and it also appears to have worked correctly when
>> > combined with that series once one missing thing [1] was fixed in the
>> > helpers inlining series.
>> >
>> > Link: https://lore.kernel.org/all/aasPsbMEsX6iGUl8@xxxxxxxxxx/ [1]
>> > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>> > ---
>> >  scripts/Makefile.autofdo | 6 +++++-
>> >  scripts/Makefile.lib     | 3 +++
>> >  2 files changed, 8 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo
>> > index 1caf2457e585..3f08acab4549 100644
>> > --- a/scripts/Makefile.autofdo
>> > +++ b/scripts/Makefile.autofdo
>> > @@ -3,14 +3,18 @@
>> >  # Enable available and selected Clang AutoFDO features.
>> >
>> >  CFLAGS_AUTOFDO_CLANG := -fdebug-info-for-profiling -mllvm -enable-fs-discriminator=true -mllvm -improved-fs-discriminator=true
>> > +RUSTFLAGS_AUTOFDO_CLANG := -Zdebug-info-for-profiling -Cllvm-args=-enable-fs-discriminator=true -Cllvm-args=-improved-fs-discriminator=true
>>
>> I get that it's currently named as AUTOFDO_CLANG, but this really ought to be
>> AUTOFDO_LLVM...
>>
>> The flag translations look correct to me.
>
> 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.

Best,
Gary