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

[Alice Ryhl]

On Thu, Mar 19, 2026 at 12:47 PM Gary Guo <gary@xxxxxxxxxxx> wrote:
>
> 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.

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.

Alice