[PATCH] kbuild: rust: add AutoFDO support

[Alice Ryhl]

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
 
 ifndef CONFIG_DEBUG_INFO
   CFLAGS_AUTOFDO_CLANG += -gmlt
+  RUSTFLAGS_AUTOFDO_CLANG += -Cdebuginfo=line-tables-only
 endif
 
 ifdef CLANG_AUTOFDO_PROFILE
   CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections
   CFLAGS_AUTOFDO_CLANG += -fsplit-machine-functions
+  RUSTFLAGS_AUTOFDO_CLANG += -Zprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -Zfunction-sections=y
+  RUSTFLAGS_AUTOFDO_CLANG += -Cllvm-args=-split-machine-functions
 endif
 
 ifdef CONFIG_LTO_CLANG_THIN
@@ -21,4 +25,4 @@ ifdef CONFIG_LTO_CLANG_THIN
   KBUILD_LDFLAGS += -plugin-opt=-split-machine-functions
 endif
 
-export CFLAGS_AUTOFDO_CLANG
+export CFLAGS_AUTOFDO_CLANG RUSTFLAGS_AUTOFDO_CLANG
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0718e39cedda..eaddf6637669 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -123,6 +123,9 @@ ifeq ($(CONFIG_AUTOFDO_CLANG),y)
 _c_flags += $(if $(patsubst n%,, \
 	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
 	$(CFLAGS_AUTOFDO_CLANG))
+_rust_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
+	$(RUSTFLAGS_AUTOFDO_CLANG))
 endif
 
 #

---
base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
change-id: 20260309-autofdo-8d01e7977fed

Best regards,
-- 
Alice Ryhl <aliceryhl@xxxxxxxxxx>