[PATCH 2/4] kbuild: Disable AutoFDO and Propeller flags for kernel modules

From: xur

Date: Fri Oct 10 2025 - 17:02:08 EST

From: Rong Xu <xur@xxxxxxxxxx>

AutoFDO and Propeller build currently does not support kernel modules,
but the corresponding build flags are still being set.

This change suppresses these build flags for modules. These flags can
be re-enabled once Propeller support for kernel modules is added.

Signed-off-by: Rong Xu <xur@xxxxxxxxxx>
---
Makefile | 9 +++++----
scripts/Makefile.autofdo | 9 ++++++---
scripts/Makefile.lib | 9 ++++++---
scripts/Makefile.propeller | 12 ++++++++----
scripts/Makefile.vmlinux_o | 2 +-
5 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/Makefile b/Makefile
index 6f88b1d3b40d9..f40bee23d5536 100644
--- a/Makefile
+++ b/Makefile
@@ -1230,14 +1230,15 @@ PHONY += vmlinux
# not for decompressors. LDFLAGS_vmlinux in arch/*/boot/compressed/Makefile is
# unrelated; the decompressors just happen to have the same base name,
# arch/*/boot/compressed/vmlinux.
-# Export LDFLAGS_vmlinux only to scripts/Makefile.vmlinux.
+# Export LDFLAGS_vmlinux only to scripts/Makefile.vmlinux, and
+# scripts/Makefile.vmlinux_o.
#
# _LDFLAGS_vmlinux is a workaround for the 'private export' bug:
# https://savannah.gnu.org/bugs/?61463
# For Make > 4.4, the following simple code will work:
-# vmlinux: private export LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
-vmlinux: private _LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
-vmlinux: export LDFLAGS_vmlinux = $(_LDFLAGS_vmlinux)
+# vmlinux vmlinux_o: private export LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
+vmlinux vmlinux_o: private _LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
+vmlinux vmlinux_o: export LDFLAGS_vmlinux = $(_LDFLAGS_vmlinux)
vmlinux: vmlinux.o $(KBUILD_LDS) modpost
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux

diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo
index 1caf2457e585c..5bcfcef273745 100644
--- a/scripts/Makefile.autofdo
+++ b/scripts/Makefile.autofdo
@@ -14,11 +14,14 @@ ifdef CLANG_AUTOFDO_PROFILE
endif

ifdef CONFIG_LTO_CLANG_THIN
+ _ldflags_autofdo := --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto
+ _ldflags_autofdo += -plugin-opt=-split-machine-functions
ifdef CLANG_AUTOFDO_PROFILE
- KBUILD_LDFLAGS += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE)
+ _ldflags_autofdo += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE)
endif
- KBUILD_LDFLAGS += --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto
- KBUILD_LDFLAGS += -plugin-opt=-split-machine-functions
+ # TODO: change LDFLAGS_vmlinux to KBUILD_LDFLAGS when kernel modules
+ # are supported.
+ LDFLAGS_vmlinux += $(_ldflags_autofdo)
endif

export CFLAGS_AUTOFDO_CLANG
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 53c02fc3b348a..0f6874e8d584d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -108,20 +108,23 @@ endif
#
# Enable AutoFDO build flags except some files or directories we don't want to
# enable (depends on variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE).
-#
+# TODO: change '$(part-of-builtin)' to '$(is-kernel-object)' when the AutoFDO
+# build supports modules.
ifeq ($(CONFIG_AUTOFDO_CLANG),y)
_c_flags += $(if $(patsubst n%,, \
- $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
+ $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(part-of-builtin)), \
$(CFLAGS_AUTOFDO_CLANG))
endif

#
# Enable Propeller build flags except some files or directories we don't want to
# enable (depends on variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE).
+# TODO: change '$(part-of-builtin)' to '$(is-kernel-object)' when the Propeller
+# build supports modules.
#
ifdef CONFIG_PROPELLER_CLANG
_c_flags += $(if $(patsubst n%,, \
- $(PROPELLER_PROFILE_$(target-stem).o)$(PROPELLER_PROFILE)$(is-kernel-object)), \
+ $(PROPELLER_PROFILE_$(target-stem).o)$(PROPELLER_PROFILE)$(part-of-builtin)), \
$(CFLAGS_PROPELLER_CLANG))
endif

diff --git a/scripts/Makefile.propeller b/scripts/Makefile.propeller
index 48a660128e256..fa018098506b8 100644
--- a/scripts/Makefile.propeller
+++ b/scripts/Makefile.propeller
@@ -3,7 +3,7 @@
# Enable available and selected Clang Propeller features.
ifdef CLANG_PROPELLER_PROFILE_PREFIX
CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=list=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt -ffunction-sections
- KBUILD_LDFLAGS += --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering
+ _ldflags_propeller := --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering
else
# Starting with Clang v20, the '-fbasic-block-sections=labels' option is
# deprecated. Use the recommended '-fbasic-block-address-map' option.
@@ -26,14 +26,18 @@ endif

ifdef CONFIG_LTO_CLANG_THIN
ifdef CLANG_PROPELLER_PROFILE_PREFIX
- KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
+ _ldflags_propeller += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
else
ifeq ($(call test-ge, $(CONFIG_LLD_VERSION), 200000),y)
- KBUILD_LDFLAGS += --lto-basic-block-address-map
+ _ldflags_propeller += --lto-basic-block-address-map
else
- KBUILD_LDFLAGS += --lto-basic-block-sections=labels
+ _ldflags_propeller += --lto-basic-block-sections=labels
endif
endif
endif

+# TODO: change LDFLAGS_vmlinux to KBUILD_LDFLAGS when kernel modules
+# are supported.
+LDFLAGS_vmlinux += $(_ldflags_propeller)
+
export CFLAGS_PROPELLER_CLANG
diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
index 23c8751285d79..9c4f0841e5c5d 100644
--- a/scripts/Makefile.vmlinux_o
+++ b/scripts/Makefile.vmlinux_o
@@ -56,7 +56,7 @@ vmlinux-o-ld-args-$(CONFIG_BUILTIN_MODULE_RANGES) += -Map=$@.map

quiet_cmd_ld_vmlinux.o = LD $@
cmd_ld_vmlinux.o = \
- $(LD) ${KBUILD_LDFLAGS} -r -o $@ \
+ $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_vmlinux) -r -o $@ \
$(vmlinux-o-ld-args-y) \
$(addprefix -T , $(initcalls-lds)) \
--whole-archive vmlinux.a --no-whole-archive \
--
2.51.0.740.g6adb054d12-goog