[PATCH v6 0/2] kbuild: distributed build support for Clang ThinLTO

[PATCH v6 0/2] kbuild: distributed build support for Clang ThinLTO

[xur]

From: Rong Xu <xur@google.com>

ChangeLog:

V6: Change '--thin' back to 'T' in Makefile.vmlinux_a to fix
    reported the build error from old ar.
V5: Handle single quote escaping in echo _c_flags to fix
    Piotr Gorski's reported error.

V4: This is based on the reimplementation provided by Masahiro Yamada
on May 26. The difference is that this version now saves the compiler
flags (_c_flags) from the Front-End (FE) compilation and re-uses them
for the subsequent Back-End (BE) compilation.

Rong Xu (2):
  kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a
  kbuild: distributed build support for Clang ThinLTO

 .gitignore                 |  2 +
 Makefile                   | 25 +++++-------
 arch/Kconfig               | 19 +++++++++
 scripts/Makefile.lib       |  7 ++++
 scripts/Makefile.thinlto   | 40 ++++++++++++++++++
 scripts/Makefile.vmlinux_a | 83 ++++++++++++++++++++++++++++++++++++++
 scripts/mod/modpost.c      | 15 +++++--
 7 files changed, 174 insertions(+), 17 deletions(-)
 create mode 100644 scripts/Makefile.thinlto
 create mode 100644 scripts/Makefile.vmlinux_a


base-commit: 2d1373e4246da3b58e1df058374ed6b101804e07
-- 
2.53.0.851.ga537e3e6e9-goog

[PATCH v6 1/2] kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a

[xur]

From: Rong Xu <xur@google.com>

From: Masahiro Yamada <masahiroy@kernel.org>

Move the build rule for vmlinux.a to a separate file in preparation
for supporting distributed builds with Clang ThinLTO.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Rong Xu <xur@google.com>
Signed-off-by: Rong Xu <xur@google.com>
Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
---
 Makefile                   | 16 +++++--------
 scripts/Makefile.vmlinux_a | 46 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 10 deletions(-)
 create mode 100644 scripts/Makefile.vmlinux_a

diff --git a/Makefile b/Makefile
index c9b7bee102e8..ba5eee68d5d2 100644
--- a/Makefile
+++ b/Makefile
@@ -1255,7 +1255,7 @@ export ARCH_DRIVERS	:= $(drivers-y) $(drivers-m)
 KBUILD_VMLINUX_OBJS := built-in.a $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
 KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
 
-export KBUILD_VMLINUX_LIBS
+export KBUILD_VMLINUX_OBJS KBUILD_VMLINUX_LIBS
 export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
 
 ifdef CONFIG_TRIM_UNUSED_KSYMS
@@ -1264,16 +1264,12 @@ ifdef CONFIG_TRIM_UNUSED_KSYMS
 KBUILD_MODULES := y
 endif
 
-# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
-quiet_cmd_ar_vmlinux.a = AR      $@
-      cmd_ar_vmlinux.a = \
-	rm -f $@; \
-	$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
-	$(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
+PHONY += vmlinux_a
+vmlinux_a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_a
 
-targets += vmlinux.a
-vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
-	$(call if_changed,ar_vmlinux.a)
+vmlinux.a: vmlinux_a
+	@:
 
 PHONY += vmlinux_o
 vmlinux_o: vmlinux.a $(KBUILD_VMLINUX_LIBS)
diff --git a/scripts/Makefile.vmlinux_a b/scripts/Makefile.vmlinux_a
new file mode 100644
index 000000000000..650d44330d1f
--- /dev/null
+++ b/scripts/Makefile.vmlinux_a
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+PHONY := __default
+__default: vmlinux.a
+
+include include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+include $(srctree)/scripts/Makefile.lib
+
+# Link of built-in-fixup.a
+# ---------------------------------------------------------------------------
+
+# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
+quiet_cmd_ar_builtin_fixup = AR      $@
+      cmd_ar_builtin_fixup = \
+	rm -f $@; \
+	$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
+	$(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
+
+targets += built-in-fixup.a
+built-in-fixup.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
+	$(call if_changed,ar_builtin_fixup)
+
+# vmlinux.a
+# ---------------------------------------------------------------------------
+
+targets += vmlinux.a
+vmlinux.a: built-in-fixup.a FORCE
+	$(call if_changed,copy)
+
+# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
+# ---------------------------------------------------------------------------
+
+PHONY += FORCE
+FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building above, using $(if_changed{,_dep}). As an
+# optimization, we don't need to read them if the target does not
+# exist, we will rebuild anyway in that case.
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)
-- 
2.53.0.851.ga537e3e6e9-goog

[PATCH v6 2/2] kbuild: distributed build support for Clang ThinLTO

[xur]

From: Rong Xu <xur@google.com>

Add distributed ThinLTO build support for the Linux kernel.
This new mode offers several advantages: (1) Increased
flexibility in handling user-specified build options.
(2) Improved user-friendliness for developers. (3) Greater
convenience for integrating with objtool and livepatch.

Note that "distributed" in this context refers to a term
that differentiates in-process ThinLTO builds by invoking
backend compilation through the linker, not necessarily
building in distributed environments.

Distributed ThinLTO is enabled via the
`CONFIG_LTO_CLANG_THIN_DIST` Kconfig option. For example:
 > make LLVM=1 defconfig
 > scripts/config -e LTO_CLANG_THIN_DIST
 > make LLVM=1 oldconfig
 > make LLVM=1 vmlinux -j <..>

The build flow proceeds in four stages:
  1. Perform FE compilation, mirroring the in-process ThinLTO mode.
  2. Thin-link the generated IR files and object files.
  3. Find all IR files and perform BE compilation, using the flags
    stored in the .*.o.cmd files.
  4. Link the BE results to generate the final vmlinux.o.

NOTE: This patch currently implements the build for the main kernel
image (vmlinux) only. Kernel module support is planned for a
subsequent patch.

Tested on the following arch: x86, arm64, loongarch, and
riscv.

The earlier implementation details can be found here:
https://discourse.llvm.org/t/rfc-distributed-thinlto-build-for-kernel/85934

Signed-off-by: Rong Xu <xur@google.com>
Co-developed-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
---
 .gitignore                 |  2 ++
 Makefile                   |  9 +++++----
 arch/Kconfig               | 19 ++++++++++++++++++
 scripts/Makefile.lib       |  7 +++++++
 scripts/Makefile.thinlto   | 40 ++++++++++++++++++++++++++++++++++++++
 scripts/Makefile.vmlinux_a | 37 +++++++++++++++++++++++++++++++++++
 scripts/mod/modpost.c      | 15 +++++++++++---
 7 files changed, 122 insertions(+), 7 deletions(-)
 create mode 100644 scripts/Makefile.thinlto

diff --git a/.gitignore b/.gitignore
index 3a7241c941f5..c12bdf5a97f9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,6 +56,7 @@
 *.zst
 Module.symvers
 dtbs-list
+builtin.order
 modules.order
 
 #
@@ -67,6 +68,7 @@ modules.order
 /vmlinux.32
 /vmlinux.map
 /vmlinux.symvers
+/vmlinux.thinlto-index
 /vmlinux.unstripped
 /vmlinux-gdb.py
 /vmlinuz
diff --git a/Makefile b/Makefile
index ba5eee68d5d2..4a399b7f3b48 100644
--- a/Makefile
+++ b/Makefile
@@ -1033,10 +1033,10 @@ export CC_FLAGS_SCS
 endif
 
 ifdef CONFIG_LTO_CLANG
-ifdef CONFIG_LTO_CLANG_THIN
-CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
-else
+ifdef CONFIG_LTO_CLANG_FULL
 CC_FLAGS_LTO	:= -flto
+else
+CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
 endif
 CC_FLAGS_LTO	+= -fvisibility=hidden
 
@@ -1648,6 +1648,7 @@ endif # CONFIG_MODULES
 CLEAN_FILES += vmlinux.symvers modules-only.symvers \
 	       modules.builtin modules.builtin.modinfo modules.nsdeps \
 	       modules.builtin.ranges vmlinux.o.map vmlinux.unstripped \
+	       vmlinux.thinlto-index builtin.order \
 	       compile_commands.json rust/test \
 	       rust-project.json .vmlinux.objs .vmlinux.export.c \
                .builtin-dtbs-list .builtin-dtb.S
@@ -2109,7 +2110,7 @@ clean: $(clean-dirs)
 	$(call cmd,rmfiles)
 	@find . $(RCS_FIND_IGNORE) \
 		\( -name '*.[aios]' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
-		-o -name '*.ko.*' \
+		-o -name '*.ko.*' -o -name '*.o.thinlto.bc' \
 		-o -name '*.dtb' -o -name '*.dtbo' \
 		-o -name '*.dtb.S' -o -name '*.dtbo.S' \
 		-o -name '*.dt.yaml' -o -name 'dtbs-list' \
diff --git a/arch/Kconfig b/arch/Kconfig
index 102ddbd4298e..340550e44c50 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -861,6 +861,25 @@ config LTO_CLANG_THIN
 	    https://clang.llvm.org/docs/ThinLTO.html
 
 	  If unsure, say Y.
+
+config LTO_CLANG_THIN_DIST
+	bool "Clang ThinLTO in distributed mode (EXPERIMENTAL)"
+	depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
+	select LTO_CLANG
+	help
+	  This option enables Clang's ThinLTO in distributed build mode.
+	  In this mode, the linker performs the thin-link, generating
+	  ThinLTO index files. Subsequently, the build system explicitly
+	  invokes ThinLTO backend compilation using these index files
+	  and pre-linked IR objects. The resulting native object files
+	  are with the .thinlto-native.o suffix.
+
+	  This build mode offers improved visibility into the ThinLTO
+	  process through explicit subcommand exposure. It also makes
+	  final native object files directly available, benefiting
+	  tools like objtool and kpatch. Additionally, it provides
+	  crucial granular control over back-end options, enabling
+	  module-specific compiler options, and simplifies debugging.
 endchoice
 
 config ARCH_SUPPORTS_AUTOFDO_CLANG
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0718e39cedda..b36c7c6817bd 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -249,6 +249,12 @@ ifdef CONFIG_LTO_CLANG
 cmd_ld_single = $(if $(objtool-enabled)$(is-single-obj-m), ; $(LD) $(ld_flags) -r -o $(tmp-target) $@; mv $(tmp-target) $@)
 endif
 
+ifdef CONFIG_LTO_CLANG_THIN_DIST
+# Save the _c_flags, sliently.
+quiet_cmd_save_c_flags =
+      cmd_save_c_flags = printf '\n%s\n' 'saved_c_flags_$@ := $(call escsq,$(_c_flags))' >> $(dot-target).cmd
+endif
+
 quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
       cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $< \
 		$(cmd_ld_single) \
@@ -256,6 +262,7 @@ quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
 
 define rule_cc_o_c
 	$(call cmd_and_fixdep,cc_o_c)
+	$(call cmd,save_c_flags)
 	$(call cmd,checksrc)
 	$(call cmd,checkdoc)
 	$(call cmd,gen_objtooldep)
diff --git a/scripts/Makefile.thinlto b/scripts/Makefile.thinlto
new file mode 100644
index 000000000000..03349ac69de5
--- /dev/null
+++ b/scripts/Makefile.thinlto
@@ -0,0 +1,40 @@
+PHONY := __default
+__default:
+
+include include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+include $(srctree)/scripts/Makefile.lib
+
+native-objs := $(patsubst %.o,%.thinlto-native.o,$(call read-file, vmlinux.thinlto-index))
+
+__default: $(native-objs)
+
+# Generate .thinlto-native.o (obj) from .o (bitcode) and .thinlto.bc (summary) files
+# ---------------------------------------------------------------------------
+quiet_cmd_cc_o_bc = CC $(quiet_modtag)  $@
+      be_flags = $(shell sed -n '/saved_c_flags_/s/.*:= //p' \
+		 $(dir $(<)).$(notdir $(<)).cmd)
+      cmd_cc_o_bc = \
+      $(CC) $(be_flags) -x ir -fno-lto -Wno-unused-command-line-argument \
+      -fthinlto-index=$(word 2, $^) -c -o $@ $<
+
+targets += $(native-objs)
+$(native-objs): %.thinlto-native.o: %.o %.o.thinlto.bc   FORCE
+	$(call if_changed,cc_o_bc)
+
+# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
+# ---------------------------------------------------------------------------
+
+PHONY += FORCE
+FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building above, using $(if_changed{,_dep}). As an
+# optimization, we don't need to read them if the target does not
+# exist, we will rebuild anyway in that case.
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)
diff --git a/scripts/Makefile.vmlinux_a b/scripts/Makefile.vmlinux_a
index 650d44330d1f..15d92ee82dee 100644
--- a/scripts/Makefile.vmlinux_a
+++ b/scripts/Makefile.vmlinux_a
@@ -21,6 +21,41 @@ targets += built-in-fixup.a
 built-in-fixup.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
 	$(call if_changed,ar_builtin_fixup)
 
+ifdef CONFIG_LTO_CLANG_THIN_DIST
+
+quiet_cmd_builtin.order = GEN     $@
+      cmd_builtin.order = $(AR) t $< > $@
+
+targets += builtin.order
+builtin.order: built-in-fixup.a FORCE
+	$(call if_changed,builtin.order)
+
+quiet_cmd_ld_thinlto_index = LD      $@
+      cmd_ld_thinlto_index = \
+	$(LD) $(KBUILD_LDFLAGS) -r --thinlto-index-only=$@ @$<
+
+targets += vmlinux.thinlto-index
+vmlinux.thinlto-index: builtin.order FORCE
+	$(call if_changed,ld_thinlto_index)
+
+quiet_cmd_ar_vmlinux.a = GEN     $@
+      cmd_ar_vmlinux.a =					\
+	rm -f $@;						\
+	while read -r obj; do					\
+		if grep -q $${obj} $(word 2, $^); then		\
+			echo $${obj%.o}.thinlto-native.o;	\
+		else						\
+			echo $${obj};				\
+		fi;						\
+	done < $< | xargs $(AR) cDPrS --thin $@
+
+targets += vmlinux.a
+vmlinux.a: builtin.order vmlinux.thinlto-index FORCE
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.thinlto
+	$(call if_changed,ar_vmlinux.a)
+
+else
+
 # vmlinux.a
 # ---------------------------------------------------------------------------
 
@@ -28,6 +63,8 @@ targets += vmlinux.a
 vmlinux.a: built-in-fixup.a FORCE
 	$(call if_changed,copy)
 
+endif
+
 # Add FORCE to the prerequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
 
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 0c25b5ad497b..b3c3cf42c9eb 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1482,13 +1482,22 @@ static void extract_crcs_for_object(const char *object, struct module *mod)
 	char cmd_file[PATH_MAX];
 	char *buf, *p;
 	const char *base;
-	int dirlen, ret;
+	int dirlen, baselen_without_suffix, ret;
 
 	base = get_basename(object);
 	dirlen = base - object;
 
-	ret = snprintf(cmd_file, sizeof(cmd_file), "%.*s.%s.cmd",
-		       dirlen, object, base);
+	baselen_without_suffix = strlen(object) - dirlen - strlen(".o");
+
+	/*
+	 * When CONFIG_LTO_CLANG_THIN_DIST=y, the ELF is *.thinlto-native.o
+	 * but the symbol CRCs are recorded in *.o.cmd file.
+	 */
+	if (strends(object, ".thinlto-native.o"))
+		baselen_without_suffix -= strlen(".thinlto-native");
+
+	ret = snprintf(cmd_file, sizeof(cmd_file), "%.*s.%.*s.o.cmd",
+		       dirlen, object, baselen_without_suffix, base);
 	if (ret >= sizeof(cmd_file)) {
 		error("%s: too long path was truncated\n", cmd_file);
 		return;
-- 
2.53.0.851.ga537e3e6e9-goog

Re: [PATCH v6 1/2] kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a

[Nicolas Schier]

On Mon, 16 Mar 2026 21:29:29 +0000, xur@google.com <xur@google.com> wrote:

Hi Rong,

> Move the build rule for vmlinux.a to a separate file in preparation
> for supporting distributed builds with Clang ThinLTO.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Tested-by: Rong Xu <xur@google.com>

As Masahiro's original patch is now being modified: I'd like to add
something like

[rong xu: change '--thin' back to 'T' in Makefile.vmlinux_a]

here before your 'Signed-off-by'.  Are you ok with that?

Kind regards,
Nicolas

-- 
Nicolas

Re: [PATCH v6 1/2] kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a

[Rong Xu]

Sounds good to me.

Could you also include a note stating that the '-T' flag is no longer
problematic since the minimum requirement for LLVM has been updated to
version 15? As of LLVM 14 and onward, the '-T' flag functions
identically to the '--thin' flag.

Thanks a lot for the help!

-Rong


On Wed, Mar 25, 2026 at 12:22 PM Nicolas Schier <nsc@kernel.org> wrote:
>
> On Mon, 16 Mar 2026 21:29:29 +0000, xur@google.com <xur@google.com> wrote:
>
> Hi Rong,
>
> > Move the build rule for vmlinux.a to a separate file in preparation
> > for supporting distributed builds with Clang ThinLTO.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > Tested-by: Rong Xu <xur@google.com>
>
> As Masahiro's original patch is now being modified: I'd like to add
> something like
>
> [rong xu: change '--thin' back to 'T' in Makefile.vmlinux_a]
>
> here before your 'Signed-off-by'.  Are you ok with that?
>
> Kind regards,
> Nicolas
>
> --
> Nicolas
>

Re: [PATCH v6 2/2] kbuild: distributed build support for Clang ThinLTO

[Nicolas Schier]

On Mon, Mar 16, 2026 at 09:29:30PM +0000, xur@google.com wrote:
> From: Rong Xu <xur@google.com>
> 
> Add distributed ThinLTO build support for the Linux kernel.
> This new mode offers several advantages: (1) Increased
> flexibility in handling user-specified build options.
> (2) Improved user-friendliness for developers. (3) Greater
> convenience for integrating with objtool and livepatch.
> 
> Note that "distributed" in this context refers to a term
> that differentiates in-process ThinLTO builds by invoking
> backend compilation through the linker, not necessarily
> building in distributed environments.
> 
> Distributed ThinLTO is enabled via the
> `CONFIG_LTO_CLANG_THIN_DIST` Kconfig option. For example:
>  > make LLVM=1 defconfig
>  > scripts/config -e LTO_CLANG_THIN_DIST
>  > make LLVM=1 oldconfig
>  > make LLVM=1 vmlinux -j <..>
> 
> The build flow proceeds in four stages:
>   1. Perform FE compilation, mirroring the in-process ThinLTO mode.
>   2. Thin-link the generated IR files and object files.
>   3. Find all IR files and perform BE compilation, using the flags
>     stored in the .*.o.cmd files.
>   4. Link the BE results to generate the final vmlinux.o.
> 
> NOTE: This patch currently implements the build for the main kernel
> image (vmlinux) only. Kernel module support is planned for a
> subsequent patch.
> 
> Tested on the following arch: x86, arm64, loongarch, and
> riscv.
> 
> The earlier implementation details can be found here:
> https://discourse.llvm.org/t/rfc-distributed-thinlto-build-for-kernel/85934
> 
> Signed-off-by: Rong Xu <xur@google.com>
> Co-developed-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  .gitignore                 |  2 ++
>  Makefile                   |  9 +++++----
>  arch/Kconfig               | 19 ++++++++++++++++++
>  scripts/Makefile.lib       |  7 +++++++
>  scripts/Makefile.thinlto   | 40 ++++++++++++++++++++++++++++++++++++++
>  scripts/Makefile.vmlinux_a | 37 +++++++++++++++++++++++++++++++++++
>  scripts/mod/modpost.c      | 15 +++++++++++---
>  7 files changed, 122 insertions(+), 7 deletions(-)
>  create mode 100644 scripts/Makefile.thinlto
> 
> diff --git a/.gitignore b/.gitignore
> index 3a7241c941f5..c12bdf5a97f9 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -56,6 +56,7 @@
>  *.zst
>  Module.symvers
>  dtbs-list
> +builtin.order
>  modules.order
>  
>  #
> @@ -67,6 +68,7 @@ modules.order
>  /vmlinux.32
>  /vmlinux.map
>  /vmlinux.symvers
> +/vmlinux.thinlto-index
>  /vmlinux.unstripped
>  /vmlinux-gdb.py
>  /vmlinuz
> diff --git a/Makefile b/Makefile
> index ba5eee68d5d2..4a399b7f3b48 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1033,10 +1033,10 @@ export CC_FLAGS_SCS
>  endif
>  
>  ifdef CONFIG_LTO_CLANG
> -ifdef CONFIG_LTO_CLANG_THIN
> -CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
> -else
> +ifdef CONFIG_LTO_CLANG_FULL
>  CC_FLAGS_LTO	:= -flto
> +else
> +CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
>  endif
>  CC_FLAGS_LTO	+= -fvisibility=hidden
>  

This hunk does not apply on kbuild-next-unstable [1] (a possible
conflict resolution: [2]).  Can you please rebase the patch set on
kbuild-next-unstable as Nathan suggested [3] ?

Thanks and kind regards
Nicolas

[1]: https://git.kernel.org/kbuild/l/kbuild-next-unstable
[2]: https://git.kernel.org/nsc/kbuild/c/505471374cfb107
[3]: https://lore.kernel.org/linux-kbuild/20260316204311.GA1329928@ax162/