From 9f2aee8f7d1842be08da860e45265d30dba0d1f7 Mon Sep 17 00:00:00 2001 From: Rong Xu Date: Fri, 29 May 2026 11:53:46 -0700 Subject: kbuild: distributed build support for Clang ThinLTO 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 Co-developed-by: Masahiro Yamada Signed-off-by: Masahiro Yamada Tested-by: Piotr Gorski Tested-by: Nathan Chancellor Link: https://patch.msgid.link/20260529185347.2418373-4-xur@google.com Signed-off-by: Nathan Chancellor --- scripts/Makefile.vmlinux_a | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'scripts/Makefile.vmlinux_a') diff --git a/scripts/Makefile.vmlinux_a b/scripts/Makefile.vmlinux_a index 650d44330d1f..bd141b893748 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 -Fqx $${obj} $(word 2, $^); then \ + echo $${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. # --------------------------------------------------------------------------- -- cgit