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/mod/modpost.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) (limited to 'scripts/mod') diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 0d2f1f09019b..da0f4bc75509 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -1487,13 +1487,22 @@ 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; -- cgit v1.2.3