From a00cdb54dec79d56b3423a02a8fcea3dcba66af0 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Wed, 8 Apr 2020 10:36:23 +0900 Subject: [PATCH] BACKPORT: kbuild: support LLVM=1 to switch the default tools to Clang/LLVM commit a0d1c951ef08ed24f35129267e3595d86f57f5d3 upstream. As Documentation/kbuild/llvm.rst implies, building the kernel with a full set of LLVM tools gets very verbose and unwieldy. Provide a single switch LLVM=1 to use Clang and LLVM tools instead of GCC and Binutils. You can pass it from the command line or as an environment variable. Please note LLVM=1 does not turn on the integrated assembler. You need to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the integrated assembler, I think we can make it default. We discussed what we need, and we agreed to go with a simple boolean flag that switches both target and host tools: https://lkml.org/lkml/2020/3/28/494 https://lkml.org/lkml/2020/4/3/43 Some items discussed, but not adopted: - LLVM_DIR When multiple versions of LLVM are installed, I just thought supporting LLVM_DIR=/path/to/my/llvm/bin/ might be useful. CC = $(LLVM_DIR)clang LD = $(LLVM_DIR)ld.lld ... However, we can handle this by modifying PATH. So, we decided to not do this. - LLVM_SUFFIX Some distributions (e.g. Debian) package specific versions of LLVM with naming conventions that use the version as a suffix. CC = clang$(LLVM_SUFFIX) LD = ld.lld(LLVM_SUFFIX) ... will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc., but the suffixed versions in /usr/bin/ are symlinks to binaries in /usr/lib/llvm-#/bin/, so this can also be handled by PATH. Signed-off-by: Masahiro Yamada Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor # build Tested-by: Nick Desaulniers Reviewed-by: Nick Desaulniers Signed-off-by: Nick Desaulniers [nd: conflict in exported vars list from not backporting commit e83b9f55448a ("kbuild: add ability to generate BTF type info for vmlinux")] [nd: hunk against Documentation/kbuild/kbuild.rst dropped due to not backporting commit cd238effefa2 ("docs: kbuild: convert docs to ReST and rename to *.rst")] Signed-off-by: Greg Kroah-Hartman (cherry-picked from commit 62353048e2d4e398cfc22dbee3e1a7f6f535dcc1) Change-Id: Ib62c20d4d01b0b95bdcd5e73fa18f32cdb8f585c --- Documentation/kbuild/kbuild.txt | 5 +++++ Makefile | 22 ++++++++++++++++++++-- 2 files changed, 25 insertions(+), 2 deletions(-) diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt index 0ff6a466a05b..a6aea8f9a161 100644 --- a/Documentation/kbuild/kbuild.txt +++ b/Documentation/kbuild/kbuild.txt @@ -238,3 +238,8 @@ KBUILD_VMLINUX_MAIN All object files for the main part of vmlinux. KBUILD_VMLINUX_INIT and KBUILD_VMLINUX_MAIN together specify all the object files used to link vmlinux. + +LLVM +---- +If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead +of GCC and GNU binutils to build the kernel. diff --git a/Makefile b/Makefile index 9f99af0bcb39..5b032118442f 100644 --- a/Makefile +++ b/Makefile @@ -301,8 +301,14 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \ else if [ -x /bin/bash ]; then echo /bin/bash; \ else echo sh; fi ; fi) +ifneq ($(LLVM),) +HOSTCC = clang +HOSTCXX = clang++ +else HOSTCC = gcc HOSTCXX = g++ +endif + HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu89 HOSTCXXFLAGS = -O2 @@ -337,16 +343,28 @@ scripts/Kbuild.include: ; include scripts/Kbuild.include # Make variables (CC, etc...) +LDGOLD = $(CROSS_COMPILE)ld.gold +CPP = $(CC) -E +ifneq ($(LLVM),) +CC = clang +LD = ld.lld +AR = llvm-ar +NM = llvm-nm +OBJCOPY = llvm-objcopy +OBJDUMP = llvm-objdump +READELF = llvm-readelf +OBJSIZE = llvm-size +STRIP = llvm-strip +else AS = $(CROSS_COMPILE)as LD = $(CROSS_COMPILE)ld -LDGOLD = $(CROSS_COMPILE)ld.gold CC = $(CROSS_COMPILE)gcc -CPP = $(CC) -E AR = $(CROSS_COMPILE)ar NM = $(CROSS_COMPILE)nm STRIP = $(CROSS_COMPILE)strip OBJCOPY = $(CROSS_COMPILE)objcopy OBJDUMP = $(CROSS_COMPILE)objdump +endif AWK = awk GENKSYMS = scripts/genksyms/genksyms INSTALLKERNEL := installkernel -- 2.20.1