From 5bcc7d3a325be2394f31cf34ea54d0c9c3dcd995 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 Signed-off-by: Greg Kroah-Hartman Change-Id: I8e0a6f5a8f240752e6f49b31d92669821a2d6e4a --- Documentation/kbuild/kbuild.txt | 5 +++++ Documentation/kbuild/llvm.rst | 8 ++++++-- Makefile | 24 ++++++++++++++++++++---- tools/objtool/Makefile | 6 ++++++ 4 files changed, 37 insertions(+), 6 deletions(-) diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt index 82afdb7f0816..9d80df7f3d81 100755 --- a/Documentation/kbuild/kbuild.txt +++ b/Documentation/kbuild/kbuild.txt @@ -233,3 +233,8 @@ KBUILD_VMLINUX_LIBS All .a "lib" files for vmlinux. KBUILD_VMLINUX_INIT, KBUILD_VMLINUX_MAIN, and KBUILD_VMLINUX_LIBS 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/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index 450708534860..c776b6eee969 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -47,8 +47,12 @@ example: LLVM Utilities -------------- -LLVM has substitutes for GNU binutils utilities. These can be invoked as -additional parameters to `make`. +LLVM has substitutes for GNU binutils utilities. Kbuild supports `LLVM=1` +to enable them. + + make LLVM=1 + +They can be enabled individually. The full list of the parameters: make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\ OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\ diff --git a/Makefile b/Makefile index 7935516c0825..85e6a501ade4 100755 --- a/Makefile +++ b/Makefile @@ -361,8 +361,13 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS 2>/dev/null) HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null) HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null) -HOSTCC = gcc -HOSTCXX = g++ +ifneq ($(LLVM),) +HOSTCC = clang +HOSTCXX = clang++ +else +HOSTCC = gcc +HOSTCXX = g++ +endif HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \ -fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) HOSTCXXFLAGS := -O2 $(HOST_LFS_CFLAGS) @@ -375,16 +380,27 @@ HOSTCFLAGS += -Wno-unused-value -Wno-unused-parameter \ endif # Make variables (CC, etc...) -LD = $(CROSS_COMPILE)ld +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 +STRIP = llvm-strip +else CC = $(CROSS_COMPILE)gcc +LD = $(CROSS_COMPILE)ld LDGOLD = $(CROSS_COMPILE)ld.gold -CPP = $(CC) -E AR = $(CROSS_COMPILE)ar NM = $(CROSS_COMPILE)nm STRIP = $(CROSS_COMPILE)strip OBJCOPY = $(CROSS_COMPILE)objcopy OBJDUMP = $(CROSS_COMPILE)objdump READELF = $(CROSS_COMPILE)readelf +endif AWK = awk GENKSYMS = scripts/genksyms/genksyms INSTALLKERNEL := installkernel diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile index 7786bce816c9..b26a2d62693c 100755 --- a/tools/objtool/Makefile +++ b/tools/objtool/Makefile @@ -7,9 +7,15 @@ ARCH := x86 endif # always use the host compiler +ifneq ($(LLVM),) +HOSTAR ?= llvm-ar +HOSTCC ?= clang +HOSTLD ?= ld.lld +else HOSTAR ?= ar HOSTCC ?= gcc HOSTLD ?= ld +endif AR = $(HOSTAR) CC = $(HOSTCC) LD = $(HOSTLD)