On Tue, Apr 7, 2020 at 11:44 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > 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_IA=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 <masahiroy@xxxxxxxxxx> > Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> # build > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Thanks for the series! Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > > Changes in v2: > - Switch host compilers as well as requested > > Documentation/kbuild/kbuild.rst | 5 +++++ > Documentation/kbuild/llvm.rst | 8 ++++++-- > Makefile | 29 +++++++++++++++++++++++------ > tools/objtool/Makefile | 6 ++++++ > 4 files changed, 40 insertions(+), 8 deletions(-) > > diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst > index 510f38d7e78a..2d1fc03d346e 100644 > --- a/Documentation/kbuild/kbuild.rst > +++ b/Documentation/kbuild/kbuild.rst > @@ -262,3 +262,8 @@ KBUILD_BUILD_USER, KBUILD_BUILD_HOST > These two variables allow to override the user@host string displayed during > boot and in /proc/version. The default value is the output of the commands > whoami and host, respectively. > + > +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 2b40afa58049..81f915c02c4c 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 f9beb696d6d3..ffc1d2c618a7 100644 > --- a/Makefile > +++ b/Makefile > @@ -399,8 +399,13 @@ 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 > KBUILD_HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \ > -fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \ > $(HOSTCFLAGS) > @@ -409,16 +414,28 @@ KBUILD_HOSTLDFLAGS := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS) > KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS) > > # Make variables (CC, etc...) > -LD = $(CROSS_COMPILE)ld > -CC = $(CROSS_COMPILE)gcc > 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 > +CC = $(CROSS_COMPILE)gcc > +LD = $(CROSS_COMPILE)ld > AR = $(CROSS_COMPILE)ar > NM = $(CROSS_COMPILE)nm > -STRIP = $(CROSS_COMPILE)strip > OBJCOPY = $(CROSS_COMPILE)objcopy > OBJDUMP = $(CROSS_COMPILE)objdump > -OBJSIZE = $(CROSS_COMPILE)size > READELF = $(CROSS_COMPILE)readelf > +OBJSIZE = $(CROSS_COMPILE)size > +STRIP = $(CROSS_COMPILE)strip > +endif > PAHOLE = pahole > LEX = flex > YACC = bison > diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile > index ee08aeff30a1..f591c4d1b6fe 100644 > --- a/tools/objtool/Makefile > +++ b/tools/objtool/Makefile > @@ -3,9 +3,15 @@ include ../scripts/Makefile.include > include ../scripts/Makefile.arch > > # always use the host compiler > +ifneq ($(LLVM),) > +HOSTAR ?= llvm-ar > +HOSTCC ?= clang > +HOSTLD ?= ld.lld > +else > HOSTAR ?= ar > HOSTCC ?= gcc > HOSTLD ?= ld > +endif > AR = $(HOSTAR) > CC = $(HOSTCC) > LD = $(HOSTLD) > -- -- Thanks, ~Nick Desaulniers
