kbuild: support LLVM=1 to switch the default tools to Clang/LLVM
commit a0d1c951ef
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 <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
parent
c7d8f67db1
commit
62353048e2
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@ -262,3 +262,8 @@ KBUILD_BUILD_USER, KBUILD_BUILD_HOST
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These two variables allow to override the user@host string displayed during
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These two variables allow to override the user@host string displayed during
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boot and in /proc/version. The default value is the output of the commands
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boot and in /proc/version. The default value is the output of the commands
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whoami and host, respectively.
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whoami and host, respectively.
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LLVM
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----
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If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
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of GCC and GNU binutils to build the kernel.
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@ -47,8 +47,12 @@ example:
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LLVM Utilities
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LLVM Utilities
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--------------
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--------------
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LLVM has substitutes for GNU binutils utilities. These can be invoked as
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LLVM has substitutes for GNU binutils utilities. Kbuild supports `LLVM=1`
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additional parameters to `make`.
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to enable them.
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make LLVM=1
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They can be enabled individually. The full list of the parameters:
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make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
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make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
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OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
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OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
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29
Makefile
29
Makefile
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@ -394,8 +394,13 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS 2>/dev/null)
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HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
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HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
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HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
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HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
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HOSTCC = gcc
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ifneq ($(LLVM),)
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HOSTCXX = g++
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HOSTCC = clang
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HOSTCXX = clang++
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else
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HOSTCC = gcc
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HOSTCXX = g++
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endif
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KBUILD_HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
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KBUILD_HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
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-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \
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-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \
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$(HOSTCFLAGS)
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$(HOSTCFLAGS)
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@ -404,16 +409,28 @@ KBUILD_HOSTLDFLAGS := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
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KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
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KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
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# Make variables (CC, etc...)
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# Make variables (CC, etc...)
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LD = $(CROSS_COMPILE)ld
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CC = $(CROSS_COMPILE)gcc
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CPP = $(CC) -E
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CPP = $(CC) -E
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ifneq ($(LLVM),)
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CC = clang
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LD = ld.lld
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AR = llvm-ar
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NM = llvm-nm
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OBJCOPY = llvm-objcopy
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OBJDUMP = llvm-objdump
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READELF = llvm-readelf
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OBJSIZE = llvm-size
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STRIP = llvm-strip
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else
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CC = $(CROSS_COMPILE)gcc
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LD = $(CROSS_COMPILE)ld
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AR = $(CROSS_COMPILE)ar
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AR = $(CROSS_COMPILE)ar
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NM = $(CROSS_COMPILE)nm
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NM = $(CROSS_COMPILE)nm
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STRIP = $(CROSS_COMPILE)strip
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OBJCOPY = $(CROSS_COMPILE)objcopy
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OBJCOPY = $(CROSS_COMPILE)objcopy
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OBJDUMP = $(CROSS_COMPILE)objdump
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OBJDUMP = $(CROSS_COMPILE)objdump
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OBJSIZE = $(CROSS_COMPILE)size
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READELF = $(CROSS_COMPILE)readelf
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READELF = $(CROSS_COMPILE)readelf
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OBJSIZE = $(CROSS_COMPILE)size
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STRIP = $(CROSS_COMPILE)strip
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endif
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PAHOLE = pahole
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PAHOLE = pahole
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LEX = flex
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LEX = flex
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YACC = bison
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YACC = bison
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@ -3,9 +3,15 @@ include ../scripts/Makefile.include
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include ../scripts/Makefile.arch
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include ../scripts/Makefile.arch
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# always use the host compiler
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# always use the host compiler
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ifneq ($(LLVM),)
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HOSTAR ?= llvm-ar
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HOSTCC ?= clang
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HOSTLD ?= ld.lld
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else
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HOSTAR ?= ar
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HOSTAR ?= ar
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HOSTCC ?= gcc
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HOSTCC ?= gcc
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HOSTLD ?= ld
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HOSTLD ?= ld
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endif
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AR = $(HOSTAR)
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AR = $(HOSTAR)
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CC = $(HOSTCC)
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CC = $(HOSTCC)
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LD = $(HOSTLD)
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LD = $(HOSTLD)
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