[PATCH v2 1/2] Makefile: Support building with Clang and LLVM binutils
Bin Meng
bmeng.cn at gmail.com
Thu Jul 8 18:50:41 PDT 2021
On Fri, Jul 9, 2021 at 1:51 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> This is intended to mirror the Linux kernel. Building with CC=clang will
> use Clang as the compiler but default to using the existing binutils.
> Building with LLVM=1 will default to using Clang and LLVM binutils.
>
> Whilst GCC will accept the -N linker option and forward it on to the
> linker, Clang will not, and so in order to support both compilers we
> must use -Wl, to forward it to the linker as is required for most other
> linker options.
>
> Signed-off-by: Jessica Clarke <jrtc27 at jrtc27.com>
> ---
> Makefile | 57 +++++++++++++++++++++++++++++++++++++++++++++++++------
> README.md | 39 +++++++++++++++++++++++++++++++++++--
> 2 files changed, 88 insertions(+), 8 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 6b64205..3fe8153 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -76,26 +76,54 @@ OPENSBI_VERSION_MINOR=`grep "define OPENSBI_VERSION_MINOR" $(include_dir)/sbi/sb
> OPENSBI_VERSION_GIT=$(shell if [ -d $(src_dir)/.git ]; then git describe 2> /dev/null; fi)
>
> # Setup compilation commands
> +ifneq ($(LLVM),)
> +CC = clang
> +AR = llvm-ar
> +LD = ld.lld
> +OBJCOPY = llvm-objcopy
> +else
> ifdef CROSS_COMPILE
> CC = $(CROSS_COMPILE)gcc
> -CPP = $(CROSS_COMPILE)cpp
> AR = $(CROSS_COMPILE)ar
> LD = $(CROSS_COMPILE)ld
> OBJCOPY = $(CROSS_COMPILE)objcopy
> else
> CC ?= gcc
> -CPP ?= cpp
> AR ?= ar
> LD ?= ld
> OBJCOPY ?= objcopy
> endif
> +endif
> +CPP = $(CC) -E
> AS = $(CC)
> DTC = dtc
>
> -# Guess the compillers xlen
> -OPENSBI_CC_XLEN := $(shell TMP=`$(CC) -dumpmachine | sed 's/riscv\([0-9][0-9]\).*/\1/'`; echo $${TMP})
> +ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
> +CC_IS_CLANG = y
> +else
> +CC_IS_CLANG = n
> +endif
> +
> +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),)
> +LD_IS_LLD = y
> +else
> +LD_IS_LLD = n
> +endif
> +
> +ifeq ($(CC_IS_CLANG),y)
> +ifneq ($(CROSS_COMPILE),)
> +CLANG_TARGET = -target $(notdir $(CROSS_COMPILE:%-=%))
It's odd that when we use full LLVM toolchains we still need to
specify CROSS_COMPILE in order to only guess the "--target" value.
This can be written directly to --target=riscv64 / riscv32 depending
OPENSBI_CC_XLEN
> +endif
> +endif
> +
> +# Guess the compiler's XLEN
> +OPENSBI_CC_XLEN := $(shell TMP=`$(CC) $(CLANG_TARGET) -dumpmachine | sed 's/riscv\([0-9][0-9]\).*/\1/'`; echo $${TMP})
> +
> +# Guess the compiler's ABI and ISA
> +ifneq ($(CC_IS_CLANG),y)
> OPENSBI_CC_ABI := $(shell TMP=`$(CC) -v 2>&1 | sed -n 's/.*\(with\-abi=\([a-zA-Z0-9]*\)\).*/\2/p'`; echo $${TMP})
> OPENSBI_CC_ISA := $(shell TMP=`$(CC) -v 2>&1 | sed -n 's/.*\(with\-arch=\([a-zA-Z0-9]*\)\).*/\2/p'`; echo $${TMP})
> +endif
>
> # Setup platform XLEN
> ifndef PLATFORM_RISCV_XLEN
> @@ -194,7 +222,11 @@ else
> endif
>
> # Setup compilation commands flags
> -GENFLAGS = -I$(platform_src_dir)/include
> +ifeq ($(CC_IS_CLANG),y)
> +GENFLAGS += $(CLANG_TARGET)
> +GENFLAGS += -Wno-unused-command-line-argument
> +endif
> +GENFLAGS += -I$(platform_src_dir)/include
> GENFLAGS += -I$(include_dir)
> ifneq ($(OPENSBI_VERSION_GIT),)
> GENFLAGS += -DOPENSBI_VERSION_GIT="\"$(OPENSBI_VERSION_GIT)\""
> @@ -208,6 +240,9 @@ CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
> CFLAGS += -mno-save-restore -mstrict-align
> CFLAGS += -mabi=$(PLATFORM_RISCV_ABI) -march=$(PLATFORM_RISCV_ISA)
> CFLAGS += -mcmodel=$(PLATFORM_RISCV_CODE_MODEL)
> +ifeq ($(LD_IS_LLD),y)
> +CFLAGS += -mno-relax
> +endif
> CFLAGS += $(GENFLAGS)
> CFLAGS += $(platform-cflags-y)
> CFLAGS += -fno-pie -no-pie
> @@ -222,18 +257,28 @@ ASFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
> ASFLAGS += -mno-save-restore -mstrict-align
> ASFLAGS += -mabi=$(PLATFORM_RISCV_ABI) -march=$(PLATFORM_RISCV_ISA)
> ASFLAGS += -mcmodel=$(PLATFORM_RISCV_CODE_MODEL)
> +ifeq ($(LD_IS_LLD),y)
> +ASFLAGS += -mno-relax
> +endif
> ASFLAGS += $(GENFLAGS)
> ASFLAGS += $(platform-asflags-y)
> ASFLAGS += $(firmware-asflags-y)
>
> ARFLAGS = rcs
>
> -ELFFLAGS += -Wl,--build-id=none -N -static-libgcc -lgcc
> +ifeq ($(LD_IS_LLD),y)
> +ELFFLAGS += -fuse-ld=lld
> +endif
> +ELFFLAGS += -Wl,--build-id=none -Wl,-N -static-libgcc -lgcc
> ELFFLAGS += $(platform-ldflags-y)
> ELFFLAGS += $(firmware-ldflags-y)
>
> MERGEFLAGS += -r
> +ifeq ($(LD_IS_LLD),y)
> +MERGEFLAGS += -b elf
> +else
> MERGEFLAGS += -b elf$(PLATFORM_RISCV_XLEN)-littleriscv
> +endif
> MERGEFLAGS += -m elf$(PLATFORM_RISCV_XLEN)lriscv
>
> DTSCPPFLAGS = $(CPPFLAGS) -nostdinc -nostdlib -fno-builtin -D__DTS__ -x assembler-with-cpp
> diff --git a/README.md b/README.md
> index 03c02fb..e97dcc4 100644
> --- a/README.md
> +++ b/README.md
> @@ -96,8 +96,13 @@ Required Toolchain
> ------------------
>
> OpenSBI can be compiled natively or cross-compiled on a x86 host. For
> -cross-compilation, you can build your own toolchain or just download
> -a prebuilt one from the [Bootlin toolchain repository].
> +cross-compilation, you can build your own toolchain, download a prebuilt one
> +from the [Bootlin toolchain repository] or install a distribution-provided
> +toolchain; if you opt to use LLVM/Clang, most distribution toolchains will
> +support cross-compiling for RISC-V using the same toolchain as your native
> +LLVM/Clang toolchain due to LLVM's ability to support multiple backends in the
> +same binary, so is often an easy way to obtain a working cross-compilation
> +toolchain.
>
> Please note that only a 64-bit version of the toolchain is available in
> the Bootlin toolchain repository for now.
> @@ -202,6 +207,36 @@ export PLATFORM_RISCV_XLEN=32
>
> will generate 32-bit OpenSBI images. And vice vesa.
>
> +Building with Clang/LLVM
> +------------------------
> +
> +OpenSBI can also be built with Clang/LLVM. To build with just Clang but keep
> +the default binutils (which will still use the *CROSS_COMPILE* prefix if
> +defined), override the *CC* make variable with:
> +```
> +make CC=clang
Testing with the pre-built official LLVM 12 release for Ubuntu 20.04
[1], along with bootlin pre-built cross-compile GCC [2]:
There are 3 build warnings when using the default binutils:
AS platform/generic/firmware/fw_dynamic.o
firmware/fw_base.S:557:2: warning: fw_platform_init changed binding to STB_WEAK
.weak fw_platform_init
^
AS platform/generic/firmware/fw_jump.o
firmware/fw_base.S:557:2: warning: fw_platform_init changed binding to STB_WEAK
.weak fw_platform_init
^
AS platform/generic/firmware/fw_payload.o
firmware/fw_base.S:557:2: warning: fw_platform_init changed binding to STB_WEAK
.weak fw_platform_init
^
And several warnings from the GNU linker:
/share/toolchains/riscv64/bin/riscv64-linux-ld: warning: library
search path "/lib/../lib64" is unsafe for cross-compilation
/share/toolchains/riscv64/bin/riscv64-linux-ld: warning: library
search path "/usr/lib/../lib64" is unsafe for cross-compilation
/share/toolchains/riscv64/bin/riscv64-linux-ld: warning: library
search path "/lib" is unsafe for cross-compilation
/share/toolchains/riscv64/bin/riscv64-linux-ld: warning: library
search path "/usr/lib" is unsafe for cross-compilation
The generated fw_dynamic firmware image does not boot on QEMU 'virt'.
Initial debugging shows that it returns SBI_EINVAL in
sanitize_domain().
> +```
> +
> +To build with a full LLVM-based toolchain, not just Clang, enable the *LLVM*
> +option with:
> +```
> +make LLVM=1
> +```
> +
> +When using Clang, *CROSS_COMPILE* must be defined if the default target for the
> +used Clang is not RISC-V. For Clang, rather than being used as a prefix for the
> +executable name, it will instead be passed via the `-target` option with the
> +trailing `-` removed, so must be a valid triple.
> +
> +These can also be mixed; for example using a GCC cross-compiler but LLVM
> +binutils would be:
> +```
> +make CC=riscv64-unknown-elf-gcc LLVM=1
> +```
> +
> +These variables must be passed for all the make invocations described in this
> +document.
> +
> Contributing to OpenSBI
> -----------------------
[1] https://github.com/llvm/llvm-project/releases/download/llvmorg-12.0.0/clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-20.04.tar.xz
[2] https://toolchains.bootlin.com/downloads/releases/toolchains/riscv64/tarballs/riscv64--glibc--bleeding-edge-2020.08-1.tar.bz2
Regards,
Bin
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