[PATCH 1/2] Makefile: Support building with Clang and LLVM binutils

[Jessica Clarke]

On 5 Jul 2021, at 14:05, Bin Meng <bmeng.cn at gmail.com> wrote:
> 
> On Sun, Jul 4, 2021 at 1:56 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.
>> 
>> Note that the ifdef CROSS_COMPILE is removed, since it served little
>> purpose. Variables assigned with = are still overridable on the command
>> line, the only difference compared with ?= is whether environment
>> variables also override them, but that's not something Kbuild-using
>> projects usually support (at least Linux and U-Boot both unconditionally
>> use = like this now does).
>> 
> 
> Please update the documentation for how to use LLVM to build as well.
> 
>> Signed-off-by: Jessica Clarke <jrtc27 at jrtc27.com>
>> ---
>> Makefile | 59 ++++++++++++++++++++++++++++++++++++++++++++------------
>> 1 file changed, 47 insertions(+), 12 deletions(-)
>> 
>> diff --git a/Makefile b/Makefile
>> index 6b64205..40bcab6 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -76,26 +76,47 @@ OPENSBI_VERSION_MINOR=`grep "define OPENSBI_VERSION_MINOR" $(include_dir)/sbi/sb
>> OPENSBI_VERSION_GIT=$(shell if [ -d $(src_dir)/.git ]; then git describe 2> /dev/null; fi)
>> 
>> # Setup compilation commands
>> -ifdef CROSS_COMPILE
>> +ifneq ($(LLVM),)
>> +CC             =       clang
>> +AR             =       llvm-ar
>> +LD             =       ld.lld
>> +OBJCOPY                =       llvm-objcopy
>> +else
>> 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
>> +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:%-=%))
>> +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 +215,11 @@ 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="\"$(OPENSBI_VERSION_GIT)\""
>> @@ -208,6 +233,9 @@ CFLAGS              +=      -fno-omit-frame-pointer -fno-optimize-sibling-calls
>> CFLAGS         +=      -mno-save-restore -mstrict-align
>> CFLAGS         +=      -mabi=$(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         +=      $(platform-cflags-y)
>> CFLAGS         +=      -fno-pie -no-pie
>> @@ -222,18 +250,25 @@ ASFLAGS           +=      -fno-omit-frame-pointer -fno-optimize-sibling-calls
>> ASFLAGS                +=      -mno-save-restore -mstrict-align
>> ASFLAGS                +=      -mabi=$(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
>> +ELFFLAGS       +=      -Wl,--build-id=none -Wl,-N -static-libgcc -lgcc
> 
> This looks like an irrelevant bug fix?

No; GCC will forward -N to the linker despite it being a linker-only
option, Clang requires it to be manually forwarded with -Wl.

Jess