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

[Bin Meng]

On Mon, Jul 5, 2021 at 9:09 PM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> 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.

Thanks for the clarification. I suggest we create a separate patch for
this change.

Regards,
Bin