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

[Jessica Clarke]

On 5 Jul 2021, at 14:11, Bin Meng <bmeng.cn at gmail.com> wrote:
> 
> 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.

That seems like unnecessary busywork. It’s a one-line change that’s
needed to support Clang, and not needed when you only support GCC,
therefore I don’t see why it should be separate from all the other
changes in the same file needed to support Clang/LLVM. I mean, if it’s
a requirement to get the patch accepted then I’ll do it, but it seems
highly inconsistent and a waste of my time.

Jess