[PATCH v2 1/2] Makefile: Support building with Clang and LLVM binutils
Bin Meng
bmeng.cn at gmail.com
Thu Jul 8 20:11:50 PDT 2021
On Fri, Jul 9, 2021 at 10:35 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 9 Jul 2021, at 02:50, Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > 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
>
> Hm, that’s true. To be honest, the fact that OpenSBI defaults to an
> unprefixed GCC is rather dubious, that’ll likely be for either
> riscv64-linux-gnu or riscv64-unknown-freebsd and thus not suitable
> (there can be subtle issues with using the wrong one, though RISC-V is
> more uniform than some other architectures) so should probably grab
> XLEN from the default GCC and then look for riscvXLEN-unknown-elf-gcc
> if CROSS_COMPILE wasn’t specified. I can at least make it do something
> like that for Clang (keep this code for CROSS_COMPILE not empty, then
> add a -target riscvXLEN-unknown-elf after guessing the XLEN if
> CROSS_COMPILE was empty).
I don't think we should over-complicate things. Passing riscv64 /
riscv32 to --target is enough for OpenSBI when building with clang.
>
> >> +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
> > ^
>
> Yeah, those are known. They’re harmless and easy to fix (just delete
> the .globl lines, as the two are mutually exclusive), so I didn’t
> include it as part of this patch series, LLVM 12 just got stricter
> about this as it’s dodgy code.
Please include a patch to fix these warnings as part of this series.
We should not allow any building warnings to happen.
>
> > 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
>
> Hm, indeed, Clang likes to add some host directories to the search
> path, seemingly only for RISC-V. RISC-V’s bare-metal toolchain driver
> is a bit quirky due to all the multilib stuff the GNU world decided to
> introduce so that’s a bug. They should be harmless though given we
> don’t pass -lfoo, when linking in SBI libraries we pass the path.
Is it a bug of clang, or GNU ld? Could you please file a bug report to
get this issue tracked (if there isn't one already), and mentioned in
the commit message?
>
> > The generated fw_dynamic firmware image does not boot on QEMU 'virt'.
> > Initial debugging shows that it returns SBI_EINVAL in
> > sanitize_domain().
>
> My pure LLVM=1-built fw_dynamic binary on FreeBSD boots U-Boot just fine
> (-M virt -m 2048 -nographic -bios fw_dynamic.elf -kernel u-boot), as
> does an LLVM=1 with LD overridden to be GNU ld 2.33.1 (also on FreeBSD)
> so I don’t know what’s going on there. Though I did discover that
> -fuse-ld=bfd is needed for the non-LLD case otherwise Clang won’t pick
> up an ld.bfd intended to override a system LLD. So my guess is that one
> or other of the binaries you downloaded has broken something. Does
> using LLD work? If you tell me exactly what you ran I can try it on a
> Linux machine myself and see if I can reproduce it.
Switching to full LLVM build does not build for me.
ELF platform/generic/firmware/fw_dynamic.elf
ld.lld: error: can't create dynamic relocation R_RISCV_64 against
symbol: _fw_start in readonly segment; recompile object files with
-fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
>>> defined in opensbi/build/platform/generic/firmware/fw_dynamic.elf.ld:8
>>> referenced by fw_base.S:502 (opensbi/firmware/fw_base.S:502)
>>> opensbi/build/platform/generic/firmware/fw_dynamic.o:(.entry+0x3A0)
ld.lld: error: can't create dynamic relocation R_RISCV_64 against
symbol: _fw_reloc_end in readonly segment; recompile object files with
-fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
>>> defined in opensbi/build/platform/generic/firmware/fw_dynamic.elf.ld:92
>>> referenced by fw_base.S:502 (opensbi/firmware/fw_base.S:502)
>>> opensbi/build/platform/generic/firmware/fw_dynamic.o:(.entry+0x3B0)
clang-12: error: linker command failed with exit code 1 (use -v to see
invocation)
make: *** [Makefile:396:
opensbi/build/platform/generic/firmware/fw_dynamic.elf] Error 1
My environment:
Host: Ubuntu 20.04 x86_64
LLVM: 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
GCC: https://toolchains.bootlin.com/downloads/releases/toolchains/riscv64/tarballs/riscv64--glibc--bleeding-edge-2020.08-1.tar.bz2
Both LLVM and GCC are in my $PATH.
$ make CC=clang CROSS_COMPILE=riscv64-linux- PLATFORM=generic
Result: can build, cannot boot
$ make LLVM=1 CROSS_COMPILE=riscv64-linux- PLATFORM=generic
Result: cannot build
Regards,
Bin
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