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Makefile: Support building with Clang and LLVM binutils

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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.

Note that there is currently a bug when using Clang as the compiler and
riscv64-linux-gnu-ld as the linker for FW_PIC=y. At first glance this
appears to be a bug in GNU binutils, but this could also be Clang or
OpenSBI at fault in some subtle way. Thus, for now, advise that this
combination be avoided.

Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Tested-by: Anup Patel <anup.patel@wdc.com>
This commit is contained in:
Jessica Clarke
2021-07-11 03:28:23 +01:00
committed by Anup Patel
parent 09ad811ec4
commit 2942777425
2 changed files with 105 additions and 9 deletions
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66
Makefile
View File

@@ -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:%-=%))
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
@@ -106,8 +134,21 @@ ifndef PLATFORM_RISCV_XLEN
endif
endif
ifeq ($(CC_IS_CLANG),y)
ifeq ($(CROSS_COMPILE),)
CLANG_TARGET = --target=riscv$(PLATFORM_RISCV_XLEN)-unknown-elf
endif
endif
ifeq ($(LD_IS_LLD),y)
RELAX_FLAG = -mno-relax
USE_LD_FLAG = -fuse-ld=lld
else
USE_LD_FLAG = -fuse-ld=bfd
endif
# Check whether the linker supports creating PIEs
OPENSBI_LD_PIE := $(shell $(CC) -fPIE -nostdlib -Wl,-pie -x c /dev/null -o /dev/null >/dev/null 2>&1 && echo y || echo n)
OPENSBI_LD_PIE := $(shell $(CC) $(CLANG_TARGET) $(RELAX_FLAG) $(USE_LD_FLAG) -fPIE -nostdlib -Wl,-pie -x c /dev/null -o /dev/null >/dev/null 2>&1 && echo y || echo n)
# Setup list of objects.mk files
ifdef PLATFORM
@@ -197,7 +238,11 @@ else
endif
# Setup compilation commands flags
GENFLAGS = -I$(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="\"$(OPENSBI_VERSION_GIT)\""
@@ -211,6 +256,7 @@ CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
CFLAGS += -mno-save-restore -mstrict-align
CFLAGS += -mabi=$(PLATFORM_RISCV_ABI) -march=$(PLATFORM_RISCV_ISA)
CFLAGS += -mcmodel=$(PLATFORM_RISCV_CODE_MODEL)
CFLAGS += $(RELAX_FLAG)
CFLAGS += $(GENFLAGS)
CFLAGS += $(platform-cflags-y)
CFLAGS += -fno-pie -no-pie
@@ -225,18 +271,24 @@ ASFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
ASFLAGS += -mno-save-restore -mstrict-align
ASFLAGS += -mabi=$(PLATFORM_RISCV_ABI) -march=$(PLATFORM_RISCV_ISA)
ASFLAGS += -mcmodel=$(PLATFORM_RISCV_CODE_MODEL)
ASFLAGS += $(RELAX_FLAG)
ASFLAGS += $(GENFLAGS)
ASFLAGS += $(platform-asflags-y)
ASFLAGS += $(firmware-asflags-y)
ARFLAGS = rcs
ELFFLAGS += -Wl,--build-id=none -N -static-libgcc -lgcc
ELFFLAGS += $(USE_LD_FLAG)
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

48
README.md
View File

@@ -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 +207,45 @@ 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
```
To build with a full LLVM-based toolchain, not just Clang, enable the *LLVM*
option with:
```
make LLVM=1
```
When using Clang, *CROSS_COMPILE* often does not need to be defined unless
using GNU binutils with prefixed binary names. *PLATFORM_RISCV_XLEN* will be
used to infer a default triple to pass to Clang, so if *PLATFORM_RISCV_XLEN*
itself defaults to an undesired value then prefer setting that rather than the
full triple via *CROSS_COMPILE*. If *CROSS_COMPILE* is nonetheless defined,
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.
NOTE: Using Clang with a `riscv*-linux-gnu` GNU binutils linker has been seen
to produce broken binaries with missing relocations; it is therefore currently
recommended that this combination be avoided or *FW_PIC=n* be used to disable
building OpenSBI as a position-independent binary.
Contributing to OpenSBI
-----------------------