build LLVM RISC-V Toolchain

LLVM RISC-V toolchain support needs to bootstrap GPU RISC-V toolchain. The project demonstrates how both can be build and installed to a common installation directory.

mkdir -p riscv-toolchain
cd riscv-toolchain

mkdir -p  _install
export PATH=`pwd`/_install/bin:$PATH
hash -r

Build and install riscv-gnu-toolchain

gcc, binutils, newlib

git clone --recursive https://github.com/riscv/riscv-gnu-toolchain
pushd riscv-gnu-toolchain
./configure --prefix=`pwd`/../_install --enable-multilib
make -j`nproc`

qemu

make -j`nproc` build-qemu
popd

install qemu with apt-get as an alternative

sudo apt install qemu-user

build LLVM with bootstrapped riscv-gnu-toolchain

git clone --recursive https://github.com/llvm/llvm-project.git riscv-llvm
pushd riscv-llvm
ln -s ../../clang llvm/tools || true
rm -rf _build
mkdir _build
cd _build
enable_projects="clang;clang-tools-extra;lldb;lld;mlir"

cmake -G Ninja -DCMAKE_BUILD_TYPE="Release" \
  -DLLVM_ENABLE_PROJECTS=${enable_projects} \
  -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_ENABLE_LLD=ON \
  -DBUILD_SHARED_LIBS=True -DLLVM_USE_SPLIT_DWARF=True \
  -DLLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING=OFF \
  -DCMAKE_INSTALL_PREFIX="../../_install" \
  -DLLVM_OPTIMIZED_TABLEGEN=True -DLLVM_BUILD_TESTS=False \
  -DDEFAULT_SYSROOT="../../_install/riscv64-unknown-elf" \
  -DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \
  -DLLVM_TARGETS_TO_BUILD="RISCV" \
  ../llvm
cmake --build . --target install
popd

Compile Hello world sanity test your new RISC-V LLVM

discover llvm targets

llvm-objdump --version | grep riscv riscv32 - 32-bit RISC-V riscv64 - 64-bit RISC-V

generate source hello world

cat >hello.c <<END
#include <stdio.h>

int main(){
  printf("Hello RISCV!\n");
  return 0;
}
END

cat >hello.cpp <<END
#include <iostream>

int main()
{
  std::cout << "Hello RISCV c++!" << std::endl;
  return 0;
}
END

compile and execute RISCV elf via qemu

# 32 bit
clang -O -c hello.c --target=riscv32
riscv64-unknown-elf-gcc hello.o -o hello -march=rv32imac -mabi=ilp32
qemu-riscv32 hello

# 64 bit
clang -O -c hello.c --target=riscv64
riscv64-unknown-elf-gcc hello.o -o hello -march=rv64imac -mabi=lp64
qemu-riscv64 hello

# 32 bit
clang++ -O -c hello.cpp --target=riscv32 --sysroot=_install/riscv64-unknown-elf/ --gcc-toolchain=_install
riscv64-unknown-elf-g++ hello.o -o hello -march=rv32imac -mabi=ilp32
qemu-riscv32 hello

# 64 bit
clang++ -O -c hello.cpp --target=riscv64 --sysroot=_install/riscv64-unknown-elf/ --gcc-toolchain=_install
riscv64-unknown-elf-g++ hello.o -o hello -march=rv64imac -mabi=lp64
qemu-riscv64 hello

Direct execution of RSIC-V binaray on Linux

When running on Linux, the kernel supports a feature called binfmt_misc. This allows for an interpreter to be registered and invoked automatically for a specified binary type. When we installed QEMU, it went ahead and registered our user-mode emulators: ls /proc/sys/fs/binfmt_misc/

Build and run C/C++ source through LLVM IR

_install/bin/clang++ --target=riscv32 prog.cpp -c -emit-llvm -o prog.bc

LLVM IR to Relocatable RISC-V ELF binary

_install/bin/llc -filetype=obj prog.bc -o prog.riscvrel file prog.riscvrel prog.riscvrel: ELF 32-bit LSB relocatable, UCB RISC-V, version 1 (SYSV), not stripped

Perform linking on relocatable RISC-V ELF binary

_install/bin/riscv32-unknown-elf-g++ prog.riscvrel -o prog.riscvexec file prog.riscvexec prog.riscvexec: ELF 32-bit LSB executable, UCB RISC-V, version 1 (SYSV), statically linked, not stripped

running RSIC-V binaray on spike

../riscv-isa-sim/build/bin/spike ../riscv-pk/build/riscv32-unknown-elf/bin/pk prog.riscvexec