In order to build the cross toolchain, first install all needed software packages. Additional dependencies will be downloaded and installed during the build process.
sudo apt-get update
sudo apt-get install flex \
bison \
libgmp3-dev \
libmpfr-dev \
autoconf \
texinfo \
build-essential \
libncurses5-dev
A simple process would be using the Makefile passing the architecture and the gcc version available as in:
make riscv32_9.3
Alternativelly, the riscv/build_riscv32_toolchain script will automate the whole process of downloading, configuring and building basic binary tools and the compiler. All we need to do is create a working directory and copy the build script before starting the whole process.
mkdir -p riscv-tools && cd riscv-tools
../riscv/build_riscv32_toolchain_9_3 .
We need permissions to execute the build script. If not set, change the execute bit of the script:
chmod +x build_riscv32_toolchain_9_3
And now we are ready to build the cross toolchain. All software packages will be downloaded (binutils, GCC), unpacked and built. Note that we don't need root permissions to do perform this step.
./build_riscv32_toolchain_9_3
The process takes between 15 minutes to 1 hour, depending on your host machine. After the process completes, you can check if the new compiler and tools were built:
ls riscv32-unknown-elf/gcc-9.3.0/bin/
If among other files, the riscv32-unknown-elf-gcc executable is present, the toolchain was built successfully.
The tools can be installed in any directory. Most of the time, the toolchain can be shared among users, so it makes sense to install the toolchain in the /usr/local directory. To install, just move the risc32-unknown-elf directory the its place. We need root permissions for this step. We will also create a symbolic link to the toolchain so we can keep multiple versions of the same tools in the system.
sudo mv riscv32-unknown-elf /usr/local
cd /usr/local/riscv32-unknown-elf
sudo ln -s gcc-9.3.0 gcc
One last step is to update the PATH environment variable. This can be done in the current terminal or we can update the .bashrc script found in the home directory of the current user.
cd ~
echo "export PATH=$PATH:/usr/local/riscv32-unknown-elf/gcc/bin" >> .bashrc
source .bashrc
To test the toolchain,
riscv32-unknown-elf-gcc -v
Using built-in specs.
COLLECT_GCC=riscv32-unknown-elf-gcc COLLECT_LTO_WRAPPER=/usr/local/riscv32-unknown-elf/gcc-9.3.0/bin/../libexec/gcc/riscv32-unknown-elf/9.3.0/lto-wrapper
Target: riscv32-unknown-elf
Configured with: /home/sergio/Downloads/tools/riscv-toolchain/source/gcc-9.3.0/configure --prefix=/home/sergio/Downloads/tools/riscv-toolchain/riscv32-unknown-elf/gcc-9.3.0 --target=riscv32-unknown-elf --disable-shared --disable-threads --enable-tls --enable-languages=c,c++ --with-newlib --disable-libmudflap --disable-libssp --disable-libquadmath --disable-libgomp --disable-nls --disable-multilibs
Thread model: single
gcc version 9.3.0 (GCC)
If something along this lines is printed, we are all set.