Compiling code for the RISC-V

Requirements

• RISC-V Toolchain (32 or 64 bits, in this example I will use the 32 version)
• Here's a guide how to easily build the 32-bits version with the ISA of your choice

Assembler example

riscv32-unknown-elf-as exampleAsm.S -o exampleAsm.o
riscv32-unknown-elf-ld -o exampleAsm.elf -T asm.ld -m elf32lriscv -nostdlib --no-relax

C example

riscv32-unknown-elf-gcc -r exampleC.c -o exampleC.o
riscv32-unknown-elf-ld -o exampleC.elf -T c_prog.ld -m elf32lriscv -nostdlib --no-relax

Trying to use multiplication or other advanced math operations with the rv32I arch? No problem, you just have to declare the path to the correct libgcc library on the loader step.

Watch out!, the path may change depending of how did you setup the multilib, just beware of choosing the libgcc.a corresponding to the rv32I.

riscv32-unknown-elf-ld -o exampleC2.elf -T bram.ld -m elf32lriscv -nostdlib --no-relax /(RVTOOLCHAIN_GCC_LIB_DIR)/libgcc.a

(Optional) Generating .HEX dump (for FPGA)

Alternative 1: use standard tools

riscv32-unknown-elf-objcopy -O binary exampleProg.elf exampleProg.bin
hexdump -e '"%08x\n"' exampleProg.bin > exampleProg.hex

Alternative 2: use elf2hex

• A guide to install the elf2hex tool

riscv32-unknown-elf-elf2hex --bit-width 32 --input exampleProg.elf --output exampleProg.hex