C2RARS: A solution to solve the problem of C to RISC-V in RARS

Warning : The project is still in an early stage. But it is already possible to do the conversion of simple programs. Such like your lab assignments in OJ.

The project is of narrow use unless you are mad in debugging RISC-V assembly code in RARS. It is a simple solution to convert C code to RISC-V assembly code that can run in RARS.

Usage

Firstly, you should install riscv64-unknown-elf-gcc. You can install it by the following command in Ubuntu:

sudo apt-get install gcc-riscv64-unknown-elf

Or you prefer riscv32-unknown-elf-gcc, you can clone and compile it by the following command(although it could take 1-2 hours):

git clone https://github.com/riscv/riscv-gnu-toolchain
cd riscv-gnu-toolchain
git submodule update --init --recursive
./configure --prefix=/opt/riscv --with-arch=rv32gc --with-abi=ilp32d
sudo make

Go to https://github.com/riscv-collab/riscv-gnu-toolchain to find more information.

If you are using Windows, you are highly recommended to use WSL.

Write your code in C, download and include syscall.h in your code. Remember don't use std library in your code such as printf, scanf, etc. Instead, you need to use the function in syscall.h. At the end of your C code, you should add exit_program() to make sure the program can exit correctly.

Up to now, you can use the following functions:

read_int()

print_int(int value)

read_double()

print_double(double value)

read_str(char *buf, int len)

print_str(char* str)

exit_program()

You can edit syscall.h to customize your own functions.

You can find a simple example in fib.c, which can calculate the Fibonacci number.

Then you can compile your code by the following command:

riscv64-unknown-elf-gcc -S fib.c

or you are using riscv32-unknown-elf-gcc:

riscv32-unknown-elf-gcc -S fib.c

Check the generated fib.s file, which contains the RISC-V assembly code that could directly run in RARS. Wow!

How it works

The toolchain is based on the riscv32-unknown-elf-gcc. It will compile the C code into RISC-V assembly code. The generated assembly code couldn't run in RARS directly. So some modifications need to be done to make it run in RARS.

Since RARS is not supporting the std library, so I replace the function in the std library with the function in syscall.h by inline assembly of ecall.

RARS won't call the main function by default. So I add a start function to call the main function in the C code.