ravel

master	dev

Introduction

ravel is a RISC-V simulator written for the compiler course taught at Shanghai Jiao Tong University, where the students are typically second-year undergraduates at ACM Honers Class. In this course, students are required to implement a toy compiler that turns Mx* (a toy language used in the course) to RISC-V assembly. This simulator is used to test the correctness of the implementation and measure the quality of the optimization.

Getting started

The only prerequisites are CMake (>= 3.10) and a cpp-17 supporting compiler. You can install the simulator with the following commands.

git clone https://github.com/Engineev/ravel.git
cd ravel
mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local/opt  # or any directory you want
make 
make install
export PATH="/usr/local/opt/bin:$PATH"  # optional

The easiest way to start a simulation is to use the OJ mode, that is,

ravel --oj-mode

Under this mode, the simulator takes test.s and builtin.s as the source code, test.in as the input and redirect the program output into test.out. The results (e.g. exit code) of the simulation will still be outputted directly to stdout. This is equivalent to

ravel --input-file=test.in --output-file=test.out test.s builtin.s 

If you'd like to see the instructions being executed, you may pass in command line option --print-instructions, but note that this will slow down the simulation significantly. Also, if --keep-debug-info is passed in, ravel will perform more checks on memory access and will print information like the call stack if an error occurred, which might be helpful.

Support

In short, if the assembly resembles the one generated with the following command,

riscv32-unknown-linux-gnu-gcc -S -std=c99 -fno-section-anchors main.c

where the build of gcc is configured with

./configure --prefix=/opt/riscv --with-arch=rv32ima --with-abi=ilp32

then in most cases it is supported by the simulator. For LLVM users, the command should be

llc --march=riscv32 --mattr=+m main.ll

See this for information on the risc-v toolchain. For detail on supported directives, instructions and libc functions, see this.

Computing the running time

The output of ravel contains a time filed. This is computed in the following way. For each type of instructions, the number of execution is recorded during the interpretation, and time is computed by a weighted summation. The default weights are listed in the following table. You can change the weights by passing in command line options like -wsimple=2. By default, cache is disabled. You may enable it by passing in --enable-cache.

Type	Weight
simple	1
cache	4
mul	4
br	8
div	8
mem	64
libcIO	64
libcMem	function-dependent

Note: Unconditional jumps are viewed as simple instructions, and the weights used in the test are still subject to change.