rvemu: RISC-V Online Emulataor

RISC-V online emulator with WebAssembly generated by Rust. The emulator implements the standard extensions RV64G (RV64IMAFD) and cimplies with the RISC-V specifications.

The online emulator is available here: rvemu.app

Supports the following RISC-V ISAs (RV64G):

• RV64I (v2.1): supports 52/52 instructions (FENCE, ECALL, and EBREAK don't do anything for now)
• RV64M (v2.0): supports 13/13 instructions
• RV64A (v2.0): supports 22/22 instructions (No atomicity for now)
• RV64F (v2.2): supports 30/30 instructions
• RV64D (v2.2): supports 32/32 instructions
• Zifencei (v2.0): supports 1/1 instructions (FENCE.i doesn't do anything for now)
• Zicsr (v2.0): supports 6/6 instructions (no unittests and no atomicity)

NOTE: This project is currently under intensely development. The source code might be changed dramatically. What to do next is:

1. devices interrupt (refers to memlayout.h in xv6)
   1. keyboards
   2. timer
   3. virtio
   4. block devices
2. virtual memory

Usage

The emulator supports the following commands:

• upload: Upload a local RISC-V binary/local RISC-V binaries for an execution on the emulator.
• ls: List the files you uploaded.
• run [file]: Execute a file.
• help: Print all commands you can use.

Build and run on the local browser

The wasm-pack build command generates a pkg directory and makes Rust source code into .wasm binary. It also generates the JavaScript API for using our Rust-generated WebAssembly. The toolchain's supported target is wasm32-unknown-unknown. You need to execute this command whenever you change your Rust code.

$ make rvemu-wasm
// This is the alias of `wasm-pack build lib/rvemu-wasm --out-dir <path-to-rvemu>/public/pkg --target web`.

This command installs dependencies in the node_modules directory. Need npm install --save in the public directory at the first time and whenever you change dependencies in package.json.

$ npm install --save // at the public directory

You can see the website via http://localhost:8000. npm start is the alias of python3 -m http.server so you need Python3 in your environment.

$ npm start // at the public directory

Build and run as a CLI tool

The emulator can be executed as a CLI tool too. You can build it by make rvemu-cli command which is the alias of cargo build --release --manifest-path lib/rvemu-cli/Cargo.toml.

To execute the RISC-V ELF binary, XV6 in the folloing example, you can use --kernel or -k options to specify the kernel image. Note that xv6-kernel.text is an ELF file without headers by the command riscv64-unknown-elf-objcopy -O binary xv6-kernel.text kernel

$ ./target/release/rvemu-cli --kernel examples/xv6-kernel.text

You can see the details of how to use by the help option.

$ ./target/release/rvemu-cli --help
rvemu: RISC-V emulator 0.0.1
Asami Doi <@d0iasm>

USAGE:
    rvemu-cli [FLAGS] --kernel <kernel>

FLAGS:
    -d, --debug      Enables to output debug messages
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -k, --kernel <kernel>    A kernel ELF image without headers

Build RISC-V binary

This emulator starts to execute at the address 0x8000_0000, the start address of DRAM, so you need to extract .text section to execute your binary file on the emulator.

// Make an assembly file from a C file.
$ riscv64-unknown-elf-gcc -S -nostdlib hoge.c
// Make a binary file from an assembly file with start position 0.
$ riscv64-unknown-elf-gcc -Wl,-Ttext=0x80000000 -nostdlib -o hoge hoge.s
// Extract a text section from a binary file.
$ riscv64-unknown-elf-objcopy -O binary --only-section=.text hoge hoge.text

Testing

ISA testing

You can see the binaries for unit testings in riscv/riscv-tests. The following command executes all rv64ua/d/f/i/m-p-* binaries.

$ make test-isa

Testing with WebAssembly

NOTE: This is deprecated bacause I'll delete them in the future. This tests are implemented in the lib/rvemu-wasm/tests directory.

You need to install a Firefox browser, a Chrome browser, or a Safari browser to run the integration testings. A browser can be specified by a --firefox or a --chrome flag.

$ make test-wasm

Analyzing with perf

$ perf record -F99 --call-graph dwarf ./target/release/rvemu-cli -k ./kernel.text
$ perf report

Publish

The site is hosted by a firebase.

$ firebase deploy

Roadmap

Supports "The RISC-V Instruction Set ManualVolume I: Unprivileged ISADocument Version 20191213"

• RV64G ISA
• RV64C ISA

Supports "The RISC-V Instruction Set ManualVolume II: Privileged ArchitectureDocument Version 20190608-Priv-MSU-Ratified"

• Privileged ISA (URET, SRET, MRET, WFI, SFENCE.VMA, HFENCE.BVMA, and HFENCE.GVMA)
• Machine-level CSRs
• Machine-Mode privileged instructions
• Supervisor-level CSRs
• Supervisor instructions
• Page-Based Virtual-Memory System
• User-level CSRs

Dependencies

• rust toolchain (rustup/rustc/cargo/cargo-generate)
• wasm-pack
• npm
  • xterm
  • xterm-addon-fit
• firebase CLI

Resources

Documents

• RISC-V Specifications
• Rust and WebAssembly
• riscv/riscv-sbi-doc
• riscv/riscv-elf-psabi-doc
• riscv/riscv-asm-manual

Implementation of other emulators

• qemu/qemu
• riscv/riscv-isa-sim
• riscv/riscv-angel
• riscv/riscv-ovpsim
• rv8-io/rv8
• TinyEmu
• stephank/rvsim

Helpful tools

• riscv/riscv-tests
• wat2wasm demo
• RISC-V Online Simulator

Articles about this project

• Emulate 32-Bit And 64-Bit RISC-V In Your Browser With Asami’s Open Source rvemu | Gareth Halfacree, Hackster.io
• Emulate 32-Bit and 64-Bit RISC-V in Your Browser with Asami's Open Source rvemu