rvemu

rvemu is a fast Linux emulator, which can run statically linked RV64 programs.

Yeah, it's a toy, but a fairly complete and fast one, which is perfect for learning how a JIT emulator works.

Features

1. Faster than QEMU, can achieve native performance in some cases.
2. (Almost*) architecture independent, we've tested it under x86_64.
3. Tiny, and easy to understand.
4. Targeting RV64IMFDC w/ Newlib (only a small subset of syscalls is implemented, adding more).

*Support for new architecture requires handling relocations in src/compile.c, but it's relatively easy. A few lines of code would do.

Usage

make -j
riscv64-unknown-elf-gcc hello.c
./rvemu a.out

rvemu can only run under Linux, and clang needs to be installed to run, as rvemu uses clang to generate jit code.

Showcase

Running Lua 4.0.1

$ ./rvemu bin/lua -v
Lua 4.0.1  Copyright (C) 1994-2000 TeCGraf, PUC-Rio

$ ./rvemu bin/lua test/hello.lua
hello world, from Lua!

Running Java (using PitifulVM)

$ javac tests/Hello.java

$ ./rvemu jvm tests/Hello.class
Hello, World!

Notes

1. rvemu uses clang -O3 to generate highly optimized target code.

2. rvemu uses hardfloat technique to gain more performance, just like NEMU, this actually violates the RISC-V standard, but it produces correct results in most cases, and it's way faster than softfloat.

3. rvemu uses a linear-mapped MMU similar to blink, which is really fast.

Benchmark

All the tests is compiled with riscv64-unknown-elf-gcc -O3 for RISC-V and clang-15 for x86 native, and run on Intel Xeon Platinum 8269CY.

• Test suite: nbench
• Unit: iterations/second

NUMERIC SORT

   rvemu | #######################################################      | 1595.92
    QEMU | ############################                                 | 821.9
  Native | ############################################################ | 1735.89

STRING SORT

   rvemu | ###                                                          | 138.96
    QEMU | #                                                            | 25.24
  Native | ############################################################ | 2680.95

BITFIELD

   rvemu | #########################################################    | 741057761.48
    QEMU | ###############################                              | 406495858.33
  Native | ############################################################ | 783239543.75

FP EMULATION

   rvemu | ##################################                           | 591.06
    QEMU | #########                                                    | 162.26
  Native | ############################################################ | 1040.14

FOURIER

   rvemu | ###                                                          | 6284.49
    QEMU | ##                                                           | 5867.78
  Native | ############################################################ | 147247.94

ASSIGNMENT

   rvemu | ##################################################           | 84.68
    QEMU | ###################                                          | 31.98
  Native | ############################################################ | 102.54

IDEA

   rvemu | #############################################                | 11070.72
    QEMU | #####################                                        | 5234.18
  Native | ############################################################ | 14832.27

HUFFMAN

   rvemu | ############################################################ | 5070.87
    QEMU | ##########################                                   | 2205.89
  Native | ######################################################       | 4599.75

Refs

Inspired by

1. https://github.com/gamozolabs/fuzz_with_emus
2. https://github.com/jart/blink
3. https://github.com/michaeljclark/rv8
4. https://github.com/OpenXiangShan/NEMU