Rvsym: a small RISC-V symbolic execution engine

Rvsym can execute rv32im RISC-V programs symbolically.

Building

By default, rvsym uses Boolector as the SMT backend. First you need to set up Boolector:

./pkg/smt/setup-boolector.sh

Then you can build

go build ./cmd/rvsym

Alternatively, you may build with dynamic linking to Z3 if it is installed:

go build -tags z3,noboolector ./cmd/rvsym

In order to build the examples you will also need the RISC-V GNU toolchain. Pre-built toolchains are available from SiFive here. After downloading, unpack the tar archive to /opt/riscv (or if you choose another location, point the RISCV environment variable to your installation).

Usage

See the ./examples/basic directory for a number of example programs. Compile with make, and then run the example of your choosing with rvsym example.elf.

For example, here is get_sign.c:

#include "rvsym.h"

int get_sign(int x) {
    if (x == 0)
        return 0;
    else if (x < 0)
        return -1;
    else
        return 1;
}

int main() {
    int a;
    rvsym_mark_bytes(&a, sizeof(a), "a");
    int r = get_sign(a);
    rvsym_exit();
    return r;
}

Now we compile with the RISC-V toolchain and execute the resulting ELF binary with rvsym. It finds three test cases that exercise each path in the get_sign function.

$ make get_sign.elf
$ rvsym get_sign.elf --summary
--- Test case 0: exit at get_sign.c:20 (0x100a4) ---
a[3:0] -> 0x1
---
--- Test case 1: exit at get_sign.c:20 (0x100a4) ---
a[3:0] -> 0x80000001
---
--- Test case 2: exit at get_sign.c:20 (0x100a4) ---
a[3:0] -> 0x0
---
--- Summary ---
Instructions executed: 148
Total paths: 3
Quiet exits: 0
Unsat exits: 0
Normal exits: 3
Failures: 0
---

Rvsym has the following additional options:

Usage:
  rvsym [OPTIONS] EXE

Application Options:
      --time=    Stop execution after a given amount of seconds
  -s, --summary  Show execution summary
      --elf=     ELF debug information file
      --entry=   Program start address (default: 4096)
  -p, --profile= Dump profiling information to file
  -V, --verbose  Show verbose debug information
  -v, --version  Show version information
  -h, --help     Show this help message

Notes

Rvsym runs in Linux mode for ELF files, and bare-metal mode for .hex or .bin files. In Linux mode, Rvsym sets up the stack properly and provides a limited set of system calls, shown below. In bare-metal mode, Rvsym does not do any set-up. In the future bare-metal mode may include support for exceptions and other privileged CPU features.

The following system calls are provided in Linux mode: exit, open, read, write, lseek, close, fstat (does not provide accurate information), brk. These are a minimal set allowing basic memory allocation and file I/O.