1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151

//! A WebAssembly test case generator.
//!
//! ## Usage
//!
//! First, use [`cargo fuzz`](https://github.com/rust-fuzz/cargo-fuzz) to define
//! a new fuzz target:
//!
//! ```shell
//! $ cargo fuzz add my_wasm_smith_fuzz_target
//! ```
//!
//! Next, add `wasm-smith` to your dependencies:
//!
//! ```toml
//! # fuzz/Cargo.toml
//!
//! [dependencies]
//! wasm-smith = "0.4.0"
//! ```
//!
//! Then, define your fuzz target so that it takes arbitrary
//! `wasm_smith::Module`s as an argument, convert the module into serialized
//! Wasm bytes via the `to_bytes` method, and then feed it into your system:
//!
//! ```no_run
//! // fuzz/fuzz_targets/my_wasm_smith_fuzz_target.rs
//!
//! #![no_main]
//!
//! use libfuzzer_sys::fuzz_target;
//! use wasm_smith::Module;
//!
//! fuzz_target!(|module: Module| {
//!     let wasm_bytes = module.to_bytes();
//!
//!     // Your code here...
//! });
//! ```
//!
//! Finally, start fuzzing:
//!
//! ```shell
//! $ cargo fuzz run my_wasm_smith_fuzz_target
//! ```
//!
//! > **Note:** For a real world example, also check out [the `validate` fuzz
//! > target](https://github.com/fitzgen/wasm-smith/blob/main/fuzz/fuzz_targets/validate.rs)
//! > defined in this repository. Using the `wasmparser` crate, it checks that
//! > every module generated by `wasm-smith` validates successfully.
//!
//! ## Design
//!
//! The design and implementation strategy of wasm-smith is outlined in
//! [this article](https://fitzgeraldnick.com/2020/08/24/writing-a-test-case-generator.html).

#![deny(missing_docs, missing_debug_implementations)]
// Needed for the `instructions!` macro in `src/code_builder.rs`.
#![recursion_limit = "512"]

mod component;
mod config;
mod core;

pub use crate::core::{
    ConfiguredModule, InstructionKind, InstructionKinds, MaybeInvalidModule, Module,
};
use arbitrary::{Result, Unstructured};
pub use component::{Component, ConfiguredComponent};
pub use config::{Config, DefaultConfig, SwarmConfig};

use std::{collections::HashSet, str};

/// Do something an arbitrary number of times.
///
/// The callback can return `false` to exit the loop early.
pub(crate) fn arbitrary_loop<'a>(
    u: &mut Unstructured<'a>,
    min: usize,
    max: usize,
    mut f: impl FnMut(&mut Unstructured<'a>) -> Result<bool>,
) -> Result<()> {
    assert!(max >= min);
    for _ in 0..min {
        if !f(u)? {
            break;
        }
    }
    for _ in 0..(max - min) {
        let keep_going = u.arbitrary().unwrap_or(false);
        if !keep_going {
            break;
        }

        if !f(u)? {
            break;
        }
    }

    Ok(())
}

// Mirror what happens in `Arbitrary for String`, but do so with a clamped size.
pub(crate) fn limited_str<'a>(max_size: usize, u: &mut Unstructured<'a>) -> Result<&'a str> {
    let size = u.arbitrary_len::<u8>()?;
    let size = std::cmp::min(size, max_size);
    match str::from_utf8(&u.peek_bytes(size).unwrap()) {
        Ok(s) => {
            u.bytes(size).unwrap();
            Ok(s.into())
        }
        Err(e) => {
            let i = e.valid_up_to();
            let valid = u.bytes(i).unwrap();
            let s = unsafe {
                debug_assert!(str::from_utf8(valid).is_ok());
                str::from_utf8_unchecked(valid)
            };
            Ok(s)
        }
    }
}

pub(crate) fn limited_string(max_size: usize, u: &mut Unstructured) -> Result<String> {
    Ok(limited_str(max_size, u)?.into())
}

pub(crate) fn unique_string(
    max_size: usize,
    names: &mut HashSet<String>,
    u: &mut Unstructured,
) -> Result<String> {
    let mut name = limited_string(max_size, u)?;
    while names.contains(&name) {
        name.push_str(&format!("{}", names.len()));
    }
    names.insert(name.clone());
    Ok(name)
}

pub(crate) fn unique_non_empty_string(
    max_size: usize,
    names: &mut HashSet<String>,
    u: &mut Unstructured,
) -> Result<String> {
    let mut s = unique_string(max_size, names, u)?;
    while s.is_empty() || names.contains(&s) {
        use std::fmt::Write;
        write!(&mut s, "{}", names.len()).unwrap();
    }
    Ok(s)
}