1 //! Evaluate an exported Wasm function using the WebAssembly specification
2 //! reference interpreter.
3 
4 use crate::generators::{Config, DiffValue, DiffValueType};
5 use crate::oracles::engine::{DiffEngine, DiffInstance};
6 use anyhow::{Error, Result, anyhow};
7 use wasm_spec_interpreter::SpecValue;
8 use wasmtime::Trap;
9 
10 /// A wrapper for `wasm-spec-interpreter` as a [`DiffEngine`].
11 pub struct SpecInterpreter;
12 
13 impl SpecInterpreter {
14     pub(crate) fn new(config: &mut Config) -> Self {
15         let config = &mut config.module_config.config;
16 
17         config.min_memories = config.min_memories.min(1);
18         config.max_memories = config.max_memories.min(1);
19         config.min_tables = config.min_tables.min(1);
20         config.max_tables = config.max_tables.min(1);
21 
22         config.memory64_enabled = false;
23         config.threads_enabled = false;
24         config.bulk_memory_enabled = false;
25         config.reference_types_enabled = false;
26         config.tail_call_enabled = false;
27         config.relaxed_simd_enabled = false;
28         config.custom_page_sizes_enabled = false;
29         config.wide_arithmetic_enabled = false;
30         config.extended_const_enabled = false;
31         config.exceptions_enabled = false;
32 
33         Self
34     }
35 }
36 
37 impl DiffEngine for SpecInterpreter {
38     fn name(&self) -> &'static str {
39         "spec"
40     }
41 
42     fn instantiate(&mut self, wasm: &[u8]) -> Result<Box<dyn DiffInstance>> {
43         let instance = wasm_spec_interpreter::instantiate(wasm)
44             .map_err(|e| anyhow!("failed to instantiate in spec interpreter: {e}"))?;
45         Ok(Box::new(SpecInstance { instance }))
46     }
47 
48     fn assert_error_match(&self, err: &Error, trap: &Trap) {
49         // TODO: implement this for the spec interpreter
50         let _ = (trap, err);
51     }
52 
53     fn is_non_deterministic_error(&self, err: &Error) -> bool {
54         err.to_string().contains("(Isabelle) call stack exhausted")
55     }
56 }
57 
58 struct SpecInstance {
59     instance: wasm_spec_interpreter::SpecInstance,
60 }
61 
62 impl DiffInstance for SpecInstance {
63     fn name(&self) -> &'static str {
64         "spec"
65     }
66 
67     fn evaluate(
68         &mut self,
69         function_name: &str,
70         arguments: &[DiffValue],
71         _results: &[DiffValueType],
72     ) -> Result<Option<Vec<DiffValue>>> {
73         let arguments = arguments.iter().map(SpecValue::from).collect();
74         match wasm_spec_interpreter::interpret(&self.instance, function_name, Some(arguments)) {
75             Ok(results) => Ok(Some(results.into_iter().map(SpecValue::into).collect())),
76             Err(err) => Err(anyhow!(err)),
77         }
78     }
79 
80     fn get_global(&mut self, name: &str, _ty: DiffValueType) -> Option<DiffValue> {
81         use wasm_spec_interpreter::{SpecExport::Global, export};
82         if let Ok(Global(g)) = export(&self.instance, name) {
83             Some(g.into())
84         } else {
85             panic!("expected an exported global value at name `{name}`")
86         }
87     }
88 
89     fn get_memory(&mut self, name: &str, _shared: bool) -> Option<Vec<u8>> {
90         use wasm_spec_interpreter::{SpecExport::Memory, export};
91         if let Ok(Memory(m)) = export(&self.instance, name) {
92             Some(m)
93         } else {
94             panic!("expected an exported memory at name `{name}`")
95         }
96     }
97 }
98 
99 impl From<&DiffValue> for SpecValue {
100     fn from(v: &DiffValue) -> Self {
101         match *v {
102             DiffValue::I32(n) => SpecValue::I32(n),
103             DiffValue::I64(n) => SpecValue::I64(n),
104             DiffValue::F32(n) => SpecValue::F32(n as i32),
105             DiffValue::F64(n) => SpecValue::F64(n as i64),
106             DiffValue::V128(n) => SpecValue::V128(n.to_le_bytes().to_vec()),
107             DiffValue::FuncRef { .. }
108             | DiffValue::ExternRef { .. }
109             | DiffValue::AnyRef { .. }
110             | DiffValue::ExnRef { .. }
111             | DiffValue::ContRef { .. } => {
112                 unimplemented!()
113             }
114         }
115     }
116 }
117 
118 impl From<SpecValue> for DiffValue {
119     fn from(spec: SpecValue) -> DiffValue {
120         match spec {
121             SpecValue::I32(n) => DiffValue::I32(n),
122             SpecValue::I64(n) => DiffValue::I64(n),
123             SpecValue::F32(n) => DiffValue::F32(n as u32),
124             SpecValue::F64(n) => DiffValue::F64(n as u64),
125             SpecValue::V128(n) => {
126                 assert_eq!(n.len(), 16);
127                 DiffValue::V128(u128::from_le_bytes(n.as_slice().try_into().unwrap()))
128             }
129         }
130     }
131 }
132 
133 /// Set up the OCaml runtime for triggering its signal handler configuration.
134 ///
135 /// Because both the OCaml runtime and Wasmtime set up signal handlers, we must
136 /// carefully decide when to instantiate them; this function allows us to
137 /// control when. Wasmtime uses these signal handlers for catching various
138 /// WebAssembly failures. On certain OSes (e.g. Linux `x86_64`), the signal
139 /// handlers interfere, observable as an uncaught `SIGSEGV`--not even caught by
140 /// libFuzzer.
141 ///
142 /// This failure can be mitigated by always running Wasmtime second in
143 /// differential fuzzing. In some cases, however, this is not possible because
144 /// which engine will execute first is unknown. This function can be explicitly
145 /// executed first, e.g., during global initialization, to avoid this issue.
146 pub fn setup_ocaml_runtime() {
147     wasm_spec_interpreter::setup_ocaml_runtime();
148 }
149 
150 #[cfg(test)]
151 mod tests {
152     use super::*;
153 
154     #[test]
155     fn smoke() {
156         if !wasm_spec_interpreter::support_compiled_in() {
157             return;
158         }
159         crate::oracles::engine::smoke_test_engine(|_, config| Ok(SpecInterpreter::new(config)))
160     }
161 }
162