Introduce unreachable_instruction_enabled option (#3)

crates/wasm-smith/src/config.rs

@@ -474,6 +474,14 @@ pub trait Config: 'static + std::fmt::Debug {
     fn call_indirect_enabled(&self) -> bool {
         true
     }
+
+    /// Determines whether `unreachable` instruction is enabled
+    /// in the generating module.
+    ///
+    /// Defaults to `true`.
+    fn unreachable_instruction_enabled(&self) -> bool {
+        true
+    }
 }
 
 /// The default configuration.
@@ -551,6 +559,7 @@ pub struct SwarmConfig {
     pub table_max_size_required: bool,
     pub memory_grow_enabled: bool,
     pub call_indirect_enabled: bool,
+    pub unreachable_instruction_enabled: bool,
 }
 
 impl<'a> Arbitrary<'a> for SwarmConfig {
@@ -598,6 +607,7 @@ impl<'a> Arbitrary<'a> for SwarmConfig {
             float_enabled: u.arbitrary()?,
             memory_grow_enabled: u.arbitrary()?,
             call_indirect_enabled: u.arbitrary()?,
+            unreachable_instruction_enabled: u.arbitrary()?,
 
             // These fields, unlike the ones above, are less useful to set.
             // They either make weird inputs or are for features not widely
@@ -838,4 +848,8 @@ impl Config for SwarmConfig {
     fn call_indirect_enabled(&self) -> bool {
         self.call_indirect_enabled
     }
+
+    fn unreachable_instruction_enabled(&self) -> bool {
+        self.unreachable_instruction_enabled
+    }
 }

crates/wasm-smith/src/core/code_builder.rs

@@ -87,7 +87,7 @@ macro_rules! instructions {
 //    less than 1000.
 instructions! {
     // Control instructions.
-    (None, unreachable, Control, 990),
+    (Some(unreachable_valid), unreachable, Control, 990),
     (None, nop, Control, 800),
     (None, block, Control),
     (None, r#loop, Control),
@@ -1099,6 +1099,11 @@ fn arbitrary_val(ty: ValType, u: &mut Unstructured<'_>) -> Instruction {
     }
 }
 
+#[inline]
+fn unreachable_valid(module: &Module, _: &mut CodeBuilder) -> bool {
+    module.config.unreachable_instruction_enabled()
+}
+
 fn unreachable(_: &mut Unstructured, _: &Module, _: &mut CodeBuilder) -> Result<Instruction> {
     Ok(Instruction::Unreachable)
 }