Exceptions: add basic support for fuzzing. (#11511)

* Enable use of exceptions in our fuzz module generator.

This patch was provided by Alex in #11505; it is thus

Co-authored-by: Alex Crichton <alex@alexcrichton.com>

* Add ExnRef comparison to differential result checking.

---------

Co-authored-by: Alex Crichton <alex@alexcrichton.com>

Author: cfallin

crates/fuzzing/src/generators/config.rs

@@ -662,6 +662,7 @@ impl WasmtimeConfig {
                 config.config.gc_enabled = false;
                 config.config.tail_call_enabled = false;
                 config.config.reference_types_enabled = false;
+                config.config.exceptions_enabled = false;
                 config.function_references_enabled = false;
 
                 // Winch's SIMD implementations require AVX and AVX2.

crates/fuzzing/src/generators/module.rs

@@ -48,7 +48,7 @@ impl<'a> Arbitrary<'a> for ModuleConfig {
         let _ = config.tail_call_enabled;
         let _ = config.extended_const_enabled;
         let _ = config.gc_enabled;
-        config.exceptions_enabled = false;
+        let _ = config.exceptions_enabled;
         config.custom_page_sizes_enabled = u.arbitrary()?;
         config.wide_arithmetic_enabled = u.arbitrary()?;
         config.memory64_enabled = u.ratio(1, 20)?;

crates/fuzzing/src/generators/value.rs

@@ -272,6 +272,7 @@ impl PartialEq for DiffValue {
             (Self::FuncRef { null: a }, Self::FuncRef { null: b }) => a == b,
             (Self::ExternRef { null: a }, Self::ExternRef { null: b }) => a == b,
             (Self::AnyRef { null: a }, Self::AnyRef { null: b }) => a == b,
+            (Self::ExnRef { null: a }, Self::ExnRef { null: b }) => a == b,
             _ => false,
         }
     }

crates/fuzzing/src/oracles.rs

@@ -1417,7 +1417,8 @@ mod tests {
             | WasmFeatures::GC
             | WasmFeatures::GC_TYPES
             | WasmFeatures::CUSTOM_PAGE_SIZES
-            | WasmFeatures::EXTENDED_CONST;
+            | WasmFeatures::EXTENDED_CONST
+            | WasmFeatures::EXCEPTIONS;
 
         // All other features that wasmparser supports, which is presumably a
         // superset of the features that wasm-smith supports, are listed here as

crates/fuzzing/src/oracles/diff_spec.rs

@@ -28,6 +28,7 @@ impl SpecInterpreter {
         config.custom_page_sizes_enabled = false;
         config.wide_arithmetic_enabled = false;
         config.extended_const_enabled = false;
+        config.exceptions_enabled = false;
 
         Self
     }