Fix fuzzers requesting 4gb memories (#3029)

Wasmtime was updated to reject creation of memories exactly 4gb in size
in #3013, but the fuzzers still had the assumption that any request to
create a host object for a particular wasm type would succeed.
Unfortunately now, though, a request to create a 4gb memory fails. This
is an expected failure, though, so the fix here was to catch the error
and allow it.

crates/fuzzing/src/oracles.rs

@@ -137,7 +137,24 @@ pub fn instantiate_with_config(
         Err(_) if !known_valid => return,
         Err(e) => panic!("failed to compile module: {:?}", e),
     };
-    let linker = dummy_linker(&mut store, &module);
+    let linker = match dummy_linker(&mut store, &module) {
+        Ok(linker) => linker,
+        Err(e) => {
+            eprintln!("Warning: failed to create host imports: {:?}", e);
+
+            // Currently the only error we want to allow here is ones where we
+            // ran out of resources creating imports. For example memory
+            // creation may not succeed if the host is running low on resources.
+            //
+            // Other errors, however, are bugs in creation of the host resource.
+            let string = e.to_string();
+            assert!(
+                string.contains("Insufficient resources")
+                    && string.contains("exceeds memory limits")
+            );
+            return;
+        }
+    };
 
     match linker.instantiate(&mut store, &module) {
         Ok(_) => {}
@@ -227,7 +244,13 @@ pub fn differential_execution(
         // in and with what values. Like the results of exported functions,
         // calls to imports should also yield the same values for each
         // configuration, and we should assert that.
-        let linker = dummy_linker(&mut store, &module);
+        let linker = match dummy_linker(&mut store, &module) {
+            Ok(linker) => linker,
+            Err(e) => {
+                eprintln!("Warning: failed to create host imports: {:?}", e);
+                continue;
+            }
+        };
 
         // Don't unwrap this: there can be instantiation-/link-time errors that
         // aren't caught during validation or compilation. For example, an imported
@@ -397,7 +420,10 @@ pub fn make_api_calls(api: crate::generators::api::ApiCalls) {
                 };
 
                 let store = store.as_mut().unwrap();
-                let linker = dummy_linker(store, module);
+                let linker = match dummy_linker(store, module) {
+                    Ok(linker) => linker,
+                    Err(_) => continue,
+                };
 
                 // Don't unwrap this: there can be instantiation-/link-time errors that
                 // aren't caught during validation or compilation. For example, an imported

crates/fuzzing/src/oracles/dummy.rs

@@ -1,48 +1,49 @@
 //! Dummy implementations of things that a Wasm module can import.
 
+use anyhow::Result;
 use std::fmt::Write;
 use wasmtime::*;
 
 /// Create a set of dummy functions/globals/etc for the given imports.
-pub fn dummy_linker<'module, T>(store: &mut Store<T>, module: &Module) -> Linker<T> {
+pub fn dummy_linker<'module, T>(store: &mut Store<T>, module: &Module) -> Result<Linker<T>> {
     let mut linker = Linker::new(store.engine());
     linker.allow_shadowing(true);
     for import in module.imports() {
         match import.name() {
             Some(name) => {
                 linker
-                    .define(import.module(), name, dummy_extern(store, import.ty()))
+                    .define(import.module(), name, dummy_extern(store, import.ty())?)
                     .unwrap();
             }
             None => match import.ty() {
                 ExternType::Instance(ty) => {
                     for ty in ty.exports() {
                         linker
-                            .define(import.module(), ty.name(), dummy_extern(store, ty.ty()))
+                            .define(import.module(), ty.name(), dummy_extern(store, ty.ty())?)
                             .unwrap();
                     }
                 }
                 other => {
                     linker
-                        .define_name(import.module(), dummy_extern(store, other))
+                        .define_name(import.module(), dummy_extern(store, other)?)
                         .unwrap();
                 }
             },
         }
     }
-    linker
+    Ok(linker)
 }
 
 /// Construct a dummy `Extern` from its type signature
-pub fn dummy_extern<T>(store: &mut Store<T>, ty: ExternType) -> Extern {
+pub fn dummy_extern<T>(store: &mut Store<T>, ty: ExternType) -> Result<Extern> {
-    match ty {
+    Ok(match ty {
         ExternType::Func(func_ty) => Extern::Func(dummy_func(store, func_ty)),
         ExternType::Global(global_ty) => Extern::Global(dummy_global(store, global_ty)),
         ExternType::Table(table_ty) => Extern::Table(dummy_table(store, table_ty)),
-        ExternType::Memory(mem_ty) => Extern::Memory(dummy_memory(store, mem_ty)),
+        ExternType::Memory(mem_ty) => Extern::Memory(dummy_memory(store, mem_ty)?),
         ExternType::Instance(instance_ty) => Extern::Instance(dummy_instance(store, instance_ty)),
         ExternType::Module(module_ty) => Extern::Module(dummy_module(store.engine(), module_ty)),
-    }
+    })
 }
 
 /// Construct a dummy function for the given function type
@@ -86,8 +87,8 @@ pub fn dummy_table<T>(store: &mut Store<T>, ty: TableType) -> Table {
 }
 
 /// Construct a dummy memory for the given memory type.
-pub fn dummy_memory<T>(store: &mut Store<T>, ty: MemoryType) -> Memory {
+pub fn dummy_memory<T>(store: &mut Store<T>, ty: MemoryType) -> Result<Memory> {
-    Memory::new(store, ty).unwrap()
+    Memory::new(store, ty)
 }
 
 /// Construct a dummy instance for the given instance type.
@@ -414,7 +415,7 @@ mod tests {
     #[test]
     fn dummy_memory_import() {
         let mut store = store();
-        let memory = dummy_memory(&mut store, MemoryType::new(Limits::at_least(1)));
+        let memory = dummy_memory(&mut store, MemoryType::new(Limits::at_least(1))).unwrap();
         assert_eq!(memory.size(&store), 1);
     }