wazevo: handle empty host module (#2125)

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

builder_test.go

@@ -308,7 +308,9 @@ func TestNewHostModuleBuilder_Compile(t *testing.T) {
 		tc := tt
 
 		t.Run(tc.name, func(t *testing.T) {
-			b := tc.input(NewRuntime(testCtx)).(*hostModuleBuilder)
+			cfg := NewRuntimeConfig()
+			cfg.(*runtimeConfig).EnableOptimizingCompiler()
+			b := tc.input(NewRuntimeWithConfig(testCtx, cfg)).(*hostModuleBuilder)
 			compiled, err := b.Compile(testCtx)
 			require.NoError(t, err)
 			m := compiled.(*compiledModule)

internal/engine/wazevo/engine.go

@@ -437,6 +437,11 @@ func (e *engine) compileHostModule(ctx context.Context, module *wasm.Module, lis
 		totalSize += len(body)
 	}
 
+	if totalSize == 0 {
+		// Empty module.
+		return cm, nil
+	}
+
 	// Allocate executable memory and then copy the generated machine code.
 	executable, err := platform.MmapCodeSegment(totalSize)
 	if err != nil {