Test restoring zeroed data (#9011)

* Test restoring zeroed data

* Change to u64

substrate/client/executor/runtime-test/src/lib.rs

@@ -39,6 +39,14 @@ extern "C" {
 /// the initialized value at the start of a runtime call.
 static mut MUTABLE_STATIC: u64 = 32;
 
+#[cfg(not(feature = "std"))]
+/// This is similar to `MUTABLE_STATIC`. The tests need `MUTABLE_STATIC` for testing that
+/// non-null initialization data is properly restored during instance reusing.
+///
+/// `MUTABLE_STATIC_BSS` on the other hand focuses on the zeroed data. This is important since there
+/// may be differences in handling zeroed and non-zeroed data.
+static mut MUTABLE_STATIC_BSS: u64 = 0;
+
 sp_core::wasm_export_functions! {
 	fn test_calling_missing_external() {
 		unsafe { missing_external() }
@@ -309,6 +317,13 @@ sp_core::wasm_export_functions! {
 		}
 	}
 
+	fn returns_mutable_static_bss() -> u64 {
+		unsafe {
+			MUTABLE_STATIC_BSS += 1;
+			MUTABLE_STATIC_BSS
+		}
+	}
+
 	fn allocates_huge_stack_array(trap: bool) -> Vec<u8> {
 		// Allocate a stack frame that is approx. 75% of the stack (assuming it is 1MB).
 		// This will just decrease (stacks in wasm32-u-u grow downwards) the stack

substrate/client/executor/src/integration_tests/mod.rs

@@ -588,6 +588,25 @@ fn returns_mutable_static(wasm_method: WasmExecutionMethod) {
 	assert_eq!(33, u64::decode(&mut &res[..]).unwrap());
 }
 
+test_wasm_execution!(returns_mutable_static_bss);
+fn returns_mutable_static_bss(wasm_method: WasmExecutionMethod) {
+	let runtime = mk_test_runtime(wasm_method, 1024);
+
+	let instance = runtime.new_instance().unwrap();
+	let res = instance
+		.call_export("returns_mutable_static_bss", &[0])
+		.unwrap();
+	assert_eq!(1, u64::decode(&mut &res[..]).unwrap());
+
+	// We expect that every invocation will need to return the initial
+	// value plus one. If the value increases more than that then it is
+	// a sign that the wasm runtime preserves the memory content.
+	let res = instance
+		.call_export("returns_mutable_static_bss", &[0])
+		.unwrap();
+	assert_eq!(1, u64::decode(&mut &res[..]).unwrap());
+}
+
 // If we didn't restore the wasm instance properly, on a trap the stack pointer would not be
 // returned to its initial value and thus the stack space is going to be leaked.
 //