Actually check state root.

Also refactor wasm exports to be stricter on invalid mem references.

substrate/wasm-runtime/std/src/lib.rs

@@ -42,6 +42,7 @@ extern "C" {
 	fn ext_set_storage(key_data: *const u8, key_len: u32, value_data: *const u8, value_len: u32);
 	fn ext_get_allocated_storage(key_data: *const u8, key_len: u32, written_out: *mut u32) -> *mut u8;
 	fn ext_get_storage_into(key_data: *const u8, key_len: u32, value_data: *mut u8, value_len: u32, value_offset: u32) -> u32;
+	fn ext_storage_root(result: *mut u8);
 	fn ext_chain_id() -> u64;
 	fn ext_blake2_256(data: *const u8, len: u32, out: *mut u8);
 	fn ext_twox_128(data: *const u8, len: u32, out: *mut u8);
@@ -72,6 +73,15 @@ pub fn read_storage(key: &[u8], value_out: &mut [u8], value_offset: usize) -> us
 	}
 }
 
+/// The current storage's root.
+pub fn storage_root() -> [u8; 32] {
+	let mut result: [u8; 32] = Default::default();
+	unsafe {
+		ext_storage_root(result.as_mut_ptr());
+	}
+	result
+}
+
 /// The current relay chain identifier.
 pub fn chain_id() -> u64 {
 	unsafe {
@@ -82,7 +92,6 @@ pub fn chain_id() -> u64 {
 /// Conduct a 256-bit Blake2 hash.
 pub fn blake2_256(data: &[u8]) -> [u8; 32] {
 	let mut result: [u8; 32] = Default::default();
-	// guaranteed to write into result.
 	unsafe {
 		ext_blake2_256(data.as_ptr(), data.len() as u32, result.as_mut_ptr());
 	}
@@ -92,7 +101,6 @@ pub fn blake2_256(data: &[u8]) -> [u8; 32] {
 /// Conduct four XX hashes to give a 256-bit result.
 pub fn twox_256(data: &[u8]) -> [u8; 32] {
 	let mut result: [u8; 32] = Default::default();
-	// guaranteed to write into result.
 	unsafe {
 		ext_twox_256(data.as_ptr(), data.len() as u32, result.as_mut_ptr());
 	}
@@ -102,7 +110,6 @@ pub fn twox_256(data: &[u8]) -> [u8; 32] {
 /// Conduct two XX hashes to give a 128-bit result.
 pub fn twox_128(data: &[u8]) -> [u8; 16] {
 	let mut result: [u8; 16] = Default::default();
-	// guaranteed to write into result.
 	unsafe {
 		ext_twox_128(data.as_ptr(), data.len() as u32, result.as_mut_ptr());
 	}