use u8 repr as result and convert to err

Cargo.toml

@@ -136,6 +136,7 @@ jsonrpsee = { version = "^0.16" }
 lazy_static = "1.4.0"
 libc = { version = "0.2", default-features = false }
 log = { version = "0.4.17", default-features = false }
+num_enum = { version = "0.6.1", default-features = false }
 once_cell = "1.17.1"
 parity-scale-codec = { version = "3.6.4", default-features = false }
 parity-wasm = "0.45.0"

common/lazy-pages/src/lib.rs

@@ -184,7 +184,9 @@ pub fn pre_process_memory_accesses(
         gas_left.allowance,
     );
     *gas_left = gas_left_new;
-    if let Err(err) = res {
+
+    // if result can be converted to `ProcessAccessError` then it's an error
+    if let Ok(err) = ProcessAccessError::try_from(res) {
         return Err(err);
     }
     Ok(())

core-backend/common/Cargo.toml

@@ -15,6 +15,7 @@ blake2-rfc.workspace = true
 derive_more.workspace = true
 gsys.workspace = true
 log.workspace = true
+num_enum.workspace = true
 parity-scale-codec.workspace = true
 scale-info = { workspace = true, features = ["derive"] }
 

core-backend/common/src/memory.rs

@@ -37,15 +37,16 @@ use gear_core::{
     memory::{Memory, MemoryError, MemoryInterval},
 };
 use gear_core_errors::MemoryError as FallibleMemoryError;
-use scale_info::scale::{self, Decode, DecodeAll, Encode, MaxEncodedLen};
+use num_enum::{IntoPrimitive, TryFromPrimitive};
+use scale_info::scale::{Decode, DecodeAll, Encode, MaxEncodedLen};
 
 /// Memory access error during sys-call that lazy-pages have caught.
-#[derive(Debug, Clone, Encode, Decode)]
-#[codec(crate = scale)]
+#[derive(Debug, Clone, Encode, Decode, IntoPrimitive, TryFromPrimitive)]
+#[repr(u8)]
 pub enum ProcessAccessError {
-    OutOfBounds,
-    GasLimitExceeded,
-    GasAllowanceExceeded,
+    OutOfBounds = 1,
+    GasLimitExceeded = 2,
+    GasAllowanceExceeded = 3,
 }
 
 #[derive(Debug, Clone, derive_more::From)]

runtime-interface/src/lib.rs

@@ -101,7 +101,7 @@ pub trait GearRI {
         writes: &[u8],
         gas_left: u64,
         gas_allowance: u64,
-    ) -> (GasLeft, Result<(), ProcessAccessError>) {
+    ) -> (GasLeft, u8) {
         let reads_len = reads.len();
         let writes_len = writes.len();
         assert!(reads_len % 8 == 0);
@@ -114,11 +114,14 @@ pub trait GearRI {
             gas: gas_left,
             allowance: gas_allowance,
         };
-        let res = lazy_pages::pre_process_memory_accesses(
+        let res = match lazy_pages::pre_process_memory_accesses(
             &reads_intervals,
             &writes_intervals,
             &mut gas_left,
-        );
+        ) {
+            Ok(_) => 0,
+            Err(err) => err.into(),
+        };
         (gas_left, res)
     }