From a199be5c18f8ce53e64acfe8fba89f1fc303b6f1 Mon Sep 17 00:00:00 2001
From: Pierrick Couderc <pierrick.couderc@nomadic-labs.com>
Date: Wed, 30 Nov 2022 14:43:09 +0100
Subject: [PATCH] WASM/PVM: improve error reporting when `kernel_run` is not
 defined

---
 src/lib_scoru_wasm/test/test_init.ml | 61 ++++++++++++++++++++++++++++
 src/lib_scoru_wasm/wasm_vm.ml        | 20 ++++++---
 2 files changed, 76 insertions(+), 5 deletions(-)

diff --git a/src/lib_scoru_wasm/test/test_init.ml b/src/lib_scoru_wasm/test/test_init.ml
index d8510512ac74..ea383cb00d64 100644
--- a/src/lib_scoru_wasm/test/test_init.ml
+++ b/src/lib_scoru_wasm/test/test_init.ml
@@ -197,6 +197,62 @@ let test_host_func_start_restriction () =
         "host functions must not access memory during initialisation"
       stuck)
 
+let test_bad_entrypoint_name () =
+  let open Lwt_result_syntax in
+  let module_ =
+    {|
+      (module
+        (memory 1)
+        (export "mem"(memory 0))
+        (func (export "bad_entrypoint")
+          (unreachable)
+        )
+      )|}
+  in
+
+  let*! bad_module_tree = initial_tree module_ in
+  let*! bad_module_tree = eval_until_input_requested bad_module_tree in
+  let*! bad_module_tree = set_empty_inbox_step 0l bad_module_tree in
+  let* stuck, _ = eval_until_stuck bad_module_tree in
+  assert (
+    check_error
+      ~expected_kind:`Invalid_state
+      ~expected_reason:
+        (Format.sprintf
+           "Invalid_module: no `%s` function exported"
+           Constants.wasm_entrypoint)
+      stuck) ;
+  return_unit
+
+(* `kernel_run` will be found, but this is not a function. *)
+let test_bad_export () =
+  let open Lwt_result_syntax in
+  let module_ =
+    {|
+      (module
+        (memory 1)
+        (export "kernel_run" (memory 0))
+        (func (export "bad_entrypoint")
+          (unreachable)
+        )
+      )|}
+  in
+
+  let*! bad_module_tree = initial_tree module_ in
+  let*! bad_module_tree = eval_until_input_requested bad_module_tree in
+  let*! bad_module_tree = set_empty_inbox_step 0l bad_module_tree in
+  let* stuck, _ = eval_until_stuck bad_module_tree in
+  Format.printf "%a\n%!" pp_state (Stuck stuck) ;
+  assert (
+    check_error
+      ~expected_kind:`Invalid_state
+      ~expected_reason:
+        (Format.sprintf
+           "Invalid_module: no `%s` function exported"
+           Constants.wasm_entrypoint)
+      stuck) ;
+  return_unit
+
 let tests =
   [
     tztest "init requires memory 0 export" `Quick test_memory0_export;
@@ -206,4 +262,9 @@ let tests =
       "host functions are restricted in start"
       `Quick
       test_host_func_start_restriction;
+    tztest "Check not found `kernel_run` error" `Quick test_bad_entrypoint_name;
+    tztest
+      "Check `kernel_run` not being a function error"
+      `Quick
+      test_bad_export;
   ]
diff --git a/src/lib_scoru_wasm/wasm_vm.ml b/src/lib_scoru_wasm/wasm_vm.ml
index 2972f7457e8e..641cd16d60a7 100644
--- a/src/lib_scoru_wasm/wasm_vm.ml
+++ b/src/lib_scoru_wasm/wasm_vm.ml
@@ -178,12 +178,20 @@ let unsafe_next_tick_state ({buffers; durable; tick_state; _} as pvm_state) =
         Wasm.Instance.ModuleMap.get Constants.wasm_main_module_name module_reg
       in
       let* extern =
-        Wasm.Instance.NameMap.get
-          Constants.wasm_entrypoint
-          module_inst.Wasm.Instance.exports
+        Lwt.catch
+          (fun () ->
+            let+ extern =
+              Wasm.Instance.NameMap.get
+                Constants.wasm_entrypoint
+                module_inst.Wasm.Instance.exports
+            in
+            Some extern)
+          (function
+            | Tezos_lazy_containers.Lazy_map.UnexpectedAccess -> return_none
+            | exn -> raise exn)
       in
       match extern with
-      | Wasm.Instance.ExternFunc main_func ->
+      | Some (Wasm.Instance.ExternFunc main_func) ->
           let admin_instr' = Wasm.Eval.Invoke main_func in
           let admin_instr = Wasm.Source.{it = admin_instr'; at = no_region} in
           (* Clear the values and the locals in the frame. *)
@@ -206,7 +214,9 @@ let unsafe_next_tick_state ({buffers; durable; tick_state; _} as pvm_state) =
             ~status:Failing
             (Stuck
                (Wasm_pvm_errors.invalid_state
-                  "Invalid_module: no `main` function exported")))
+                  (Format.sprintf
+                     "Invalid_module: no `%s` function exported"
+                     Constants.wasm_entrypoint))))
   | Init {self; ast_module; init_kont; module_reg} ->
       let* init_kont =
         Wasm.Eval.init_step
-- 
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