Merge pull request #103 from WebAssembly/runaway-recursion

Handle interpreter stack overflow, and test runaway recursion.

ml-proto/TestingTodo.md

@@ -7,7 +7,7 @@ welcome.
 Misc semantics:
  - test that linear memory is little-endian for all integers and floats
  - test that unaligned and misaligned accesses work, even if slow
- - test that runaway recursion traps
+ - ~~test that runaway recursion traps~~
  - test that too-big linear memory resize fails appropriately
  - test that too-big linear memory initial allocation fails
  - test that function addresses are monotonic indices, and not actual addresses.

ml-proto/spec/eval.ml

@@ -105,6 +105,9 @@ let mem_size v at =
   let i64 = Int64.of_int32 i32 in
   Int64.shift_right_logical (Int64.shift_left i64 32) 32
 
+let callstack_exhaustion at =
+  error at ("runtime: callstack exhausted")
+
 
 (* Evaluation *)
 
@@ -296,9 +299,11 @@ let init m imports host =
   {funcs; imports; exports; tables; memory = memory'; host}
 
 let invoke m name vs =
-  let f = export m (name @@ no_region) in
-  assert (List.length vs = List.length f.it.params);
-  eval_func m f vs
+  try
+    let f = export m (name @@ no_region) in
+    assert (List.length vs = List.length f.it.params);
+    eval_func m f vs
+  with Stack_overflow -> callstack_exhaustion no_region
 
 (* This function is not part of the spec. *)
 let host_eval e =

ml-proto/test/fac.wast

@@ -71,3 +71,4 @@
 (assert_return (invoke "fac-iter" (i64.const 25)) (i64.const 7034535277573963776))
 (assert_return (invoke "fac-rec-named" (i64.const 25)) (i64.const 7034535277573963776))
 (assert_return (invoke "fac-iter-named" (i64.const 25)) (i64.const 7034535277573963776))
+(assert_trap (invoke "fac-rec" (i64.const 1073741824)) "runtime: callstack exhausted")

ml-proto/test/runaway-recursion.wast

@@ -0,0 +1,17 @@
+(module
+  ;; Implementations are required to have every call consume some abstract
+  ;; resource towards exhausting some abstract finite limit, such that
+  ;; infinitely recursive testcases reliably trap in finite time. This is
+  ;; because otherwise applications could come to depend on it on those
+  ;; implementations and be incompatible with implementations that don't do
+  ;; it (or don't do it under the same circumstances).
+  (func (call 0))
+  (export "runaway" 0)
+
+  (func $a (call $b))
+  (func $b (call $a))
+  (export "mutual_runaway" $a)
+)
+
+(assert_trap (invoke "runaway") "runtime: callstack exhausted")
+(assert_trap (invoke "mutual_runaway") "runtime: callstack exhausted")