Teach stack limiter to handle start fn

src/stack_height/mod.rs

@@ -25,11 +25,12 @@
 //! Because stack height is increased prior the call few problems arises:
 //!
 //! - Stack height isn't increased upon an entry to the first function, i.e. exported function.
+//! - Start function is executed externally (similar to exported functions).
 //! - It is statically unknown what function will be invoked in an indirect call.
 //!
 //! The solution for this problems is to generate a intermediate functions, called 'thunks', which
 //! will increase before and decrease the stack height after the call to original function, and
-//! then make exported function and table entries to point to a corresponding thunks.
+//! then make exported function and table entries, start section to point to a corresponding thunks.
 //!
 //! # Stack cost
 //!

src/stack_height/thunk.rs

@@ -35,6 +35,8 @@ pub(crate) fn generate_thunks(
 			.elements_section()
 			.map(|es| es.entries())
 			.unwrap_or(&[]);
+		let start_func_idx = module
+			.start_section();
 
 		let exported_func_indicies = exports.iter().filter_map(|entry| match *entry.internal() {
 			Internal::Function(ref function_idx) => Some(*function_idx),
@@ -48,7 +50,7 @@ pub(crate) fn generate_thunks(
 		// Replacement map is at least export section size.
 		let mut replacement_map: Map<u32, Thunk> = Map::new();
 
-		for func_idx in exported_func_indicies.chain(table_func_indicies) {
+		for func_idx in exported_func_indicies.chain(table_func_indicies).chain(start_func_idx.into_iter()) {
 			let callee_stack_cost = ctx.stack_cost(func_idx).ok_or_else(|| {
 				Error(format!("function with idx {} isn't found", func_idx))
 			})?;
@@ -154,6 +156,9 @@ pub(crate) fn generate_thunks(
 					}
 				}
 			}
+			elements::Section::Start(ref mut start_idx) => {
+				fixup(start_idx)
+			}
 			_ => {}
 		}
 	}

tests/diff.rs

@@ -88,6 +88,7 @@ macro_rules! def_stack_height_test {
 }
 
 def_stack_height_test!(simple);
+def_stack_height_test!(start);
 def_stack_height_test!(table);
 def_stack_height_test!(global);
 def_stack_height_test!(imports);

tests/expectations/stack-height/start.wat

@@ -0,0 +1,44 @@
+(module
+  (type (;0;) (func (param i32 i32)))
+  (type (;1;) (func))
+  (import "env" "ext_return" (func (;0;) (type 0)))
+  (import "env" "memory" (memory (;0;) 1 1))
+  (func (;1;) (type 1)
+    (local i32))
+  (func (;2;) (type 1))
+  (func (;3;) (type 1)
+    get_global 0
+    i32.const 1
+    i32.add
+    set_global 0
+    get_global 0
+    i32.const 1024
+    i32.gt_u
+    if  ;; label = @1
+      unreachable
+    end
+    call 1
+    get_global 0
+    i32.const 1
+    i32.sub
+    set_global 0)
+  (func (;4;) (type 1)
+    get_global 0
+    i32.const 1
+    i32.add
+    set_global 0
+    get_global 0
+    i32.const 1024
+    i32.gt_u
+    if  ;; label = @1
+      unreachable
+    end
+    call 1
+    get_global 0
+    i32.const 1
+    i32.sub
+    set_global 0)
+  (global (;0;) (mut i32) (i32.const 0))
+  (export "exported_start" (func 4))
+  (export "call" (func 2))
+  (start 4))

tests/fixtures/stack-height/start.wat

@@ -0,0 +1,11 @@
+(module
+	(import "env" "ext_return" (func $ext_return (param i32 i32)))
+	(import "env" "memory" (memory 1 1))
+
+	(start $start)
+	(func $start (export "exported_start")
+		(local i32)
+	)
+	(func (export "call")
+	)
+)