From 5d89d4ed857a3a0ff34cbcd6b72ce764c300c159 Mon Sep 17 00:00:00 2001
From: David Wendt <dcrkid@yahoo.com>
Date: Tue, 7 Jul 2020 21:28:24 -0400
Subject: [PATCH] Allow methods to not hold a body.

Interface methods are specifically not allowed to be called: as a result, they don't get a method body. Existing code assumed a 1:1 relationship between methods and bodies, which causes spurious errors.
---
 core/src/avm2/activation.rs | 21 +++++++++++++++------
 core/src/avm2/function.rs   |  2 +-
 core/src/avm2/method.rs     | 29 +++++++++++++++++++----------
 core/src/avm2/object.rs     |  2 +-
 4 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/core/src/avm2/activation.rs b/core/src/avm2/activation.rs
index e936a06c1..ac2073707 100644
--- a/core/src/avm2/activation.rs
+++ b/core/src/avm2/activation.rs
@@ -139,7 +139,10 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
     ) -> Result<Self, Error> {
         let method = script.read().init().into_bytecode()?;
         let scope = Some(Scope::push_scope(None, global, context.gc_context));
-        let num_locals = method.body().num_locals;
+        let body: Result<_, Error> = method
+            .body()
+            .ok_or_else(|| "Cannot execute non-native method (for script) without body".into());
+        let num_locals = body?.num_locals;
         let local_registers =
             GcCell::allocate(context.gc_context, RegisterSet::new(num_locals + 1));
 
@@ -171,8 +174,11 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
         this: Option<Object<'gc>>,
         arguments: &[Value<'gc>],
         base_proto: Option<Object<'gc>>,
-    ) -> Self {
-        let num_locals = method.body().num_locals;
+    ) -> Result<Self, Error> {
+        let body: Result<_, Error> = method
+            .body()
+            .ok_or_else(|| "Cannot execute non-native method without body".into());
+        let num_locals = body?.num_locals;
         let num_declared_arguments = method.method().params.len() as u32;
         let local_registers = GcCell::allocate(
             context.gc_context,
@@ -191,7 +197,7 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
             }
         }
 
-        Self {
+        Ok(Self {
             avm2,
             this,
             arguments: None,
@@ -201,7 +207,7 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
             local_scope: ScriptObject::bare_object(context.gc_context),
             scope,
             base_proto,
-        }
+        })
     }
 
     /// Execute a script initializer.
@@ -380,7 +386,10 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
         method: Gc<'gc, BytecodeMethod<'gc>>,
         context: &mut UpdateContext<'_, 'gc, '_>,
     ) -> Result<Value<'gc>, Error> {
-        let mut read = Reader::new(Cursor::new(method.body().code.as_ref()));
+        let body: Result<_, Error> = method
+            .body()
+            .ok_or_else(|| "Cannot execute non-native method without body".into());
+        let mut read = Reader::new(Cursor::new(body?.code.as_ref()));
 
         loop {
             let result = self.do_next_opcode(method, context, &mut read);
diff --git a/core/src/avm2/function.rs b/core/src/avm2/function.rs
index 75e43efbc..62e8be5b5 100644
--- a/core/src/avm2/function.rs
+++ b/core/src/avm2/function.rs
@@ -107,7 +107,7 @@ impl<'gc> Executable<'gc> {
                     reciever,
                     arguments,
                     base_proto,
-                );
+                )?;
 
                 activation.run_actions(bm.method, context)
             }
diff --git a/core/src/avm2/method.rs b/core/src/avm2/method.rs
index 3d9e49d25..1ca6cbb5a 100644
--- a/core/src/avm2/method.rs
+++ b/core/src/avm2/method.rs
@@ -50,7 +50,7 @@ pub struct BytecodeMethod<'gc> {
     pub abc_method: u32,
 
     /// The ABC method body this function uses.
-    pub abc_method_body: u32,
+    pub abc_method_body: Option<u32>,
 }
 
 impl<'gc> BytecodeMethod<'gc> {
@@ -74,14 +74,22 @@ impl<'gc> BytecodeMethod<'gc> {
                             txunit,
                             abc: CollectWrapper(txunit.abc()),
                             abc_method: abc_method.0,
-                            abc_method_body: index as u32,
+                            abc_method_body: Some(index as u32),
                         },
                     ));
                 }
             }
         }
 
-        None
+        Some(Gc::allocate(
+            mc,
+            Self {
+                txunit,
+                abc: CollectWrapper(txunit.abc()),
+                abc_method: abc_method.0,
+                abc_method_body: None,
+            },
+        ))
     }
 
     /// Get the underlying ABC file.
@@ -101,13 +109,14 @@ impl<'gc> BytecodeMethod<'gc> {
     }
 
     /// Get a reference to the ABC method body entry this refers to.
-    pub fn body(&self) -> &AbcMethodBody {
-        &self
-            .abc
-            .0
-            .method_bodies
-            .get(self.abc_method_body as usize)
-            .unwrap()
+    ///
+    /// Some methods do not have bodies; this returns `None` in that case.
+    pub fn body(&self) -> Option<&AbcMethodBody> {
+        if let Some(abc_method_body) = self.abc_method_body {
+            self.abc.0.method_bodies.get(abc_method_body as usize)
+        } else {
+            None
+        }
     }
 }
 
diff --git a/core/src/avm2/object.rs b/core/src/avm2/object.rs
index 056da591d..4ecc5fd38 100644
--- a/core/src/avm2/object.rs
+++ b/core/src/avm2/object.rs
@@ -427,7 +427,7 @@ pub trait TObject<'gc>: 'gc + Collect + Debug + Into<Object<'gc>> + Clone + Copy
         avm_debug!(
             "Installing trait {:?} of kind {:?}",
             trait_name,
-            trait_entry.kind
+            trait_entry.kind()
         );
 
         match trait_entry.kind() {