Improved instance & module data pointers location

src/webassembly/instance.rs

@@ -78,7 +78,11 @@ fn get_function_addr(
 
 /// An Instance of a WebAssembly module
 #[derive(Debug)]
+#[repr(C)]
 pub struct Instance {
+    // C-like pointers to data (heaps, globals, tables)
+    pub data_pointers: DataPointers,
+
     /// WebAssembly table data
     // pub tables: Arc<Vec<RwLock<Vec<usize>>>>,
     pub tables: Arc<Vec<Vec<usize>>>,
@@ -101,9 +105,6 @@ pub struct Instance {
     // Region start memory location
     // code_base: *const (),
 
-    // C-like pointers to data (heaps, globals, tables)
-    pub data_pointers: DataPointers,
-
     // Default memory bound
     // TODO: Support for only one LinearMemory for now.
     pub default_memory_bound: i32,
@@ -112,6 +113,7 @@ pub struct Instance {
 /// Contains pointers to data (heaps, globals, tables) needed
 /// by Cranelift.
 #[derive(Debug)]
+#[repr(C)]
 pub struct DataPointers {
     // Pointer to tables
     pub tables: UncheckedSlice<BoundedSlice<usize>>,

src/webassembly/module.rs

@@ -332,12 +332,12 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
         let vmctx = func.create_global_value(ir::GlobalValueData::VMContext);
         let ptr_size = self.ptr_size();
 
-        // Given a vmctx, we want to retrieve vmctx.tables
+        // Given a instance, we want to retrieve instance.tables
-        // Create a table whose base address is stored at `vmctx+88`.
+        // Create a table whose base address is stored at `instance+0`.
-        // 88 is the offset of the vmctx.tables pointer respect to vmctx pointer
+        // 0 is the offset of the vmctx.tables pointer respect to vmctx pointer
         let base = func.create_global_value(ir::GlobalValueData::Load {
             base: vmctx,
-            offset: Offset32::new(88),
+            offset: Offset32::new(0),
             global_type: self.pointer_type(),
         });
 
@@ -369,12 +369,12 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
     }
 
     fn make_heap(&mut self, func: &mut ir::Function, index: MemoryIndex) -> ir::Heap {
-        // Create a static heap whose base address is stored at `vmctx+96`.
+        // Create a static heap whose base address is stored at `instance+8`.
         let vmctx = func.create_global_value(ir::GlobalValueData::VMContext);
 
         let heap_base_addr = func.create_global_value(ir::GlobalValueData::Load {
             base: vmctx,
-            offset: Offset32::new(96),
+            offset: Offset32::new(8),
             global_type: self.pointer_type(),
         });
 
@@ -454,7 +454,7 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
 
         let globals_base_addr = func.create_global_value(ir::GlobalValueData::Load {
             base: vmctx,
-            offset: Offset32::new(104),
+            offset: Offset32::new(16),
             global_type: self.pointer_type(),
         });
 
@@ -506,6 +506,7 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
             .special_param(ir::ArgumentPurpose::VMContext)
             .expect("Missing vmctx parameter");
 
+
         // The `callee` value is an index into a table of function pointers.
         // Apparently, that table is stored at absolute address 0 in this dummy environment.
         // TODO: Generate bounds checking code.
@@ -556,6 +557,9 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
             .special_param(ir::ArgumentPurpose::VMContext)
             .expect("Missing vmctx parameter");
 
+        // println!("POINTER BYTES {}", self.pointer_bytes());
+        // println!("POINTER SIZE {}", self.ptr_size());
+
         // Build a value list for the call instruction containing the call_args and the vmctx
         // parameter.
         let mut args = ir::ValueList::default();