Improved offsets in module using pointer size rather than fixed numbers

src/webassembly/instance.rs

@@ -83,6 +83,10 @@ pub struct Instance {
     // 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,
+
     /// WebAssembly table data
     // pub tables: Arc<Vec<RwLock<Vec<usize>>>>,
     pub tables: Arc<Vec<Vec<usize>>>,
@@ -104,10 +108,6 @@ pub struct Instance {
     pub start_func: Option<FuncIndex>,
     // Region start memory location
     // code_base: *const (),
-
-    // Default memory bound
-    // TODO: Support for only one LinearMemory for now.
-    pub default_memory_bound: i32,
 }
 
 /// Contains pointers to data (heaps, globals, tables) needed

src/webassembly/module.rs

@@ -38,6 +38,35 @@ use cranelift_wasm::{
 use super::errors::ErrorKind;
 use super::memory::LinearMemory;
 
+/// Get the integer type used for representing pointers on this platform.
+fn native_pointer_type() -> ir::Type {
+    if cfg!(target_pointer_width = "64") {
+        ir::types::I64
+    } else {
+        ir::types::I32
+    }
+}
+
+/// Number of bytes in a native pointer.
+pub fn native_pointer_size() -> i32 {
+    if cfg!(target_pointer_width = "64") {
+        8
+    } else {
+        4
+    }
+}
+
+// /// Convert a TlsData offset into a `Offset32` for a global decl.
+// fn offset32(offset: usize) -> ir::immediates::Offset32 {
+//     assert!(offset <= i32::max_value() as usize);
+//     (offset as i32).into()
+// }
+
+// /// Convert a usize offset into a `Imm64` for an iadd_imm.
+// fn imm64(offset: usize) -> ir::immediates::Imm64 {
+//     (offset as i64).into()
+// }
+
 /// Compute a `ir::ExternalName` for a given wasm function index.
 fn get_func_name(func_index: FuncIndex) -> ir::ExternalName {
     ir::ExternalName::user(0, func_index.index() as u32)
@@ -337,8 +366,8 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
         // 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(0),
-            global_type: self.pointer_type(),
+            offset: Offset32::new(native_pointer_size() * 0),
+            global_type: native_pointer_type(),
         });
 
         // This will be 0 when the index is 0, not sure if the offset will work regardless
@@ -348,7 +377,7 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
         let base_gv = func.create_global_value(ir::GlobalValueData::Load {
             base: base,
             offset: Offset32::new(table_data_offset),
-            global_type: self.pointer_type(),
+            global_type: native_pointer_type(),
         });
 
         let bound_gv = func.create_global_value(ir::GlobalValueData::Load {
@@ -369,28 +398,28 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
     }
 
     fn make_heap(&mut self, func: &mut ir::Function, index: MemoryIndex) -> ir::Heap {
+        assert_eq!(index, 0, "Only one WebAssembly memory supported");
         // 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(8),
-            global_type: self.pointer_type(),
+            offset: Offset32::new(native_pointer_size() * 1), // 8
+            global_type: native_pointer_type(),
         });
 
-        let pointer_bytes = self.pointer_bytes();
-        let memories_offset = (index * pointer_bytes as usize) as i32;
+        let memories_offset = 0; // (index * pointer_bytes as usize) as i32;
 
         // We de-reference the vm_context.memories addr
         let heap_base = func.create_global_value(ir::GlobalValueData::Load {
             base: heap_base_addr,
             offset: Offset32::new(memories_offset),
-            global_type: self.pointer_type(),
+            global_type: native_pointer_type(),
         });
 
         let bound_gv = func.create_global_value(ir::GlobalValueData::Load {
             base: vmctx,
-            offset: Offset32::new(120),
+            offset: Offset32::new(native_pointer_size() * 3), // 24
             global_type: I32,
         });
 
@@ -454,15 +483,15 @@ impl<'environment> FuncEnvironmentTrait for FuncEnvironment<'environment> {
 
         let globals_base_addr = func.create_global_value(ir::GlobalValueData::Load {
             base: vmctx,
-            offset: Offset32::new(16),
-            global_type: self.pointer_type(),
+            offset: Offset32::new(native_pointer_size() * 2),
+            global_type: native_pointer_type(),
         });
 
-        let offset = (index * 8) as i64;
+        let offset = (index * native_pointer_size() as usize) as i64;
         let iadd = func.create_global_value(ir::GlobalValueData::IAddImm {
             base: globals_base_addr,
             offset: Imm64::new(offset),
-            global_type: self.pointer_type(),
+            global_type: native_pointer_type(),
         });
         GlobalVariable::Memory {
             gv: iadd,