Add a type parameter to VMOffsets for pointer size (#3020)

* Add a type parameter to `VMOffsets` for pointer size

This commit adds a type parameter to `VMOffsets` representing the
pointer size to improve computations in `wasmtime-runtime` which always
use a constant value of the host's pointer size. The type parameter is
`u8` for `wasmtime-cranelift`'s use case where cross-compilation may be
involved.

* fix lightbeam

crates/runtime/src/externref.rs

@@ -965,8 +965,20 @@ mod tests {
 
         let actual_offset = (ref_count_ptr as usize) - (extern_data_ptr as usize);
 
+        let offsets = wasmtime_environ::VMOffsets::from(wasmtime_environ::VMOffsetsFields {
+            ptr: 8,
+            num_signature_ids: 0,
+            num_imported_functions: 0,
+            num_imported_tables: 0,
+            num_imported_memories: 0,
+            num_imported_globals: 0,
+            num_defined_functions: 0,
+            num_defined_tables: 0,
+            num_defined_memories: 0,
+            num_defined_globals: 0,
+        });
         assert_eq!(
-            wasmtime_environ::VMOffsets::vm_extern_data_ref_count(),
+            offsets.vm_extern_data_ref_count(),
             actual_offset.try_into().unwrap(),
         );
     }
@@ -981,7 +993,7 @@ mod tests {
         let actual_offset = (next_ptr as usize) - (table_ptr as usize);
 
         let offsets = wasmtime_environ::VMOffsets::from(wasmtime_environ::VMOffsetsFields {
-            pointer_size: 8,
+            ptr: 8,
             num_signature_ids: 0,
             num_imported_functions: 0,
             num_imported_tables: 0,
@@ -1008,7 +1020,7 @@ mod tests {
         let actual_offset = (end_ptr as usize) - (table_ptr as usize);
 
         let offsets = wasmtime_environ::VMOffsets::from(wasmtime_environ::VMOffsetsFields {
-            pointer_size: 8,
+            ptr: 8,
             num_signature_ids: 0,
             num_imported_functions: 0,
             num_imported_tables: 0,

crates/runtime/src/instance.rs

@@ -27,7 +27,7 @@ use wasmtime_environ::wasm::{
     DataIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex, ElemIndex, EntityIndex,
     FuncIndex, GlobalIndex, MemoryIndex, TableElementType, TableIndex, WasmType,
 };
-use wasmtime_environ::{ir, Module, VMOffsets};
+use wasmtime_environ::{ir, HostPtr, Module, VMOffsets};
 
 mod allocator;
 
@@ -119,7 +119,7 @@ pub(crate) struct Instance {
     module: Arc<Module>,
 
     /// Offsets in the `vmctx` region, precomputed from the `module` above.
-    offsets: VMOffsets,
+    offsets: VMOffsets<HostPtr>,
 
     /// WebAssembly linear memory data.
     ///

crates/runtime/src/instance/allocator.rs

@@ -22,8 +22,8 @@ use wasmtime_environ::wasm::{
     DefinedFuncIndex, DefinedMemoryIndex, DefinedTableIndex, GlobalInit, SignatureIndex, WasmType,
 };
 use wasmtime_environ::{
-    ir, MemoryInitialization, MemoryInitializer, Module, ModuleType, TableInitializer, VMOffsets,
-    WASM_PAGE_SIZE,
+    ir, HostPtr, MemoryInitialization, MemoryInitializer, Module, ModuleType, TableInitializer,
+    VMOffsets, WASM_PAGE_SIZE,
 };
 
 mod pooling;
@@ -643,7 +643,7 @@ unsafe impl InstanceAllocator for OnDemandInstanceAllocator {
         let mut handle = {
             let instance = Instance {
                 module: req.module.clone(),
-                offsets: VMOffsets::new(std::mem::size_of::<*const u8>() as u8, &req.module),
+                offsets: VMOffsets::new(HostPtr, &req.module),
                 memories,
                 tables,
                 dropped_elements: EntitySet::with_capacity(req.module.passive_elements.len()),

crates/runtime/src/instance/allocator/pooling.rs

@@ -21,7 +21,7 @@ use std::mem;
 use std::sync::{Arc, Mutex};
 use wasmtime_environ::{
     entity::{EntitySet, PrimaryMap},
-    MemoryStyle, Module, Tunables, VMOffsets, VMOffsetsFields, WASM_PAGE_SIZE,
+    HostPtr, MemoryStyle, Module, Tunables, VMOffsets, VMOffsetsFields, WASM_PAGE_SIZE,
 };
 
 cfg_if::cfg_if! {
@@ -298,7 +298,7 @@ impl InstancePool {
 
         // Calculate the maximum size of an Instance structure given the limits
         let offsets = VMOffsets::from(VMOffsetsFields {
-            pointer_size: std::mem::size_of::<*const u8>() as u8,
+            ptr: HostPtr,
             num_signature_ids: module_limits.types,
             num_imported_functions: module_limits.imported_functions,
             num_imported_tables: module_limits.imported_tables,
@@ -358,10 +358,7 @@ impl InstancePool {
                 instance as _,
                 Instance {
                     module: self.empty_module.clone(),
-                    offsets: VMOffsets::new(
-                        std::mem::size_of::<*const u8>() as u8,
-                        &self.empty_module,
-                    ),
+                    offsets: VMOffsets::new(HostPtr, &self.empty_module),
                     memories: PrimaryMap::with_capacity(limits.memories as usize),
                     tables: PrimaryMap::with_capacity(limits.tables as usize),
                     dropped_elements: EntitySet::new(),
@@ -383,10 +380,7 @@ impl InstancePool {
         let instance = self.instance(index);
 
         instance.module = req.module.clone();
-        instance.offsets = VMOffsets::new(
-            std::mem::size_of::<*const u8>() as u8,
-            instance.module.as_ref(),
-        );
+        instance.offsets = VMOffsets::new(HostPtr, instance.module.as_ref());
         instance.host_state = std::mem::replace(&mut req.host_state, Box::new(()));
 
         let mut limiter = req.store.and_then(|s| (*s).limiter());
@@ -497,8 +491,7 @@ impl InstancePool {
         // should put everything back in a relatively pristine state for each
         // fresh allocation later on.
         instance.module = self.empty_module.clone();
-        instance.offsets =
-            VMOffsets::new(std::mem::size_of::<*const u8>() as u8, &self.empty_module);
+        instance.offsets = VMOffsets::new(HostPtr, &self.empty_module);
 
         self.free_list.lock().unwrap().push(index);
     }