Alter invocation of functions to use 16-byte invocation arguments

wasmtime-environ/src/vmoffsets.rs

@@ -22,6 +22,11 @@ fn cast_to_u32(sz: usize) -> u32 {
     }
 }
 
+/// Align an offset used in this module to a specific byte-width by rounding up
+fn align(offset: u32, width: u32) -> u32 {
+    (offset + (width - 1)) / width * width
+}
+
 /// This class computes offsets to fields within `VMContext` and other
 /// related structs that JIT code accesses directly.
 pub struct VMOffsets {
@@ -208,9 +213,10 @@ impl VMOffsets {
 
 /// Offsets for `VMGlobalDefinition`.
 impl VMOffsets {
-    /// Return the size of `VMGlobalDefinition`.
+    /// Return the size of `VMGlobalDefinition`; this is the size of the largest value type (i.e. a
+    /// V128).
     pub fn size_of_vmglobal_definition(&self) -> u8 {
-        8
+        16
     }
 }
 
@@ -324,13 +330,15 @@ impl VMOffsets {
 
     /// The offset of the `globals` array.
     pub fn vmctx_globals_begin(&self) -> u32 {
-        self.vmctx_memories_begin()
+        let offset = self
+            .vmctx_memories_begin()
             .checked_add(
                 self.num_defined_memories
                     .checked_mul(u32::from(self.size_of_vmmemory_definition()))
                     .unwrap(),
             )
-            .unwrap()
+            .unwrap();
+        align(offset, 16)
     }
 
     /// The offset of the builtin functions array.
@@ -557,3 +565,19 @@ impl TargetSharedSignatureIndex {
         self.0
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::vmoffsets::align;
+
+    #[test]
+    fn alignment() {
+        fn is_aligned(x: u32) -> bool {
+            x % 16 == 0
+        }
+        assert!(is_aligned(align(0, 16)));
+        assert!(is_aligned(align(32, 16)));
+        assert!(is_aligned(align(33, 16)));
+        assert!(is_aligned(align(31, 16)));
+    }
+}

wasmtime-jit/src/action.rs

@@ -7,7 +7,7 @@ use core::{fmt, mem, ptr, slice};
 use cranelift_codegen::ir;
 use std::string::String;
 use std::vec::Vec;
-use wasmtime_runtime::{wasmtime_call_trampoline, Export, InstanceHandle};
+use wasmtime_runtime::{wasmtime_call_trampoline, Export, InstanceHandle, VMInvokeArgument};
 
 /// A runtime value.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -161,12 +161,12 @@ pub fn invoke(
         assert_eq!(value.value_type(), signature.params[index + 1].value_type);
     }
 
-    // TODO: Support values larger than u64. And pack the values into memory
+    // TODO: Support values larger than v128. And pack the values into memory
     // instead of just using fixed-sized slots.
     // Subtract one becase we don't pass the vmctx argument in `values_vec`.
-    let value_size = mem::size_of::<u64>();
-    let mut values_vec: Vec<u64> =
-        vec![0; max(signature.params.len() - 1, signature.returns.len())];
+    let value_size = mem::size_of::<VMInvokeArgument>();
+    let mut values_vec: Vec<VMInvokeArgument> =
+        vec![VMInvokeArgument::new(); max(signature.params.len() - 1, signature.returns.len())];
 
     // Store the argument values into `values_vec`.
     for (index, arg) in args.iter().enumerate() {

wasmtime-runtime/src/lib.rs

@@ -55,8 +55,8 @@ pub use crate::trap_registry::{get_mut_trap_registry, get_trap_registry, TrapReg
 pub use crate::traphandlers::{wasmtime_call, wasmtime_call_trampoline};
 pub use crate::vmcontext::{
     VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport, VMGlobalDefinition,
-    VMGlobalImport, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex, VMTableDefinition,
-    VMTableImport,
+    VMGlobalImport, VMInvokeArgument, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex,
+    VMTableDefinition, VMTableImport,
 };
 
 /// Version number of this crate.

wasmtime-runtime/src/vmcontext.rs

@@ -250,10 +250,10 @@ mod test_vmtable_definition {
 /// TODO: Pack the globals more densely, rather than using the same size
 /// for every type.
 #[derive(Debug, Copy, Clone)]
-#[repr(C, align(8))]
+#[repr(C, align(16))]
 pub struct VMGlobalDefinition {
-    storage: [u8; 8], // TODO this may need to be 16
-                      // If more elements are added here, remember to add offset_of tests below!
+    storage: [u8; 16],
+    // If more elements are added here, remember to add offset_of tests below!
 }
 
 #[cfg(test)]
@@ -268,6 +268,7 @@ mod test_vmglobal_definition {
         assert!(align_of::<VMGlobalDefinition>() >= align_of::<i64>());
         assert!(align_of::<VMGlobalDefinition>() >= align_of::<f32>());
         assert!(align_of::<VMGlobalDefinition>() >= align_of::<f64>());
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<[u8; 16]>());
     }
 
     #[test]
@@ -279,12 +280,19 @@ mod test_vmglobal_definition {
             usize::from(offsets.size_of_vmglobal_definition())
         );
     }
+
+    #[test]
+    fn check_vmglobal_begins_aligned() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(offsets.vmctx_globals_begin() % 16, 0);
+    }
 }
 
 impl VMGlobalDefinition {
     /// Construct a `VMGlobalDefinition`.
     pub fn new() -> Self {
-        Self { storage: [0; 8] }
+        Self { storage: [0; 16] }
     }
 
     /// Return a reference to the value as an i32.
@@ -533,6 +541,42 @@ impl VMBuiltinFunctionsArray {
     }
 }
 
+/// The storage for a WebAssembly invocation argument
+///
+/// TODO: These could be packed more densely, rather than using the same size for every type.
+#[derive(Debug, Copy, Clone)]
+#[repr(C, align(16))]
+pub struct VMInvokeArgument([u8; 16]);
+
+#[cfg(test)]
+mod test_vm_invoke_argument {
+    use super::VMInvokeArgument;
+    use core::mem::{align_of, size_of};
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vm_invoke_argument_alignment() {
+        assert_eq!(align_of::<VMInvokeArgument>(), 16);
+    }
+
+    #[test]
+    fn check_vmglobal_definition_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMInvokeArgument>(),
+            usize::from(offsets.size_of_vmglobal_definition())
+        );
+    }
+}
+
+impl VMInvokeArgument {
+    /// Create a new invocation argument filled with zeroes
+    pub fn new() -> Self {
+        VMInvokeArgument([0; 16])
+    }
+}
+
 /// The VM "context", which is pointed to by the `vmctx` arg in Cranelift.
 /// This has information about globals, memories, tables, and other runtime
 /// state associated with the current instance.