1 use super::{truncate_i32_to_i16, truncate_i32_to_i8}; 2 use crate::{ 3 prelude::*, 4 runtime::vm::{GcHeap, GcStore, VMGcRef}, 5 store::AutoAssertNoGc, 6 vm::{FuncRefTableId, SendSyncPtr}, 7 AnyRef, ExternRef, Func, HeapType, RootedGcRefImpl, StorageType, Val, ValType, 8 }; 9 use core::fmt; 10 use wasmtime_environ::{GcStructLayout, VMGcKind}; 11 12 /// A `VMGcRef` that we know points to a `struct`. 13 /// 14 /// Create a `VMStructRef` via `VMGcRef::into_structref` and 15 /// `VMGcRef::as_structref`, or their untyped equivalents 16 /// `VMGcRef::into_structref_unchecked` and `VMGcRef::as_structref_unchecked`. 17 /// 18 /// Note: This is not a `TypedGcRef<_>` because each collector can have a 19 /// different concrete representation of `structref` that they allocate inside 20 /// their heaps. 21 #[derive(Debug, PartialEq, Eq, Hash)] 22 #[repr(transparent)] 23 pub struct VMStructRef(VMGcRef); 24 25 impl fmt::Pointer for VMStructRef { 26 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 27 fmt::Pointer::fmt(&self.0, f) 28 } 29 } 30 31 impl From<VMStructRef> for VMGcRef { 32 #[inline] 33 fn from(x: VMStructRef) -> Self { 34 x.0 35 } 36 } 37 38 impl VMGcRef { 39 /// Is this `VMGcRef` pointing to a `struct`? 40 pub fn is_structref(&self, gc_heap: &(impl GcHeap + ?Sized)) -> bool { 41 if self.is_i31() { 42 return false; 43 } 44 45 let header = gc_heap.header(&self); 46 header.kind().matches(VMGcKind::StructRef) 47 } 48 49 /// Create a new `VMStructRef` from the given `gc_ref`. 50 /// 51 /// If this is not a GC reference to an `structref`, `Err(self)` is 52 /// returned. 53 pub fn into_structref(self, gc_heap: &impl GcHeap) -> Result<VMStructRef, VMGcRef> { 54 if self.is_structref(gc_heap) { 55 Ok(self.into_structref_unchecked()) 56 } else { 57 Err(self) 58 } 59 } 60 61 /// Create a new `VMStructRef` from `self` without actually checking that 62 /// `self` is an `structref`. 63 /// 64 /// This method does not check that `self` is actually an `structref`, but 65 /// it should be. Failure to uphold this invariant is memory safe but will 66 /// result in general incorrectness down the line such as panics or wrong 67 /// results. 68 #[inline] 69 pub fn into_structref_unchecked(self) -> VMStructRef { 70 debug_assert!(!self.is_i31()); 71 VMStructRef(self) 72 } 73 74 /// Get this GC reference as an `structref` reference, if it actually is an 75 /// `structref` reference. 76 pub fn as_structref(&self, gc_heap: &(impl GcHeap + ?Sized)) -> Option<&VMStructRef> { 77 if self.is_structref(gc_heap) { 78 Some(self.as_structref_unchecked()) 79 } else { 80 None 81 } 82 } 83 84 /// Get this GC reference as an `structref` reference without checking if it 85 /// actually is an `structref` reference. 86 /// 87 /// Calling this method on a non-`structref` reference is memory safe, but 88 /// will lead to general incorrectness like panics and wrong results. 89 pub fn as_structref_unchecked(&self) -> &VMStructRef { 90 debug_assert!(!self.is_i31()); 91 let ptr = self as *const VMGcRef; 92 let ret = unsafe { &*ptr.cast() }; 93 assert!(matches!(ret, VMStructRef(VMGcRef { .. }))); 94 ret 95 } 96 } 97 98 impl VMStructRef { 99 /// Get the underlying `VMGcRef`. 100 pub fn as_gc_ref(&self) -> &VMGcRef { 101 &self.0 102 } 103 104 /// Clone this `VMStructRef`, running any GC barriers as necessary. 105 pub fn clone(&self, gc_store: &mut GcStore) -> Self { 106 Self(gc_store.clone_gc_ref(&self.0)) 107 } 108 109 /// Explicitly drop this `structref`, running GC drop barriers as necessary. 110 pub fn drop(self, gc_store: &mut GcStore) { 111 gc_store.drop_gc_ref(self.0); 112 } 113 114 /// Copy this `VMStructRef` without running the GC's clone barriers. 115 /// 116 /// Prefer calling `clone(&mut GcStore)` instead! This is mostly an internal 117 /// escape hatch for collector implementations. 118 /// 119 /// Failure to run GC barriers when they would otherwise be necessary can 120 /// lead to leaks, panics, and wrong results. It cannot lead to memory 121 /// unsafety, however. 122 pub fn unchecked_copy(&self) -> Self { 123 Self(self.0.unchecked_copy()) 124 } 125 126 /// Read a field of the given `StorageType` into a `Val`. 127 /// 128 /// `i8` and `i16` fields are zero-extended into `Val::I32(_)`s. 129 /// 130 /// Does not check that the field is actually of type `ty`. That is the 131 /// caller's responsibility. Failure to do so is memory safe, but will lead 132 /// to general incorrectness such as panics and wrong results. 133 /// 134 /// Panics on out-of-bounds accesses. 135 pub fn read_field( 136 &self, 137 store: &mut AutoAssertNoGc, 138 layout: &GcStructLayout, 139 ty: &StorageType, 140 field: usize, 141 ) -> Val { 142 let offset = layout.fields[field]; 143 let data = store.unwrap_gc_store_mut().gc_object_data(self.as_gc_ref()); 144 match ty { 145 StorageType::I8 => Val::I32(data.read_u8(offset).into()), 146 StorageType::I16 => Val::I32(data.read_u16(offset).into()), 147 StorageType::ValType(ValType::I32) => Val::I32(data.read_i32(offset)), 148 StorageType::ValType(ValType::I64) => Val::I64(data.read_i64(offset)), 149 StorageType::ValType(ValType::F32) => Val::F32(data.read_u32(offset)), 150 StorageType::ValType(ValType::F64) => Val::F64(data.read_u64(offset)), 151 StorageType::ValType(ValType::V128) => Val::V128(data.read_v128(offset)), 152 StorageType::ValType(ValType::Ref(r)) => match r.heap_type().top() { 153 HeapType::Extern => { 154 let raw = data.read_u32(offset); 155 Val::ExternRef(ExternRef::_from_raw(store, raw)) 156 } 157 HeapType::Any => { 158 let raw = data.read_u32(offset); 159 Val::AnyRef(AnyRef::_from_raw(store, raw)) 160 } 161 HeapType::Func => { 162 let func_ref_id = data.read_u32(offset); 163 let func_ref_id = FuncRefTableId::from_raw(func_ref_id); 164 let func_ref = store 165 .unwrap_gc_store() 166 .func_ref_table 167 .get_untyped(func_ref_id); 168 Val::FuncRef(unsafe { 169 func_ref.map(|p| Func::from_vm_func_ref(store, p.as_non_null())) 170 }) 171 } 172 otherwise => unreachable!("not a top type: {otherwise:?}"), 173 }, 174 } 175 } 176 177 /// Write the given value into this struct at the given offset. 178 /// 179 /// Returns an error if `val` is a GC reference that has since been 180 /// unrooted. 181 /// 182 /// Does not check that `val` matches `ty`, nor that the field is actually 183 /// of type `ty`. Checking those things is the caller's responsibility. 184 /// Failure to do so is memory safe, but will lead to general incorrectness 185 /// such as panics and wrong results. 186 /// 187 /// Panics on out-of-bounds accesses. 188 pub fn write_field( 189 &self, 190 store: &mut AutoAssertNoGc, 191 layout: &GcStructLayout, 192 ty: &StorageType, 193 field: usize, 194 val: Val, 195 ) -> Result<()> { 196 debug_assert!(val._matches_ty(&store, &ty.unpack())?); 197 198 let offset = layout.fields[field]; 199 let mut data = store.gc_store_mut()?.gc_object_data(self.as_gc_ref()); 200 match val { 201 Val::I32(i) if ty.is_i8() => data.write_i8(offset, truncate_i32_to_i8(i)), 202 Val::I32(i) if ty.is_i16() => data.write_i16(offset, truncate_i32_to_i16(i)), 203 Val::I32(i) => data.write_i32(offset, i), 204 Val::I64(i) => data.write_i64(offset, i), 205 Val::F32(f) => data.write_u32(offset, f), 206 Val::F64(f) => data.write_u64(offset, f), 207 Val::V128(v) => data.write_v128(offset, v), 208 209 // For GC-managed references, we need to take care to run the 210 // appropriate barriers, even when we are writing null references 211 // into the struct. 212 // 213 // POD-read the old value into a local copy, run the GC write 214 // barrier on that local copy, and then POD-write the updated 215 // value back into the struct. This avoids transmuting the inner 216 // data, which would probably be fine, but this approach is 217 // Obviously Correct and should get us by for now. If LLVM isn't 218 // able to elide some of these unnecessary copies, and this 219 // method is ever hot enough, we can always come back and clean 220 // it up in the future. 221 Val::ExternRef(e) => { 222 let raw = data.read_u32(offset); 223 let mut gc_ref = VMGcRef::from_raw_u32(raw); 224 let e = match e { 225 Some(e) => Some(e.try_gc_ref(store)?.unchecked_copy()), 226 None => None, 227 }; 228 store.gc_store_mut()?.write_gc_ref(&mut gc_ref, e.as_ref()); 229 let mut data = store.gc_store_mut()?.gc_object_data(self.as_gc_ref()); 230 data.write_u32(offset, gc_ref.map_or(0, |r| r.as_raw_u32())); 231 } 232 Val::AnyRef(a) => { 233 let raw = data.read_u32(offset); 234 let mut gc_ref = VMGcRef::from_raw_u32(raw); 235 let a = match a { 236 Some(a) => Some(a.try_gc_ref(store)?.unchecked_copy()), 237 None => None, 238 }; 239 store.gc_store_mut()?.write_gc_ref(&mut gc_ref, a.as_ref()); 240 let mut data = store.gc_store_mut()?.gc_object_data(self.as_gc_ref()); 241 data.write_u32(offset, gc_ref.map_or(0, |r| r.as_raw_u32())); 242 } 243 244 Val::FuncRef(f) => { 245 let f = f.map(|f| SendSyncPtr::new(f.vm_func_ref(store))); 246 let id = unsafe { store.gc_store_mut()?.func_ref_table.intern(f) }; 247 store 248 .gc_store_mut()? 249 .gc_object_data(self.as_gc_ref()) 250 .write_u32(offset, id.into_raw()); 251 } 252 } 253 Ok(()) 254 } 255 256 /// Initialize a field in this structref that is currently uninitialized. 257 /// 258 /// The difference between this method and `write_field` is that GC barriers 259 /// are handled differently. When overwriting an initialized field (aka 260 /// `write_field`) we need to call the full write GC write barrier, which 261 /// logically drops the old GC reference and clones the new GC 262 /// reference. When we are initializing a field for the first time, there is 263 /// no old GC reference that is being overwritten and which we need to drop, 264 /// so we only need to clone the new GC reference. 265 /// 266 /// Calling this method on a structref that has already had the associated 267 /// field initialized will result in GC bugs. These are memory safe but will 268 /// lead to generally incorrect behavior such as panics, leaks, and 269 /// incorrect results. 270 /// 271 /// Does not check that `val` matches `ty`, nor that the field is actually 272 /// of type `ty`. Checking those things is the caller's responsibility. 273 /// Failure to do so is memory safe, but will lead to general incorrectness 274 /// such as panics and wrong results. 275 /// 276 /// Returns an error if `val` is a GC reference that has since been 277 /// unrooted. 278 /// 279 /// Panics on out-of-bounds accesses. 280 pub fn initialize_field( 281 &self, 282 store: &mut AutoAssertNoGc, 283 layout: &GcStructLayout, 284 ty: &StorageType, 285 field: usize, 286 val: Val, 287 ) -> Result<()> { 288 debug_assert!(val._matches_ty(&store, &ty.unpack())?); 289 let offset = layout.fields[field]; 290 match val { 291 Val::I32(i) if ty.is_i8() => store 292 .gc_store_mut()? 293 .gc_object_data(self.as_gc_ref()) 294 .write_i8(offset, truncate_i32_to_i8(i)), 295 Val::I32(i) if ty.is_i16() => store 296 .gc_store_mut()? 297 .gc_object_data(self.as_gc_ref()) 298 .write_i16(offset, truncate_i32_to_i16(i)), 299 Val::I32(i) => store 300 .gc_store_mut()? 301 .gc_object_data(self.as_gc_ref()) 302 .write_i32(offset, i), 303 Val::I64(i) => store 304 .gc_store_mut()? 305 .gc_object_data(self.as_gc_ref()) 306 .write_i64(offset, i), 307 Val::F32(f) => store 308 .gc_store_mut()? 309 .gc_object_data(self.as_gc_ref()) 310 .write_u32(offset, f), 311 Val::F64(f) => store 312 .gc_store_mut()? 313 .gc_object_data(self.as_gc_ref()) 314 .write_u64(offset, f), 315 Val::V128(v) => store 316 .gc_store_mut()? 317 .gc_object_data(self.as_gc_ref()) 318 .write_v128(offset, v), 319 320 // NB: We don't need to do a write barrier when initializing a 321 // field, because there is nothing being overwritten. Therefore, we 322 // just the clone barrier. 323 Val::ExternRef(x) => { 324 let x = match x { 325 None => 0, 326 Some(x) => x.try_clone_gc_ref(store)?.as_raw_u32(), 327 }; 328 store 329 .gc_store_mut()? 330 .gc_object_data(self.as_gc_ref()) 331 .write_u32(offset, x); 332 } 333 Val::AnyRef(x) => { 334 let x = match x { 335 None => 0, 336 Some(x) => x.try_clone_gc_ref(store)?.as_raw_u32(), 337 }; 338 store 339 .gc_store_mut()? 340 .gc_object_data(self.as_gc_ref()) 341 .write_u32(offset, x); 342 } 343 344 Val::FuncRef(f) => { 345 let f = f.map(|f| SendSyncPtr::new(f.vm_func_ref(store))); 346 let id = unsafe { store.gc_store_mut()?.func_ref_table.intern(f) }; 347 store 348 .gc_store_mut()? 349 .gc_object_data(self.as_gc_ref()) 350 .write_u32(offset, id.into_raw()); 351 } 352 } 353 Ok(()) 354 } 355 } 356