1 use rustc::ty::{Ty, layout::{Size, LayoutOf}};
6 pub trait EvalContextExt<'tcx> {
10 ) -> InterpResult<'tcx>;
15 left: ImmTy<'tcx, Tag>,
16 right: ImmTy<'tcx, Tag>,
17 ) -> InterpResult<'tcx, (Scalar<Tag>, bool)>;
19 fn ptr_int_arithmetic(
25 ) -> InterpResult<'tcx, (Scalar<Tag>, bool)>;
31 ) -> InterpResult<'tcx, bool>;
33 fn pointer_offset_inbounds(
38 ) -> InterpResult<'tcx, Scalar<Tag>>;
41 impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
42 /// Test if the pointer is in-bounds of a live allocation.
44 fn pointer_inbounds(&self, ptr: Pointer<Tag>) -> InterpResult<'tcx> {
45 let (size, _align) = self.memory().get_size_and_align(ptr.alloc_id, AllocCheck::Live)?;
46 ptr.check_in_alloc(size, CheckInAllocMsg::InboundsTest)
52 left: ImmTy<'tcx, Tag>,
53 right: ImmTy<'tcx, Tag>,
54 ) -> InterpResult<'tcx, (Scalar<Tag>, bool)> {
55 use rustc::mir::BinOp::*;
57 trace!("ptr_op: {:?} {:?} {:?}", *left, bin_op, *right);
59 // If intptrcast is enabled, treat everything of integer *type* at integer *value*.
60 if self.memory().extra.rng.is_some() && left.layout.ty.is_integral() {
61 // This is actually an integer operation, so dispatch back to the core engine.
62 // TODO: Once intptrcast is the default, librustc_mir should never even call us
64 assert!(right.layout.ty.is_integral());
65 let l_bits = self.force_bits(left.imm.to_scalar()?, left.layout.size)?;
66 let r_bits = self.force_bits(right.imm.to_scalar()?, right.layout.size)?;
68 let left = ImmTy::from_scalar(Scalar::from_uint(l_bits, left.layout.size), left.layout);
69 let right = ImmTy::from_scalar(Scalar::from_uint(r_bits, left.layout.size), right.layout);
71 return self.binary_op(bin_op, left, right);
74 // Operations that support fat pointers
77 let eq = match (*left, *right) {
78 (Immediate::Scalar(left), Immediate::Scalar(right)) =>
79 self.ptr_eq(left.not_undef()?, right.not_undef()?)?,
80 (Immediate::ScalarPair(left1, left2), Immediate::ScalarPair(right1, right2)) =>
81 self.ptr_eq(left1.not_undef()?, right1.not_undef()?)? &&
82 self.ptr_eq(left2.not_undef()?, right2.not_undef()?)?,
83 _ => bug!("Type system should not allow comparing Scalar with ScalarPair"),
85 return Ok((Scalar::from_bool(if bin_op == Eq { eq } else { !eq }), false));
90 // Now we expect no more fat pointers.
91 let left_layout = left.layout;
92 let left = left.to_scalar()?;
93 let right_layout = right.layout;
94 let right = right.to_scalar()?;
95 debug_assert!(left.is_ptr() || right.is_ptr() || bin_op == Offset);
99 let pointee_ty = left_layout.ty
101 .expect("Offset called on non-ptr type")
103 let ptr = self.pointer_offset_inbounds(
106 right.to_isize(self)?,
110 // These need both to be pointer, and fail if they are not in the same location
111 Lt | Le | Gt | Ge | Sub if left.is_ptr() && right.is_ptr() => {
112 let left = left.to_ptr().expect("we checked is_ptr");
113 let right = right.to_ptr().expect("we checked is_ptr");
114 if left.alloc_id == right.alloc_id {
115 let res = match bin_op {
116 Lt => left.offset < right.offset,
117 Le => left.offset <= right.offset,
118 Gt => left.offset > right.offset,
119 Ge => left.offset >= right.offset,
121 // subtract the offsets
122 let left_offset = Scalar::from_uint(left.offset.bytes(), self.memory().pointer_size());
123 let right_offset = Scalar::from_uint(right.offset.bytes(), self.memory().pointer_size());
124 let layout = self.layout_of(self.tcx.types.usize)?;
125 return self.binary_op(
127 ImmTy::from_scalar(left_offset, layout),
128 ImmTy::from_scalar(right_offset, layout),
131 _ => bug!("We already established it has to be one of these operators."),
133 Ok((Scalar::from_bool(res), false))
135 // Both are pointers, but from different allocations.
136 err!(InvalidPointerMath)
139 Gt | Ge if left.is_ptr() && right.is_bits() => {
140 // "ptr >[=] integer" can be tested if the integer is small enough.
141 let left = left.to_ptr().expect("we checked is_ptr");
142 let right = right.to_bits(self.memory().pointer_size()).expect("we checked is_bits");
143 let (_alloc_size, alloc_align) = self.memory()
144 .get_size_and_align(left.alloc_id, AllocCheck::MaybeDead)
145 .expect("alloc info with MaybeDead cannot fail");
146 let min_ptr_val = u128::from(alloc_align.bytes()) + u128::from(left.offset.bytes());
147 let result = match bin_op {
148 Gt => min_ptr_val > right,
149 Ge => min_ptr_val >= right,
154 Ok((Scalar::from_bool(true), false))
156 // Sorry, can't tell.
157 err!(InvalidPointerMath)
160 // These work if the left operand is a pointer, and the right an integer
161 Add | BitAnd | Sub | Rem if left.is_ptr() && right.is_bits() => {
162 // Cast to i128 is fine as we checked the kind to be ptr-sized
163 self.ptr_int_arithmetic(
165 left.to_ptr().expect("we checked is_ptr"),
166 right.to_bits(self.memory().pointer_size()).expect("we checked is_bits"),
167 right_layout.abi.is_signed(),
170 // Commutative operators also work if the integer is on the left
171 Add | BitAnd if left.is_bits() && right.is_ptr() => {
172 // This is a commutative operation, just swap the operands
173 self.ptr_int_arithmetic(
175 right.to_ptr().expect("we checked is_ptr"),
176 left.to_bits(self.memory().pointer_size()).expect("we checked is_bits"),
177 left_layout.abi.is_signed(),
180 // Nothing else works
181 _ => err!(InvalidPointerMath),
189 ) -> InterpResult<'tcx, bool> {
190 let size = self.pointer_size();
191 if self.memory().extra.rng.is_some() {
192 // Just compare the integers.
193 // TODO: Do we really want to *always* do that, even when comparing two live in-bounds pointers?
194 let left = self.force_bits(left, size)?;
195 let right = self.force_bits(right, size)?;
196 return Ok(left == right);
198 Ok(match (left, right) {
199 (Scalar::Raw { .. }, Scalar::Raw { .. }) =>
200 left.to_bits(size)? == right.to_bits(size)?,
201 (Scalar::Ptr(left), Scalar::Ptr(right)) => {
202 // Comparison illegal if one of them is out-of-bounds, *unless* they
203 // are in the same allocation.
204 if left.alloc_id == right.alloc_id {
205 left.offset == right.offset
207 // Make sure both pointers are in-bounds.
208 // This accepts one-past-the end. Thus, there is still technically
209 // some non-determinism that we do not fully rule out when two
210 // allocations sit right next to each other. The C/C++ standards are
211 // somewhat fuzzy about this case, so pragmatically speaking I think
212 // for now this check is "good enough".
213 // FIXME: Once we support intptrcast, we could try to fix these holes.
214 // Dead allocations in miri cannot overlap with live allocations, but
215 // on read hardware this can easily happen. Thus for comparisons we require
216 // both pointers to be live.
217 if self.pointer_inbounds(left).is_ok() && self.pointer_inbounds(right).is_ok() {
218 // Two in-bounds (and hence live) pointers in different allocations are different.
221 return err!(InvalidPointerMath);
225 // Comparing ptr and integer.
226 (Scalar::Ptr(ptr), Scalar::Raw { data, size }) |
227 (Scalar::Raw { data, size }, Scalar::Ptr(ptr)) => {
228 assert_eq!(size as u64, self.pointer_size().bytes());
229 let bits = data as u64;
231 // Case I: Comparing real pointers with "small" integers.
232 // Really we should only do this for NULL, but pragmatically speaking on non-bare-metal systems,
233 // an allocation will never be at the very bottom of the address space.
234 // Such comparisons can arise when comparing empty slices, which sometimes are "fake"
235 // integer pointers (okay because the slice is empty) and sometimes point into a
237 // The most common source of such integer pointers is `NonNull::dangling()`, which
238 // equals the type's alignment. i128 might have an alignment of 16 bytes, but few types have
239 // alignment 32 or higher, hence the limit of 32.
240 // FIXME: Once we support intptrcast, we could try to fix these holes.
242 // Test if the pointer can be different from NULL or not.
243 // We assume that pointers that are not NULL are also not "small".
244 if !self.memory().ptr_may_be_null(ptr) {
249 let (alloc_size, alloc_align) = self.memory()
250 .get_size_and_align(ptr.alloc_id, AllocCheck::MaybeDead)
251 .expect("alloc info with MaybeDead cannot fail");
253 // Case II: Alignment gives it away
254 if ptr.offset.bytes() % alloc_align.bytes() == 0 {
255 // The offset maintains the allocation alignment, so we know `base+offset`
256 // is aligned by `alloc_align`.
257 // FIXME: We could be even more general, e.g., offset 2 into a 4-aligned
258 // allocation cannot equal 3.
259 if bits % alloc_align.bytes() != 0 {
260 // The integer is *not* aligned. So they cannot be equal.
264 // Case III: The integer is too big, and the allocation goes on a bit
265 // without wrapping around the address space.
267 // Compute the highest address at which this allocation could live.
268 // Substract one more, because it must be possible to add the size
269 // to the base address without overflowing; that is, the very last address
270 // of the address space is never dereferencable (but it can be in-bounds, i.e.,
271 // one-past-the-end).
273 ((1u128 << self.pointer_size().bits())
274 - u128::from(alloc_size.bytes())
277 if let Some(max_addr) = max_base_addr.checked_add(ptr.offset.bytes()) {
279 // The integer is too big, this cannot possibly be equal.
285 // None of the supported cases.
286 return err!(InvalidPointerMath);
291 fn ptr_int_arithmetic(
297 ) -> InterpResult<'tcx, (Scalar<Tag>, bool)> {
298 use rustc::mir::BinOp::*;
300 fn map_to_primval((res, over): (Pointer<Tag>, bool)) -> (Scalar<Tag>, bool) {
301 (Scalar::Ptr(res), over)
306 // The only way this can overflow is by underflowing, so signdeness of the right
307 // operands does not matter.
308 map_to_primval(left.overflowing_signed_offset(-(right as i128), self)),
310 map_to_primval(left.overflowing_signed_offset(right as i128, self)),
312 map_to_primval(left.overflowing_offset(Size::from_bytes(right as u64), self)),
314 BitAnd if !signed => {
315 let ptr_base_align = self.memory().get_size_and_align(left.alloc_id, AllocCheck::MaybeDead)
316 .expect("alloc info with MaybeDead cannot fail")
319 // FIXME: use `interpret::truncate`, once that takes a `Size` instead of a `Layout`.
320 let shift = 128 - self.memory().pointer_size().bits();
321 let value = !(ptr_base_align as u128 - 1);
322 // Truncate (shift left to drop out leftover values, shift right to fill with zeroes).
323 (value << shift) >> shift
325 let ptr_size = self.memory().pointer_size();
326 trace!("ptr BitAnd, align {}, operand {:#010x}, base_mask {:#010x}",
327 ptr_base_align, right, base_mask);
328 if right & base_mask == base_mask {
329 // Case 1: the base address bits are all preserved, i.e., right is all-1 there.
330 let offset = (left.offset.bytes() as u128 & right) as u64;
332 Scalar::Ptr(Pointer::new_with_tag(
334 Size::from_bytes(offset),
339 } else if right & base_mask == 0 {
340 // Case 2: the base address bits are all taken away, i.e., right is all-0 there.
341 let v = Scalar::from_uint((left.offset.bytes() as u128) & right, ptr_size);
344 return err!(ReadPointerAsBytes);
349 // Doing modulo a divisor of the alignment is allowed.
350 // (Intuition: modulo a divisor leaks less information.)
351 let ptr_base_align = self.memory().get_size_and_align(left.alloc_id, AllocCheck::MaybeDead)
352 .expect("alloc info with MaybeDead cannot fail")
354 let right = right as u64;
355 let ptr_size = self.memory().pointer_size();
357 // Modulo 1 is always 0.
358 (Scalar::from_uint(0u32, ptr_size), false)
359 } else if ptr_base_align % right == 0 {
360 // The base address would be cancelled out by the modulo operation, so we can
361 // just take the modulo of the offset.
363 Scalar::from_uint((left.offset.bytes() % right) as u128, ptr_size),
367 return err!(ReadPointerAsBytes);
373 "unimplemented binary op on pointer {:?}: {:?}, {:?} ({})",
377 if signed { "signed" } else { "unsigned" }
379 return err!(Unimplemented(msg));
384 /// Raises an error if the offset moves the pointer outside of its allocation.
385 /// We consider ZSTs their own huge allocation that doesn't overlap with anything (and nothing
386 /// moves in there because the size is 0). We also consider the NULL pointer its own separate
387 /// allocation, and all the remaining integers pointers their own allocation.
388 fn pointer_offset_inbounds(
391 pointee_ty: Ty<'tcx>,
393 ) -> InterpResult<'tcx, Scalar<Tag>> {
394 // FIXME: assuming here that type size is less than `i64::max_value()`.
395 let pointee_size = self.layout_of(pointee_ty)?.size.bytes() as i64;
397 .checked_mul(pointee_size)
398 .ok_or_else(|| InterpError::Overflow(mir::BinOp::Mul))?;
399 // Now let's see what kind of pointer this is.
400 let ptr = if offset == 0 {
402 Scalar::Ptr(ptr) => ptr,
403 Scalar::Raw { .. } => {
404 // Offset 0 on an integer. We accept that, pretending there is
405 // a little zero-sized allocation here.
410 // Offset > 0. We *require* a pointer.
413 // Both old and new pointer must be in-bounds of a *live* allocation.
414 // (Of the same allocation, but that part is trivial with our representation.)
415 self.pointer_inbounds(ptr)?;
416 let ptr = ptr.signed_offset(offset, self)?;
417 self.pointer_inbounds(ptr)?;