1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
use super::{AllocId, InterpResult};

use rustc_macros::HashStable;
use rustc_target::abi::{HasDataLayout, Size};

use std::convert::TryFrom;
use std::fmt;

////////////////////////////////////////////////////////////////////////////////
// Pointer arithmetic
////////////////////////////////////////////////////////////////////////////////

pub trait PointerArithmetic: HasDataLayout {
    // These are not supposed to be overridden.

    #[inline(always)]
    fn pointer_size(&self) -> Size {
        self.data_layout().pointer_size
    }

    #[inline]
    fn machine_usize_max(&self) -> u64 {
        let max_usize_plus_1 = 1u128 << self.pointer_size().bits();
        u64::try_from(max_usize_plus_1 - 1).unwrap()
    }

    #[inline]
    fn machine_isize_min(&self) -> i64 {
        let max_isize_plus_1 = 1i128 << (self.pointer_size().bits() - 1);
        i64::try_from(-max_isize_plus_1).unwrap()
    }

    #[inline]
    fn machine_isize_max(&self) -> i64 {
        let max_isize_plus_1 = 1u128 << (self.pointer_size().bits() - 1);
        i64::try_from(max_isize_plus_1 - 1).unwrap()
    }

    #[inline]
    fn machine_usize_to_isize(&self, val: u64) -> i64 {
        let val = val as i64;
        // Now clamp into the machine_isize range.
        if val > self.machine_isize_max() {
            // This can only happen the the ptr size is < 64, so we know max_usize_plus_1 fits into
            // i64.
            let max_usize_plus_1 = 1u128 << self.pointer_size().bits();
            val - i64::try_from(max_usize_plus_1).unwrap()
        } else {
            val
        }
    }

    /// Helper function: truncate given value-"overflowed flag" pair to pointer size and
    /// update "overflowed flag" if there was an overflow.
    /// This should be called by all the other methods before returning!
    #[inline]
    fn truncate_to_ptr(&self, (val, over): (u64, bool)) -> (u64, bool) {
        let val = u128::from(val);
        let max_ptr_plus_1 = 1u128 << self.pointer_size().bits();
        (u64::try_from(val % max_ptr_plus_1).unwrap(), over || val >= max_ptr_plus_1)
    }

    #[inline]
    fn overflowing_offset(&self, val: u64, i: u64) -> (u64, bool) {
        // We do not need to check if i fits in a machine usize. If it doesn't,
        // either the wrapping_add will wrap or res will not fit in a pointer.
        let res = val.overflowing_add(i);
        self.truncate_to_ptr(res)
    }

    #[inline]
    fn overflowing_signed_offset(&self, val: u64, i: i64) -> (u64, bool) {
        // We need to make sure that i fits in a machine isize.
        let n = i.unsigned_abs();
        if i >= 0 {
            let (val, over) = self.overflowing_offset(val, n);
            (val, over || i > self.machine_isize_max())
        } else {
            let res = val.overflowing_sub(n);
            let (val, over) = self.truncate_to_ptr(res);
            (val, over || i < self.machine_isize_min())
        }
    }

    #[inline]
    fn offset<'tcx>(&self, val: u64, i: u64) -> InterpResult<'tcx, u64> {
        let (res, over) = self.overflowing_offset(val, i);
        if over { throw_ub!(PointerArithOverflow) } else { Ok(res) }
    }

    #[inline]
    fn signed_offset<'tcx>(&self, val: u64, i: i64) -> InterpResult<'tcx, u64> {
        let (res, over) = self.overflowing_signed_offset(val, i);
        if over { throw_ub!(PointerArithOverflow) } else { Ok(res) }
    }
}

impl<T: HasDataLayout> PointerArithmetic for T {}

/// This trait abstracts over the kind of provenance that is associated with a `Pointer`. It is
/// mostly opaque; the `Machine` trait extends it with some more operations that also have access to
/// some global state.
/// We don't actually care about this `Debug` bound (we use `Provenance::fmt` to format the entire
/// pointer), but `derive` adds some unecessary bounds.
pub trait Provenance: Copy + fmt::Debug {
    /// Says whether the `offset` field of `Pointer`s with this provenance is the actual physical address.
    /// If `true, ptr-to-int casts work by simply discarding the provenance.
    /// If `false`, ptr-to-int casts are not supported. The offset *must* be relative in that case.
    const OFFSET_IS_ADDR: bool;

    /// Determines how a pointer should be printed.
    fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result
    where
        Self: Sized;

    /// Provenance must always be able to identify the allocation this ptr points to.
    /// (Identifying the offset in that allocation, however, is harder -- use `Memory::ptr_get_alloc` for that.)
    fn get_alloc_id(self) -> AllocId;
}

impl Provenance for AllocId {
    // With the `AllocId` as provenance, the `offset` is interpreted *relative to the allocation*,
    // so ptr-to-int casts are not possible (since we do not know the global physical offset).
    const OFFSET_IS_ADDR: bool = false;

    fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Forward `alternate` flag to `alloc_id` printing.
        if f.alternate() {
            write!(f, "{:#?}", ptr.provenance)?;
        } else {
            write!(f, "{:?}", ptr.provenance)?;
        }
        // Print offset only if it is non-zero.
        if ptr.offset.bytes() > 0 {
            write!(f, "+0x{:x}", ptr.offset.bytes())?;
        }
        Ok(())
    }

    fn get_alloc_id(self) -> AllocId {
        self
    }
}

/// Represents a pointer in the Miri engine.
///
/// Pointers are "tagged" with provenance information; typically the `AllocId` they belong to.
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, TyEncodable, TyDecodable, Hash)]
#[derive(HashStable)]
pub struct Pointer<Tag = AllocId> {
    pub(super) offset: Size, // kept private to avoid accidental misinterpretation (meaning depends on `Tag` type)
    pub provenance: Tag,
}

static_assert_size!(Pointer, 16);

// We want the `Debug` output to be readable as it is used by `derive(Debug)` for
// all the Miri types.
impl<Tag: Provenance> fmt::Debug for Pointer<Tag> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        Provenance::fmt(self, f)
    }
}

impl<Tag: Provenance> fmt::Debug for Pointer<Option<Tag>> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.provenance {
            Some(tag) => Provenance::fmt(&Pointer::new(tag, self.offset), f),
            None => write!(f, "0x{:x}", self.offset.bytes()),
        }
    }
}

/// Produces a `Pointer` that points to the beginning of the `Allocation`.
impl From<AllocId> for Pointer {
    #[inline(always)]
    fn from(alloc_id: AllocId) -> Self {
        Pointer::new(alloc_id, Size::ZERO)
    }
}

impl<Tag> From<Pointer<Tag>> for Pointer<Option<Tag>> {
    #[inline(always)]
    fn from(ptr: Pointer<Tag>) -> Self {
        let (tag, offset) = ptr.into_parts();
        Pointer::new(Some(tag), offset)
    }
}

impl<Tag> Pointer<Option<Tag>> {
    pub fn into_pointer_or_addr(self) -> Result<Pointer<Tag>, Size> {
        match self.provenance {
            Some(tag) => Ok(Pointer::new(tag, self.offset)),
            None => Err(self.offset),
        }
    }
}

impl<Tag> Pointer<Option<Tag>> {
    #[inline(always)]
    pub fn null() -> Self {
        Pointer { provenance: None, offset: Size::ZERO }
    }
}

impl<'tcx, Tag> Pointer<Tag> {
    #[inline(always)]
    pub fn new(provenance: Tag, offset: Size) -> Self {
        Pointer { provenance, offset }
    }

    /// Obtain the constituents of this pointer. Not that the meaning of the offset depends on the type `Tag`!
    /// This function must only be used in the implementation of `Machine::ptr_get_alloc`,
    /// and when a `Pointer` is taken apart to be stored efficiently in an `Allocation`.
    #[inline(always)]
    pub fn into_parts(self) -> (Tag, Size) {
        (self.provenance, self.offset)
    }

    pub fn map_provenance(self, f: impl FnOnce(Tag) -> Tag) -> Self {
        Pointer { provenance: f(self.provenance), ..self }
    }

    #[inline]
    pub fn offset(self, i: Size, cx: &impl HasDataLayout) -> InterpResult<'tcx, Self> {
        Ok(Pointer {
            offset: Size::from_bytes(cx.data_layout().offset(self.offset.bytes(), i.bytes())?),
            ..self
        })
    }

    #[inline]
    pub fn overflowing_offset(self, i: Size, cx: &impl HasDataLayout) -> (Self, bool) {
        let (res, over) = cx.data_layout().overflowing_offset(self.offset.bytes(), i.bytes());
        let ptr = Pointer { offset: Size::from_bytes(res), ..self };
        (ptr, over)
    }

    #[inline(always)]
    pub fn wrapping_offset(self, i: Size, cx: &impl HasDataLayout) -> Self {
        self.overflowing_offset(i, cx).0
    }

    #[inline]
    pub fn signed_offset(self, i: i64, cx: &impl HasDataLayout) -> InterpResult<'tcx, Self> {
        Ok(Pointer {
            offset: Size::from_bytes(cx.data_layout().signed_offset(self.offset.bytes(), i)?),
            ..self
        })
    }

    #[inline]
    pub fn overflowing_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> (Self, bool) {
        let (res, over) = cx.data_layout().overflowing_signed_offset(self.offset.bytes(), i);
        let ptr = Pointer { offset: Size::from_bytes(res), ..self };
        (ptr, over)
    }

    #[inline(always)]
    pub fn wrapping_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> Self {
        self.overflowing_signed_offset(i, cx).0
    }
}