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align_to and align_to_mut contract and harnesses #405

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106a110
align_to and align_to_mut contracts
AlexLB99 Jul 2, 2025
c2a64d8
Merge branch 'model-checking:main' into check_align_to
AlexLB99 Jul 2, 2025
9e62272
updated/added comments to slice/mod.rs
AlexLB99 Jul 2, 2025
31a8d89
Merge branch 'model-checking:main' into check_align_to
AlexLB99 Jul 22, 2025
fc2a863
moved align_to_mut_wrapper contract to align_to_mut
AlexLB99 Jul 22, 2025
68dd9ba
formatting
AlexLB99 Jul 22, 2025
ed67c16
Merge branch 'model-checking:main' into check_align_to
AlexLB99 Jul 23, 2025
7e8d09c
fixed mismerge
AlexLB99 Jul 23, 2025
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156 changes: 156 additions & 0 deletions library/core/src/slice/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,12 @@

#![stable(feature = "rust1", since = "1.0.0")]

use safety::{ensures, requires};

use crate::cmp::Ordering::{self, Equal, Greater, Less};
use crate::intrinsics::{exact_div, unchecked_sub};
#[cfg(kani)]
use crate::kani;
use crate::mem::{self, MaybeUninit, SizedTypeProperties};
use crate::num::NonZero;
use crate::ops::{OneSidedRange, OneSidedRangeBound, Range, RangeBounds, RangeInclusive};
Expand Down Expand Up @@ -4123,6 +4127,39 @@ impl<T> [T] {
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
#[must_use]
//Checks if the part that will be transmuted from type T to U is valid for type U
//reuses most function logic up to use of from_raw_parts,
//where the potentially unsafe transmute occurs
#[requires(
U::IS_ZST || T::IS_ZST || {
let ptr = self.as_ptr();
let offset = crate::ptr::align_offset(ptr, align_of::<U>());
offset > self.len() || {
let (_, rest) = self.split_at(offset);
let (us_len, _) = rest.align_to_offsets::<U>();
let middle = crate::ptr::slice_from_raw_parts(rest.as_ptr() as *const U, us_len);
crate::ub_checks::can_dereference(middle)
}
}
)]
//The following clause guarantees that middle is of maximum size within self
//If U or T are ZSTs, then middle has size zero, so we adapt the check in that case
#[ensures(|(prefix, _, suffix): &(&[T], &[U], &[T])|
((U::IS_ZST || T::IS_ZST) && prefix.len() == self.len()) || (
(prefix.len() * size_of::<T>() < align_of::<U>()) &&
(suffix.len() * size_of::<T>() < size_of::<U>())
)
)]
//Either align_to just returns self in the prefix, or the 3 returned slices
//should be sequential, contiguous, and have same total length as self
#[ensures(|(prefix, middle, suffix): &(&[T], &[U], &[T])|
prefix.as_ptr() == self.as_ptr() &&
(prefix.len() == self.len() || (
((prefix.as_ptr()).add(prefix.len()) as *const u8 == middle.as_ptr() as *const u8) &&
((middle.as_ptr()).add(middle.len()) as *const u8 == suffix.as_ptr() as *const u8) &&
((suffix.as_ptr()).add(suffix.len()) == (self.as_ptr()).add(self.len())) )
)
)]
pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
// Note that most of this function will be constant-evaluated,
if U::IS_ZST || T::IS_ZST {
Expand Down Expand Up @@ -4188,6 +4225,39 @@ impl<T> [T] {
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
#[must_use]
//Checks if the part that will be transmuted from type T to U is valid for type U
//reuses most function logic up to use of from_raw_parts,
//where the potentially unsafe transmute occurs
#[requires(
U::IS_ZST || T::IS_ZST || {
let ptr = self.as_ptr();
let offset = crate::ptr::align_offset(ptr, align_of::<U>());
offset > self.len() || {
let (_, rest) = self.split_at(offset);
let (us_len, _) = rest.align_to_offsets::<U>();
let middle = crate::ptr::slice_from_raw_parts(rest.as_ptr() as *const U, us_len);
crate::ub_checks::can_dereference(middle)
}
}
)]
//The following clause guarantees that middle is of maximum size within self
//If U or T are ZSTs, then middle has size zero, so we adapt the check in that case
#[ensures(|(prefix, _, suffix): &(&mut [T], &mut [U], &mut [T])|
((U::IS_ZST || T::IS_ZST) && prefix.len() == old(self.len())) || (
(prefix.len() * size_of::<T>() < align_of::<U>()) &&
(suffix.len() * size_of::<T>() < size_of::<U>())
)
)]
//Either align_to just returns self in the prefix, or the 3 returned slices
//should be sequential, contiguous, and have same total length as self
#[ensures(|(prefix, middle, suffix): &(&mut [T], &mut [U], &mut [T])|
prefix.as_ptr() == old(self.as_ptr()) &&
(prefix.len() == old(self.len()) || (
((prefix.as_ptr()).add(prefix.len()) as *const u8 == middle.as_ptr() as *const u8) &&
((middle.as_ptr()).add(middle.len()) as *const u8 == suffix.as_ptr() as *const u8) &&
((suffix.as_ptr()).add(suffix.len()) == old((self.as_ptr()).add(self.len())))
))
)]
pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
// Note that most of this function will be constant-evaluated,
if U::IS_ZST || T::IS_ZST {
Expand Down Expand Up @@ -5410,3 +5480,89 @@ unsafe impl GetDisjointMutIndex for range::RangeInclusive<usize> {
RangeInclusive::from(*self).is_overlapping(&RangeInclusive::from(*other))
}
}

#[cfg(kani)]
#[unstable(feature = "kani", issue = "none")]
mod verify {
use super::*;

//generates proof_of_contract harness for align_to given the T (src) and U (dst) types
macro_rules! proof_of_contract_for_align_to {
($harness:ident, $src:ty, $dst:ty) => {
#[kani::proof_for_contract(<[$src]>::align_to)]
fn $harness() {
const ARR_SIZE: usize = 100;
let src_arr: [$src; ARR_SIZE] = kani::any();
let src_slice = kani::slice::any_slice_of_array(&src_arr);
let dst_slice = unsafe { src_slice.align_to::<$dst>() };
}
};
}

//generates harnesses for align_to where T is a given src type and U is one of the main primitives
macro_rules! gen_align_to_harnesses {
($mod_name:ident, $src_type:ty) => {
mod $mod_name {
use super::*;

proof_of_contract_for_align_to!(align_to_u8, $src_type, u8);
proof_of_contract_for_align_to!(align_to_u16, $src_type, u16);
proof_of_contract_for_align_to!(align_to_u32, $src_type, u32);
proof_of_contract_for_align_to!(align_to_u64, $src_type, u64);
proof_of_contract_for_align_to!(align_to_u128, $src_type, u128);
proof_of_contract_for_align_to!(align_to_bool, $src_type, bool);
proof_of_contract_for_align_to!(align_to_char, $src_type, char);
proof_of_contract_for_align_to!(align_to_unit, $src_type, ());
}
};
}

gen_align_to_harnesses!(align_to_from_u8, u8);
gen_align_to_harnesses!(align_to_from_u16, u16);
gen_align_to_harnesses!(align_to_from_u32, u32);
gen_align_to_harnesses!(align_to_from_u64, u64);
gen_align_to_harnesses!(align_to_from_u128, u128);
gen_align_to_harnesses!(align_to_from_bool, bool);
gen_align_to_harnesses!(align_to_from_char, char);
gen_align_to_harnesses!(align_to_from_unit, ());

//generates proof_of_contract harness for align_to_mut given the T (src) and U (dst) types
macro_rules! proof_of_contract_for_align_to_mut {
($harness:ident, $src:ty, $dst:ty) => {
#[kani::proof_for_contract(<[$src]>::align_to_mut)]
fn $harness() {
const ARR_SIZE: usize = 100;
let mut src_arr: [$src; ARR_SIZE] = kani::any();
let src_slice = kani::slice::any_slice_of_array_mut(&mut src_arr);
let dst_slice = unsafe { src_slice.align_to_mut::<$dst>() };
}
};
}

//generates harnesses between a given src type and all the main primitives
macro_rules! gen_align_to_mut_harnesses {
($mod_name:ident, $src_type:ty) => {
mod $mod_name {
use super::*;

proof_of_contract_for_align_to_mut!(align_to_mut_u8, $src_type, u8);
proof_of_contract_for_align_to_mut!(align_to_mut_u16, $src_type, u16);
proof_of_contract_for_align_to_mut!(align_to_mut_u32, $src_type, u32);
proof_of_contract_for_align_to_mut!(align_to_mut_u64, $src_type, u64);
proof_of_contract_for_align_to_mut!(align_to_mut_u128, $src_type, u128);
proof_of_contract_for_align_to_mut!(align_to_mut_bool, $src_type, bool);
proof_of_contract_for_align_to_mut!(align_to_mut_char, $src_type, char);
proof_of_contract_for_align_to_mut!(align_to_mut_unit, $src_type, ());
}
};
}

gen_align_to_mut_harnesses!(align_to_mut_from_u8, u8);
gen_align_to_mut_harnesses!(align_to_mut_from_u16, u16);
gen_align_to_mut_harnesses!(align_to_mut_from_u32, u32);
gen_align_to_mut_harnesses!(align_to_mut_from_u64, u64);
gen_align_to_mut_harnesses!(align_to_mut_from_u128, u128);
gen_align_to_mut_harnesses!(align_to_mut_from_bool, bool);
gen_align_to_mut_harnesses!(align_to_mut_from_char, char);
gen_align_to_mut_harnesses!(align_to_mut_from_unit, ());
}
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