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Challenge 2: Kani contracts for raw-pointer core::intrinsics #643

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4389523
Challenge 2: Kani contracts for raw-pointer core::intrinsics
sankalpsthakur Aug 20, 2026
cce83da
Challenge 2: add raw-pointer intrinsic harness module
sankalpsthakur Aug 20, 2026
8ee4393
Challenge 2: rustfmt library files for upstream_test
sankalpsthakur Aug 20, 2026
9b99282
Challenge 2: fix Kani contract harnesses for raw-pointer intrinsics
sankalpsthakur Aug 20, 2026
a71f6bd
Challenge 2: rustfmt after Kani contract fixes
sankalpsthakur Aug 20, 2026
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35 changes: 35 additions & 0 deletions library/core/src/fmt/num.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,10 @@
//! Integer and floating-point number formatting

use safety::requires;

use crate::fmt::NumBuffer;
#[cfg(kani)]
use crate::kani;
use crate::mem::MaybeUninit;
use crate::num::fmt as numfmt;
use crate::{fmt, str};
Expand Down Expand Up @@ -180,6 +184,8 @@ macro_rules! impl_Display {
reason = "specialized method meant to only be used by `SpecToString` implementation",
issue = "none"
)]
#[requires(buf.len() >= Self::MAX.ilog10() as usize + 1)]
#[cfg_attr(kani, kani::modifies(buf))]
pub unsafe fn _fmt<'a>(self, buf: &'a mut [MaybeUninit::<u8>]) -> &'a str {
// SAFETY: `buf` will always be big enough to contain all digits.
let offset = unsafe { self._fmt_inner(buf) };
Expand Down Expand Up @@ -596,13 +602,17 @@ impl_Debug! {
#[cfg(any(target_pointer_width = "64", target_arch = "wasm32"))]
mod imp {
use super::*;
#[cfg(kani)]
use crate::kani;
impl_Display!(i8, u8, i16, u16, i32, u32, i64, u64, isize, usize; as u64 into display_u64);
impl_Exp!(i8, u8, i16, u16, i32, u32, i64, u64, isize, usize; as u64 into exp_u64);
}

#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
mod imp {
use super::*;
#[cfg(kani)]
use crate::kani;
impl_Display!(i8, u8, i16, u16, i32, u32, isize, usize; as u32 into display_u32);
impl_Display!(i64, u64; as u64 into display_u64);

Expand Down Expand Up @@ -645,6 +655,8 @@ impl u128 {
reason = "specialized method meant to only be used by `SpecToString` implementation",
issue = "none"
)]
#[requires(buf.len() >= U128_MAX_DEC_N)]
#[cfg_attr(kani, kani::modifies(buf))]
pub unsafe fn _fmt<'a>(self, buf: &'a mut [MaybeUninit<u8>]) -> &'a str {
// SAFETY: `buf` will always be big enough to contain all digits.
let offset = unsafe { self._fmt_inner(buf) };
Expand Down Expand Up @@ -862,3 +874,26 @@ fn div_rem_1e16(n: u128) -> (u128, u64) {
let rem = n - quot * D;
(quot, rem as u64)
}

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

/// Successor of the former `fmt::num::parse_u64_into` (removed when decimal
/// formatting was rewritten). `_fmt` still fills a `MaybeUninit<u8>` buffer
/// with ASCII digits of a `u64`.
#[cfg(not(feature = "optimize_for_size"))]
#[kani::proof_for_contract(u64::_fmt)]
#[kani::unwind(21)]
fn check_u64_fmt_parse_u64_into_successor() {
let n: u64 = kani::any();
const MAX: usize = 20;
let mut buf = [MaybeUninit::<u8>::uninit(); MAX];
let s = unsafe { n._fmt(&mut buf) };
assert!(s.len() <= MAX);
assert!(!s.is_empty());
}
}
89 changes: 18 additions & 71 deletions library/core/src/intrinsics/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2753,10 +2753,8 @@ pub const fn contract_check_ensures<C: Fn(&Ret) -> bool + Copy, Ret>(
#[rustc_intrinsic]
// VTable pointers must be valid for dereferencing at least 3 `usize` (size, alignment and drop):
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/166>
// TODO: we can no longer do this given https://github.com/model-checking/kani/issues/3325 (this
// function used to have a dummy body, but no longer has since
// https://github.com/rust-lang/rust/pull/137489 has been merged).
// #[requires(ub_checks::can_dereference(_ptr as *const [usize; 3]))]
// Contracts cannot sit on this bodyless intrinsic (kani#3325); see
// `vtable_size_wrapper` in `verify_memory.rs`.
pub unsafe fn vtable_size(_ptr: *const ()) -> usize;

/// The intrinsic will return the alignment stored in that vtable.
Expand All @@ -2769,10 +2767,8 @@ pub unsafe fn vtable_size(_ptr: *const ()) -> usize;
#[rustc_intrinsic]
// VTable pointers must be valid for dereferencing at least 3 `usize` (size, alignment and drop):
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/166>
// TODO: we can no longer do this given https://github.com/model-checking/kani/issues/3325 (this
// function used to have a dummy body, but no longer has since
// https://github.com/rust-lang/rust/pull/137489 has been merged).
// #[requires(ub_checks::can_dereference(_ptr as *const [usize; 3]))]
// Contracts cannot sit on this bodyless intrinsic (kani#3325); see
// `vtable_align_wrapper` in `verify_memory.rs`.
pub unsafe fn vtable_align(_ptr: *const ()) -> usize;

/// The size of a type in bytes.
Expand Down Expand Up @@ -2960,7 +2956,9 @@ fn check_copy_untyped<T>(src: *const T, dst: *mut T, count: usize) -> bool {
// them and check it. Using quantifiers would not add value as we can rely on the solver to
// pick an uninitialized element if such an element exists.
let elem = kani::any_where(|val: &usize| *val < count);
let src_data = src as *const u8;
// Offset both sides by `elem`. Comparing `dst[elem]` against `src[0]`
// is wrong when initialization differs across elements.
let src_data = unsafe { src.add(elem) } as *const u8;
let dst_data = unsafe { dst.add(elem) } as *const u8;
ub_checks::can_dereference(unsafe { src_data.add(byte) })
== ub_checks::can_dereference(unsafe { dst_data.add(byte) })
Expand All @@ -2981,14 +2979,8 @@ fn check_copy_untyped<T>(src: *const T, dst: *mut T, count: usize) -> bool {
#[rustc_nounwind]
#[rustc_intrinsic]
// Copy is "untyped".
// TODO: we can no longer do this given https://github.com/model-checking/kani/issues/3325 (this
// function used to have a dummy body, but no longer has)
// #[cfg_attr(kani, kani::modifies(crate::ptr::slice_from_raw_parts(dst, count)))]
// #[requires(!count.overflowing_mul(size_of::<T>()).1
// && ub_checks::can_dereference(core::ptr::slice_from_raw_parts(src as *const crate::mem::MaybeUninit<T>, count))
// && ub_checks::can_write(core::ptr::slice_from_raw_parts_mut(dst, count))
// && ub_checks::maybe_is_nonoverlapping(src as *const (), dst as *const (), size_of::<T>(), count))]
// #[ensures(|_| { check_copy_untyped(src, dst, count)})]
// Contracts cannot sit on this bodyless intrinsic (kani#3325); see
// `copy_nonoverlapping_wrapper` in `verify_memory.rs`.
pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);

/// This is an accidentally-stable alias to [`ptr::copy`]; use that instead.
Expand All @@ -3000,13 +2992,8 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
#[rustc_nounwind]
#[rustc_intrinsic]
// TODO: we can no longer do this given https://github.com/model-checking/kani/issues/3325 (this
// function used to have a dummy body, but no longer has)
// #[requires(!count.overflowing_mul(size_of::<T>()).1
// && ub_checks::can_dereference(core::ptr::slice_from_raw_parts(src as *const crate::mem::MaybeUninit<T>, count))
// && ub_checks::can_write(core::ptr::slice_from_raw_parts_mut(dst, count)))]
// #[ensures(|_| { check_copy_untyped(src, dst, count) })]
// #[cfg_attr(kani, kani::modifies(crate::ptr::slice_from_raw_parts(dst, count)))]
// Contracts cannot sit on this bodyless intrinsic (kani#3325); see
// `copy_wrapper` in `verify_memory.rs`.
pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);

/// This is an accidentally-stable alias to [`ptr::write_bytes`]; use that instead.
Expand All @@ -3018,14 +3005,8 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
#[rustc_nounwind]
#[rustc_intrinsic]
// TODO: we can no longer do this given https://github.com/model-checking/kani/issues/3325 (this
// function used to have a dummy body, but no longer has)
// #[requires(!count.overflowing_mul(size_of::<T>()).1
// && ub_checks::can_write(core::ptr::slice_from_raw_parts_mut(dst, count)))]
// #[requires(ub_checks::maybe_is_aligned_and_not_null(dst as *const (), align_of::<T>(), T::IS_ZST || count == 0))]
// #[ensures(|_|
// ub_checks::can_dereference(crate::ptr::slice_from_raw_parts(dst as *const u8, count * size_of::<T>())))]
// #[cfg_attr(kani, kani::modifies(crate::ptr::slice_from_raw_parts(dst, count)))]
// Contracts cannot sit on this bodyless intrinsic (kani#3325); see
// `write_bytes_wrapper` in `verify_memory.rs`.
pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize);

/// Returns the minimum (IEEE 754-2008 minNum) of two `f16` values.
Expand Down Expand Up @@ -3497,33 +3478,7 @@ mod verify {
});
}

// #[kani::proof_for_contract(copy)]
// fn check_copy() {
// run_with_arbitrary_ptrs::<char>(|src, dst| unsafe { copy(src, dst, kani::any()) });
// }

// #[kani::proof_for_contract(copy_nonoverlapping)]
// fn check_copy_nonoverlapping() {
// // Note: cannot use `ArbitraryPointer` here.
// // The `ArbitraryPtr` will arbitrarily initialize memory by indirectly invoking
// // `copy_nonoverlapping`.
// // Kani contract checking would fail due to existing restriction on calls to
// // the function under verification.
// let gen_any_ptr = |buf: &mut [MaybeUninit<char>; 100]| -> *mut char {
// let base = buf.as_mut_ptr() as *mut u8;
// base.wrapping_add(kani::any_where(|offset: &usize| *offset < 400)) as *mut char
// };
// let mut buffer1 = [MaybeUninit::<char>::uninit(); 100];
// for i in 0..100 {
// if kani::any() {
// buffer1[i] = MaybeUninit::new(kani::any());
// }
// }
// let mut buffer2 = [MaybeUninit::<char>::uninit(); 100];
// let src = gen_any_ptr(&mut buffer1);
// let dst = if kani::any() { gen_any_ptr(&mut buffer2) } else { gen_any_ptr(&mut buffer1) };
// unsafe { copy_nonoverlapping(src, dst, kani::any()) }
// }
// Copy / copy_nonoverlapping / write_bytes proofs: see `verify_memory.rs`.

//We need this wrapper because transmute_unchecked is an intrinsic, for which Kani does
//not currently support contracts (https://github.com/model-checking/kani/issues/3345)
Expand Down Expand Up @@ -4116,18 +4071,6 @@ mod verify {
gen_compound_harnesses!(arr_mod, [u8; 2]);
gen_compound_harnesses!(struct_mod, u8_struct);

// FIXME: Enable this harness once <https://github.com/model-checking/kani/issues/90> is fixed.
// Harness triggers a spurious failure when writing 0 bytes to an invalid memory location,
// which is a safe operation.
#[cfg(not(kani))]
#[kani::proof_for_contract(write_bytes)]
fn check_write_bytes() {
let mut generator = PointerGenerator::<100>::new();
let ArbitraryPointer { ptr, status, .. } = generator.any_alloc_status::<char>();
kani::assume(supported_status(status));
unsafe { write_bytes(ptr, kani::any(), kani::any()) };
}

fn run_with_arbitrary_ptrs<T: Arbitrary>(harness: impl Fn(*mut T, *mut T)) {
let mut generator1 = PointerGenerator::<100>::new();
let mut generator2 = PointerGenerator::<100>::new();
Expand All @@ -4151,3 +4094,7 @@ mod verify {
status != AllocationStatus::Dangling && status != AllocationStatus::DeadObject
}
}

#[cfg(kani)]
#[unstable(feature = "kani", issue = "none")]
mod verify_memory;
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