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Clarify is_inbounds docs #3974

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Merged
merged 2 commits into from
Apr 2, 2025
Merged

Clarify is_inbounds docs #3974

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bfc1f09
clarify is_inbounds docs
carolynzech Apr 1, 2025
17a0ad5
make verification failure explicit for unallocated memory case
carolynzech Apr 1, 2025
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18 changes: 8 additions & 10 deletions library/kani_core/src/mem.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -168,15 +168,13 @@ macro_rules! kani_mem {

/// Checks that `ptr` points to an allocation that can hold data of size calculated from `T`.
///
/// This will panic if `ptr` points to an invalid `non_null`
/// Returns `false` if:
/// - The computed size overflows.
/// - The computed size exceeds `isize::MAX`.
/// - The pointer is null (except for zero-sized types).
/// - The pointer references unallocated memory.
///
/// This function aligns with Rust's memory safety requirements, which restrict valid allocations
/// to sizes no larger than `isize::MAX`.
/// This function always returns `true` for ZSTs, since every pointer to a ZST is valid.
/// For non-ZSTs, this function will return `false` if `ptr` is null
/// or the size of the val pointed to exceeds `isize::MAX`.
/// Otherwise, it will return `true` if and only if `ptr` points to allocated memory
/// that can hold data of size calculated from `T`.
/// Note that Kani does not support reasoning about pointers to unallocated memory,
/// so if `ptr` does not point to allocated memory, verification will fail.
#[crate::kani::unstable_feature(
feature = "mem-predicates",
issue = 3946,
Expand All @@ -192,7 +190,7 @@ macro_rules! kani_mem {
} else {
// Note that this branch can't be tested in concrete execution as `is_read_ok` needs to be
// stubbed.
// We first assert that the data_ptr
// We first assert that the data_ptr points to a valid allocation.
let data_ptr = ptr as *const ();
if !unsafe { is_allocated(data_ptr, 0) } {
crate::kani::unsupported(
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