Skip to content

Commit

Permalink
Add harnesses for all public functions of Layout (#43)
Browse files Browse the repository at this point in the history 
Exercise all public member functions of `Layout` and assert properties
over the result. Some of those should, perhaps, become `ensures`
clauses.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

---------

Co-authored-by: Celina G. Val <celinval@amazon.com>
  • Loading branch information
@tautschnig @celinval
tautschnig and celinval authored Oct 2, 2024
1 parent 85a59bc commit 024d84b
Showing 1 changed file with 191 additions and 2 deletions.
193 changes: 191 additions & 2 deletions library/core/src/alloc/layout.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@
// collections, resulting in having to optimize down excess IR multiple times.
// Your performance intuition is useless. Run perf.

use safety::requires;
use safety::{ensures, requires};
use crate::error::Error;
use crate::ptr::{Alignment, NonNull};
use crate::{assert_unsafe_precondition, cmp, fmt, mem};
Expand Down Expand Up @@ -69,6 +69,10 @@ impl Layout {
#[rustc_const_stable(feature = "const_alloc_layout_size_align", since = "1.50.0")]
#[inline]
#[rustc_allow_const_fn_unstable(ptr_alignment_type)]
#[ensures(|result| result.is_err() || align.is_power_of_two())]
#[ensures(|result| result.is_err() || size <= isize::MAX as usize - (align - 1))]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().size() == size)]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align() == align)]
pub const fn from_size_align(size: usize, align: usize) -> Result<Self, LayoutError> {
if Layout::is_size_align_valid(size, align) {
// SAFETY: Layout::is_size_align_valid checks the preconditions for this call.
Expand Down Expand Up @@ -128,6 +132,8 @@ impl Layout {
#[inline]
#[rustc_allow_const_fn_unstable(ptr_alignment_type)]
#[requires(Layout::from_size_align(size, align).is_ok())]
#[ensures(|result| result.size() == size)]
#[ensures(|result| result.align() == align)]
pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
assert_unsafe_precondition!(
check_library_ub,
Expand Down Expand Up @@ -169,6 +175,8 @@ impl Layout {
#[rustc_const_stable(feature = "alloc_layout_const_new", since = "1.42.0")]
#[must_use]
#[inline]
#[ensures(|result| result.size() == mem::size_of::<T>())]
#[ensures(|result| result.align() == mem::align_of::<T>())]
pub const fn new<T>() -> Self {
let (size, align) = size_align::<T>();
// SAFETY: if the type is instantiated, rustc already ensures that its
Expand All @@ -184,6 +192,8 @@ impl Layout {
#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
#[must_use]
#[inline]
#[requires(mem::align_of_val(t).is_power_of_two())]
#[ensures(|result| result.align() == mem::align_of_val(t))]
pub const fn for_value<T: ?Sized>(t: &T) -> Self {
let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
// SAFETY: see rationale in `new` for why this is using the unsafe variant
Expand Down Expand Up @@ -220,6 +230,10 @@ impl Layout {
#[unstable(feature = "layout_for_ptr", issue = "69835")]
#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
#[must_use]
// TODO: we should try to capture the above constraints on T in a `requires` clause, and the
// metadata helpers from https://github.com/model-checking/verify-rust-std/pull/37 may be able
// to accomplish this.
#[ensures(|result| result.align().is_power_of_two())]
pub const unsafe fn for_value_raw<T: ?Sized>(t: *const T) -> Self {
// SAFETY: we pass along the prerequisites of these functions to the caller
let (size, align) = unsafe { (mem::size_of_val_raw(t), mem::align_of_val_raw(t)) };
Expand All @@ -237,6 +251,7 @@ impl Layout {
#[rustc_const_unstable(feature = "alloc_layout_extra", issue = "55724")]
#[must_use]
#[inline]
#[ensures(|result| result.is_aligned())]
pub const fn dangling(&self) -> NonNull<u8> {
// SAFETY: align is guaranteed to be non-zero
unsafe { NonNull::new_unchecked(crate::ptr::without_provenance_mut::<u8>(self.align())) }
Expand All @@ -258,6 +273,8 @@ impl Layout {
/// `align` violates the conditions listed in [`Layout::from_size_align`].
#[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
#[inline]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align() >= align)]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align().is_power_of_two())]
pub fn align_to(&self, align: usize) -> Result<Self, LayoutError> {
Layout::from_size_align(self.size(), cmp::max(self.align(), align))
}
Expand All @@ -283,6 +300,7 @@ impl Layout {
#[must_use = "this returns the padding needed, \
without modifying the `Layout`"]
#[inline]
#[ensures(|result| *result <= align)]
pub const fn padding_needed_for(&self, align: usize) -> usize {
let len = self.size();

Expand Down Expand Up @@ -319,6 +337,10 @@ impl Layout {
#[must_use = "this returns a new `Layout`, \
without modifying the original"]
#[inline]
#[ensures(|result| result.size() >= self.size())]
#[ensures(|result| result.align() == self.align())]
#[ensures(|result| result.size() % result.align() == 0)]
#[ensures(|result| self.size() + self.padding_needed_for(self.align()) == result.size())]
pub const fn pad_to_align(&self) -> Layout {
let pad = self.padding_needed_for(self.align());
// This cannot overflow. Quoting from the invariant of Layout:
Expand All @@ -341,6 +363,20 @@ impl Layout {
/// On arithmetic overflow, returns `LayoutError`.
#[unstable(feature = "alloc_layout_extra", issue = "55724")]
#[inline]
// for Kani (v0.54.0), the below modulo operation is too costly to prove (running into the
// 6-hours timeout on GitHub); we use a weaker postcondition instead
#[cfg_attr(not(kani),
ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().0.size() % n == 0))]
#[cfg_attr(kani,
ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().0.size() >= self.size()))]
// for Kani (v0.54.0), the below multiplication is too costly to prove (running into the
// 6-hours timeout on GitHub); we use a weaker postcondition instead
#[cfg_attr(not(kani),
ensures(|result| result.is_err() ||
result.as_ref().unwrap().0.size() == n * result.as_ref().unwrap().1))]
#[cfg_attr(kani,
ensures(|result| result.is_err() || n == 0 ||
result.as_ref().unwrap().0.size() >= result.as_ref().unwrap().1))]
pub fn repeat(&self, n: usize) -> Result<(Self, usize), LayoutError> {
// This cannot overflow. Quoting from the invariant of Layout:
// > `size`, when rounded up to the nearest multiple of `align`,
Expand Down Expand Up @@ -401,6 +437,10 @@ impl Layout {
/// ```
#[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
#[inline]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().0.align() == cmp::max(self.align(), next.align()))]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().0.size() >= self.size() + next.size())]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().1 >= self.size())]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().1 <= result.as_ref().unwrap().0.size())]
pub fn extend(&self, next: Self) -> Result<(Self, usize), LayoutError> {
let new_align = cmp::max(self.align, next.align);
let pad = self.padding_needed_for(next.align());
Expand All @@ -427,6 +467,13 @@ impl Layout {
/// On arithmetic overflow, returns `LayoutError`.
#[unstable(feature = "alloc_layout_extra", issue = "55724")]
#[inline]
// for Kani (v0.54.0), the below multiplication is too costly to prove (running into the
// 6-hours timeout on GitHub); we use a weaker postcondition instead
#[cfg_attr(not(kani),
ensures(|result| result.is_err() || result.as_ref().unwrap().size() == n * self.size()))]
#[cfg_attr(kani,
ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().size() >= self.size()))]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align() == self.align())]
pub fn repeat_packed(&self, n: usize) -> Result<Self, LayoutError> {
let size = self.size().checked_mul(n).ok_or(LayoutError)?;
// The safe constructor is called here to enforce the isize size limit.
Expand All @@ -441,6 +488,8 @@ impl Layout {
/// On arithmetic overflow, returns `LayoutError`.
#[unstable(feature = "alloc_layout_extra", issue = "55724")]
#[inline]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().size() == self.size() + next.size())]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align() == self.align())]
pub fn extend_packed(&self, next: Self) -> Result<Self, LayoutError> {
let new_size = self.size().checked_add(next.size()).ok_or(LayoutError)?;
// The safe constructor is called here to enforce the isize size limit.
Expand All @@ -454,6 +503,8 @@ impl Layout {
#[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
#[inline]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().size() == n * mem::size_of::<T>())]
#[ensures(|result| result.is_err() || result.as_ref().unwrap().align() == mem::align_of::<T>())]
pub const fn array<T>(n: usize) -> Result<Self, LayoutError> {
// Reduce the amount of code we need to monomorphize per `T`.
return inner(mem::size_of::<T>(), Alignment::of::<T>(), n);
Expand Down Expand Up @@ -520,15 +571,153 @@ impl fmt::Display for LayoutError {
mod verify {
use super::*;

impl kani::Arbitrary for Layout {
fn any() -> Self {
let align = kani::any::<Alignment>();
let size = kani::any_where(|s: &usize| *s <= isize::MAX as usize - (align.as_usize() - 1));
unsafe { Layout { size, align } }
}
}

// pub const fn from_size_align(size: usize, align: usize) -> Result<Self, LayoutError>
#[kani::proof_for_contract(Layout::from_size_align)]
pub fn check_from_size_align() {
let s = kani::any::<usize>();
let a = kani::any::<usize>();
let _ = Layout::from_size_align(s, a);
}

// pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self
#[kani::proof_for_contract(Layout::from_size_align_unchecked)]
pub fn check_from_size_align_unchecked() {
let s = kani::any::<usize>();
let a = kani::any::<usize>();
unsafe {
let _ = Layout::from_size_align_unchecked(s, a);
}
}

// pub const fn size(&self) -> usize
#[kani::proof]
pub fn check_size() {
let s = kani::any::<usize>();
let a = kani::any::<usize>();
kani::assume(Layout::from_size_align(s, a).is_ok());
unsafe {
let layout = Layout::from_size_align_unchecked(s, a);
assert_eq!(layout.size(), s);
assert_eq!(layout.align(), a);
}
}

// pub const fn align(&self) -> usize
#[kani::proof]
pub fn check_align() {
let layout = kani::any::<Layout>();
assert!(layout.align().is_power_of_two());
}

// pub const fn new<T>() -> Self
#[kani::proof_for_contract(Layout::new)]
pub fn check_new_i32() {
let _ = Layout::new::<i32>();
}

// pub const fn for_value<T: ?Sized>(t: &T) -> Self
#[kani::proof_for_contract(Layout::for_value)]
pub fn check_for_value_i32() {
let x = kani::any::<i32>();
let _ = Layout::for_value::<i32>(&x);
let array : [i32; 2] = [1, 2];
let _ = Layout::for_value::<[i32]>(&array[1 .. 1]);
let trait_ref: &dyn core::fmt::Debug = &x;
let _ = Layout::for_value::<dyn core::fmt::Debug>(trait_ref);
// TODO: the case of an extern type as unsized tail is not yet covered
}

// pub const unsafe fn for_value_raw<T: ?Sized>(t: *const T) -> Self
#[kani::proof_for_contract(Layout::for_value_raw)]
pub fn check_for_value_raw_i32() {
unsafe {
let x = kani::any::<i32>();
let _ = Layout::for_value_raw::<i32>(&x as *const i32);
let _ = Layout::for_value_raw::<[i32]>(&[] as *const [i32]);
let trait_ref: &dyn core::fmt::Debug = &x;
let _ = Layout::for_value_raw::<dyn core::fmt::Debug>(trait_ref);
// TODO: the case of an extern type as unsized tail is not yet covered
}
}

// pub const fn dangling(&self) -> NonNull<u8>
#[kani::proof_for_contract(Layout::dangling)]
pub fn check_dangling() {
let layout = kani::any::<Layout>();
let _ = layout.dangling();
}

// pub fn align_to(&self, align: usize) -> Result<Self, LayoutError>
#[kani::proof_for_contract(Layout::align_to)]
pub fn check_align_to() {
let layout = kani::any::<Layout>();
let a2 = kani::any::<usize>();
let _ = layout.align_to(a2);
}

// pub const fn padding_needed_for(&self, align: usize) -> usize
#[kani::proof_for_contract(Layout::padding_needed_for)]
pub fn check_padding_needed_for() {
let layout = kani::any::<Layout>();
let a2 = kani::any::<usize>();
if(a2.is_power_of_two() && a2 <= layout.align()) {
let _ = layout.padding_needed_for(a2);
}
}

// pub const fn pad_to_align(&self) -> Layout
#[kani::proof_for_contract(Layout::pad_to_align)]
pub fn check_pad_to_align() {
let layout = kani::any::<Layout>();
let _ = layout.pad_to_align();
}

// pub fn repeat(&self, n: usize) -> Result<(Self, usize), LayoutError>
#[kani::proof_for_contract(Layout::repeat)]
pub fn check_repeat() {
let layout = kani::any::<Layout>();
let n = kani::any::<usize>();
let _ = layout.repeat(n);
}

// pub fn extend(&self, next: Self) -> Result<(Self, usize), LayoutError>
#[kani::proof_for_contract(Layout::extend)]
pub fn check_extend() {
let layout = kani::any::<Layout>();
let layout2 = kani::any::<Layout>();
let _ = layout.extend(layout2);
}

// pub fn repeat_packed(&self, n: usize) -> Result<Self, LayoutError>
#[kani::proof_for_contract(Layout::repeat_packed)]
pub fn check_repeat_packed() {
let layout = kani::any::<Layout>();
let n = kani::any::<usize>();
let _ = layout.repeat_packed(n);
}

// pub fn extend_packed(&self, next: Self) -> Result<Self, LayoutError>
#[kani::proof_for_contract(Layout::extend_packed)]
pub fn check_extend_packed() {
let layout = kani::any::<Layout>();
let layout2 = kani::any::<Layout>();
let _ = layout.extend_packed(layout2);
}

// pub const fn array<T>(n: usize) -> Result<Self, LayoutError>
#[kani::proof_for_contract(Layout::array)]
pub fn check_array_i32() {
let n = kani::any::<usize>();
if let Ok(layout) = Layout::array::<i32>(n) {
assert!(layout.size() >= n * 4);
assert!(layout.align().is_power_of_two());
}
}
}

0 comments on commit 024d84b

Please sign in to comment.