Rollup merge of rust-lang#131384 - saethlin:precondition-tests, r=ibraheemdev

Update precondition tests (especially for zero-size access to null)

I don't much like the current way I've updated the precondition check helpers, but I couldn't come up with anything better. Ideas welcome.

I've organized `tests/ui/precondition-checks` mostly with one file per function that has `assert_unsafe_precondition` in it, with revisions that check each precondition. The important new test is `tests/ui/precondition-checks/zero-size-null.rs`.

Author: matthiaskrgr

core/src/ascii/ascii_char.rs

@@ -506,7 +506,7 @@ impl AsciiChar {
     pub const unsafe fn digit_unchecked(d: u8) -> Self {
         assert_unsafe_precondition!(
             check_language_ub,
-            "`AsciiChar::digit_unchecked` input cannot exceed 9.",
+            "`ascii::Char::digit_unchecked` input cannot exceed 9.",
             (d: u8 = d) => d < 10
         );
 

core/src/intrinsics.rs

@@ -64,6 +64,7 @@
 #![allow(missing_docs)]
 
 use crate::marker::{DiscriminantKind, Tuple};
+use crate::mem::SizedTypeProperties;
 use crate::{ptr, ub_checks};
 
 pub mod mir;
@@ -3364,10 +3365,12 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
             size: usize = size_of::<T>(),
             align: usize = align_of::<T>(),
             count: usize = count,
-        ) =>
-        ub_checks::is_aligned_and_not_null(src, align)
-            && ub_checks::is_aligned_and_not_null(dst, align)
-            && ub_checks::is_nonoverlapping(src, dst, size, count)
+        ) => {
+            let zero_size = count == 0 || size == 0;
+            ub_checks::is_aligned_and_not_null(src, align, zero_size)
+                && ub_checks::is_aligned_and_not_null(dst, align, zero_size)
+                && ub_checks::is_nonoverlapping(src, dst, size, count)
+        }
     );
 
     // SAFETY: the safety contract for `copy_nonoverlapping` must be
@@ -3465,9 +3468,10 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
                 src: *const () = src as *const (),
                 dst: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
+                zero_size: bool = T::IS_ZST || count == 0,
             ) =>
-            ub_checks::is_aligned_and_not_null(src, align)
-                && ub_checks::is_aligned_and_not_null(dst, align)
+            ub_checks::is_aligned_and_not_null(src, align, zero_size)
+                && ub_checks::is_aligned_and_not_null(dst, align, zero_size)
         );
         copy(src, dst, count)
     }
@@ -3544,7 +3548,8 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
             (
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                zero_size: bool = T::IS_ZST || count == 0,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, zero_size)
         );
         write_bytes(dst, val, count)
     }

core/src/ptr/mod.rs

@@ -448,7 +448,7 @@
 
 use crate::cmp::Ordering;
 use crate::marker::FnPtr;
-use crate::mem::{self, MaybeUninit};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::{fmt, hash, intrinsics, ub_checks};
 
 mod alignment;
@@ -1165,10 +1165,12 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
             size: usize = size_of::<T>(),
             align: usize = align_of::<T>(),
             count: usize = count,
-        ) =>
-        ub_checks::is_aligned_and_not_null(x, align)
-            && ub_checks::is_aligned_and_not_null(y, align)
-            && ub_checks::is_nonoverlapping(x, y, size, count)
+        ) => {
+            let zero_size = size == 0 || count == 0;
+            ub_checks::is_aligned_and_not_null(x, align, zero_size)
+                && ub_checks::is_aligned_and_not_null(y, align, zero_size)
+                && ub_checks::is_nonoverlapping(x, y, size, count)
+        }
     );
 
     // Split up the slice into small power-of-two-sized chunks that LLVM is able
@@ -1278,7 +1280,8 @@ pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
             (
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                is_zst: bool = T::IS_ZST,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
         );
         mem::replace(&mut *dst, src)
     }
@@ -1430,7 +1433,8 @@ pub const unsafe fn read<T>(src: *const T) -> T {
             (
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                is_zst: bool = T::IS_ZST,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
         );
         crate::intrinsics::read_via_copy(src)
     }
@@ -1635,7 +1639,8 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
             (
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                is_zst: bool = T::IS_ZST,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::write_via_move(dst, src)
     }
@@ -1808,7 +1813,8 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
             (
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                is_zst: bool = T::IS_ZST,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::volatile_load(src)
     }
@@ -1887,7 +1893,8 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
             (
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
-            ) => ub_checks::is_aligned_and_not_null(addr, align)
+                is_zst: bool = T::IS_ZST,
+            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::volatile_store(dst, src);
     }

core/src/slice/raw.rs

@@ -132,7 +132,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
                 align: usize = align_of::<T>(),
                 len: usize = len,
             ) =>
-            ub_checks::is_aligned_and_not_null(data, align)
+            ub_checks::is_aligned_and_not_null(data, align, false)
                 && ub_checks::is_valid_allocation_size(size, len)
         );
         &*ptr::slice_from_raw_parts(data, len)
@@ -187,7 +187,7 @@ pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a m
                 align: usize = align_of::<T>(),
                 len: usize = len,
             ) =>
-            ub_checks::is_aligned_and_not_null(data, align)
+            ub_checks::is_aligned_and_not_null(data, align, false)
                 && ub_checks::is_valid_allocation_size(size, len)
         );
         &mut *ptr::slice_from_raw_parts_mut(data, len)

core/src/ub_checks.rs

@@ -109,15 +109,15 @@ pub(crate) const fn check_language_ub() -> bool {
     intrinsics::ub_checks() && const_eval_select((), comptime, runtime)
 }
 
-/// Checks whether `ptr` is properly aligned with respect to
-/// `align_of::<T>()`.
+/// Checks whether `ptr` is properly aligned with respect to the given alignment, and
+/// if `is_zst == false`, that `ptr` is not null.
 ///
 /// In `const` this is approximate and can fail spuriously. It is primarily intended
 /// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
 /// check is anyway not executed in `const`.
 #[inline]
-pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize) -> bool {
-    !ptr.is_null() && ptr.is_aligned_to(align)
+pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize, is_zst: bool) -> bool {
+    ptr.is_aligned_to(align) && (is_zst || !ptr.is_null())
 }
 
 #[inline]