From 0c41c3414c0e89ccb19310a4ec423ac83a48f039 Mon Sep 17 00:00:00 2001 From: Ben Kimock Date: Mon, 7 Oct 2024 19:34:13 -0400 Subject: [PATCH] Allow zero-size reads/writes on null pointers --- library/core/src/intrinsics.rs | 19 ++++++++++++------- library/core/src/ptr/mod.rs | 21 +++++++++++++-------- library/core/src/slice/raw.rs | 4 ++-- library/core/src/ub_checks.rs | 4 ++-- 4 files changed, 29 insertions(+), 19 deletions(-) diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs index d7a2f1909ca..d76b7ca66cc 100644 --- a/library/core/src/intrinsics.rs +++ b/library/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; @@ -3311,10 +3312,12 @@ pub const fn ptr_metadata + ?Sized, M>(_ptr: *cons size: usize = size_of::(), align: usize = align_of::(), 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 @@ -3412,9 +3415,10 @@ pub const fn ptr_metadata + ?Sized, M>(_ptr: *cons src: *const () = src as *const (), dst: *mut () = dst as *mut (), align: usize = align_of::(), + 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) } @@ -3491,7 +3495,8 @@ pub const fn ptr_metadata + ?Sized, M>(_ptr: *cons ( addr: *const () = dst as *const (), align: usize = align_of::(), - ) => 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) } diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs index 67f1b0cd16d..53ca5a7f198 100644 --- a/library/core/src/ptr/mod.rs +++ b/library/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 @@ macro_rules! attempt_swap_as_chunks { size: usize = size_of::(), align: usize = align_of::(), 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 @@ -1277,7 +1279,8 @@ macro_rules! attempt_swap_as_chunks { ( addr: *const () = dst as *const (), align: usize = align_of::(), - ) => 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) } @@ -1806,7 +1809,8 @@ pub unsafe fn read_volatile(src: *const T) -> T { ( addr: *const () = src as *const (), align: usize = align_of::(), - ) => 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) } @@ -1885,7 +1889,8 @@ pub unsafe fn write_volatile(dst: *mut T, src: T) { ( addr: *mut () = dst as *mut (), align: usize = align_of::(), - ) => 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); } diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs index 84e916b9a84..27bbadf7c89 100644 --- a/library/core/src/slice/raw.rs +++ b/library/core/src/slice/raw.rs @@ -132,7 +132,7 @@ align: usize = align_of::(), 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 @@ align: usize = align_of::(), 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) diff --git a/library/core/src/ub_checks.rs b/library/core/src/ub_checks.rs index c1a8c34539e..2ea30e77609 100644 --- a/library/core/src/ub_checks.rs +++ b/library/core/src/ub_checks.rs @@ -116,8 +116,8 @@ const fn comptime() -> bool { /// 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 { + if is_zst { ptr.is_aligned_to(align) } else { !ptr.is_null() && ptr.is_aligned_to(align) } } #[inline]