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Auto merge of #25300 - kballard:core-slice-overflow, r=Gankro

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core::slice was originally written to tolerate overflow (notably, with
slices of zero-sized elements), but it was never updated to use wrapping
arithmetic when overflow traps were added.

Also correctly handle the case of calling .nth() on an Iter with a
zero-sized element type. The iterator was assuming that the pointer
value of the returned reference was meaningful, but that's not true for
zero-sized elements.

Fixes #25016.
This commit is contained in:
bors 2015-05-12 14:39:31 +00:00
commit 2a5a320bab
2 changed files with 105 additions and 64 deletions
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109
src/libcore/slice.rs
View file

@ -140,7 +140,7 @@ impl<T> SliceExt for [T] {
assume(!p.is_null());
if mem::size_of::<T>() == 0 {
Iter {ptr: p,
end: (p as usize + self.len()) as *const T,
end: ((p as usize).wrapping_add(self.len())) as *const T,
_marker: marker::PhantomData}
} else {
Iter {ptr: p,
@ -277,7 +277,7 @@ impl<T> SliceExt for [T] {
assume(!p.is_null());
if mem::size_of::<T>() == 0 {
IterMut {ptr: p,
end: (p as usize + self.len()) as *mut T,
end: ((p as usize).wrapping_add(self.len())) as *mut T,
_marker: marker::PhantomData}
} else {
IterMut {ptr: p,
@ -632,35 +632,17 @@ fn size_from_ptr<T>(_: *const T) -> usize {
// Use macros to be generic over const/mut
//
// They require non-negative `$by` because otherwise the expression
// `(ptr as usize + $by)` would interpret `-1` as `usize::MAX` (and
// thus trigger a panic when overflow checks are on).
// Use this to do `$ptr + $by`, where `$by` is non-negative.
macro_rules! slice_add_offset {
macro_rules! slice_offset {
($ptr:expr, $by:expr) => {{
let ptr = $ptr;
if size_from_ptr(ptr) == 0 {
transmute(ptr as usize + $by)
transmute((ptr as isize).wrapping_add($by))
} else {
ptr.offset($by)
}
}};
}
// Use this to do `$ptr - $by`, where `$by` is non-negative.
macro_rules! slice_sub_offset {
($ptr:expr, $by:expr) => {{
let ptr = $ptr;
if size_from_ptr(ptr) == 0 {
transmute(ptr as usize - $by)
} else {
ptr.offset(-$by)
}
}};
}
macro_rules! slice_ref {
($ptr:expr) => {{
let ptr = $ptr;
@ -683,14 +665,16 @@ macro_rules! iterator {
#[inline]
fn next(&mut self) -> Option<$elem> {
// could be implemented with slices, but this avoids bounds checks
unsafe {
::intrinsics::assume(!self.ptr.is_null());
::intrinsics::assume(!self.end.is_null());
if self.ptr == self.end {
None
} else {
if self.ptr == self.end {
None
} else {
unsafe {
if mem::size_of::<T>() != 0 {
::intrinsics::assume(!self.ptr.is_null());
::intrinsics::assume(!self.end.is_null());
}
let old = self.ptr;
self.ptr = slice_add_offset!(self.ptr, 1);
self.ptr = slice_offset!(self.ptr, 1);
Some(slice_ref!(old))
}
}
@ -698,7 +682,7 @@ macro_rules! iterator {
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let diff = (self.end as usize) - (self.ptr as usize);
let diff = (self.end as usize).wrapping_sub(self.ptr as usize);
let size = mem::size_of::<T>();
let exact = diff / (if size == 0 {1} else {size});
(exact, Some(exact))
@ -726,13 +710,15 @@ macro_rules! iterator {
#[inline]
fn next_back(&mut self) -> Option<$elem> {
// could be implemented with slices, but this avoids bounds checks
unsafe {
::intrinsics::assume(!self.ptr.is_null());
::intrinsics::assume(!self.end.is_null());
if self.end == self.ptr {
None
} else {
self.end = slice_sub_offset!(self.end, 1);
if self.end == self.ptr {
None
} else {
unsafe {
self.end = slice_offset!(self.end, -1);
if mem::size_of::<T>() != 0 {
::intrinsics::assume(!self.ptr.is_null());
::intrinsics::assume(!self.end.is_null());
}
Some(slice_ref!(self.end))
}
}
@ -742,29 +728,29 @@ macro_rules! iterator {
}
macro_rules! make_slice {
($t: ty => $result: ty: $start: expr, $end: expr) => {{
let diff = $end as usize - $start as usize;
let len = if mem::size_of::<T>() == 0 {
diff
($start: expr, $end: expr) => {{
let start = $start;
let diff = ($end as usize).wrapping_sub(start as usize);
if size_from_ptr(start) == 0 {
// use a non-null pointer value
unsafe { from_raw_parts(1 as *const _, diff) }
} else {
diff / mem::size_of::<$t>()
};
unsafe {
from_raw_parts($start, len)
let len = diff / size_from_ptr(start);
unsafe { from_raw_parts(start, len) }
}
}}
}
macro_rules! make_mut_slice {
($t: ty => $result: ty: $start: expr, $end: expr) => {{
let diff = $end as usize - $start as usize;
let len = if mem::size_of::<T>() == 0 {
diff
($start: expr, $end: expr) => {{
let start = $start;
let diff = ($end as usize).wrapping_sub(start as usize);
if size_from_ptr(start) == 0 {
// use a non-null pointer value
unsafe { from_raw_parts_mut(1 as *mut _, diff) }
} else {
diff / mem::size_of::<$t>()
};
unsafe {
from_raw_parts_mut($start, len)
let len = diff / size_from_ptr(start);
unsafe { from_raw_parts_mut(start, len) }
}
}}
}
@ -787,14 +773,14 @@ impl<'a, T> Iter<'a, T> {
/// iterator can continue to be used while this exists.
#[unstable(feature = "core")]
pub fn as_slice(&self) -> &'a [T] {
make_slice!(T => &'a [T]: self.ptr, self.end)
make_slice!(self.ptr, self.end)
}
// Helper function for Iter::nth
fn iter_nth(&mut self, n: usize) -> Option<&'a T> {
match self.as_slice().get(n) {
Some(elem_ref) => unsafe {
self.ptr = slice_add_offset!(elem_ref as *const _, 1);
self.ptr = slice_offset!(self.ptr, (n as isize).wrapping_add(1));
Some(slice_ref!(elem_ref))
},
None => {
@ -827,12 +813,7 @@ impl<'a, T> RandomAccessIterator for Iter<'a, T> {
fn idx(&mut self, index: usize) -> Option<&'a T> {
unsafe {
if index < self.indexable() {
if mem::size_of::<T>() == 0 {
// Use a non-null pointer value
Some(&mut *(1 as *mut _))
} else {
Some(transmute(self.ptr.offset(index as isize)))
}
Some(slice_ref!(self.ptr.offset(index as isize)))
} else {
None
}
@ -860,14 +841,14 @@ impl<'a, T> IterMut<'a, T> {
/// restricted lifetimes that do not consume the iterator.
#[unstable(feature = "core")]
pub fn into_slice(self) -> &'a mut [T] {
make_mut_slice!(T => &'a mut [T]: self.ptr, self.end)
make_mut_slice!(self.ptr, self.end)
}
// Helper function for IterMut::nth
fn iter_nth(&mut self, n: usize) -> Option<&'a mut T> {
match make_mut_slice!(T => &'a mut [T]: self.ptr, self.end).get_mut(n) {
match make_mut_slice!(self.ptr, self.end).get_mut(n) {
Some(elem_ref) => unsafe {
self.ptr = slice_add_offset!(elem_ref as *mut _, 1);
self.ptr = slice_offset!(self.ptr, (n as isize).wrapping_add(1));
Some(slice_ref!(elem_ref))
},
None => {

60
src/test/run-pass/slice-of-zero-size-elements.rs Normal file
View file

@ -0,0 +1,60 @@
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// compile-flags: -C debug-assertions
#![feature(core)]
use std::slice;
fn foo<T>(v: &[T]) -> Option<&[T]> {
let mut it = v.iter();
for _ in 0..5 {
let _ = it.next();
}
Some(it.as_slice())
}
fn foo_mut<T>(v: &mut [T]) -> Option<&mut [T]> {
let mut it = v.iter_mut();
for _ in 0..5 {
let _ = it.next();
}
Some(it.into_slice())
}
pub fn main() {
// In a slice of zero-size elements the pointer is meaningless.
// Ensure iteration still works even if the pointer is at the end of the address space.
let slice: &[()] = unsafe { slice::from_raw_parts(-5isize as *const (), 10) };
assert_eq!(slice.len(), 10);
assert_eq!(slice.iter().count(), 10);
// .nth() on the iterator should also behave correctly
let mut it = slice.iter();
assert!(it.nth(5).is_some());
assert_eq!(it.count(), 4);
// Converting Iter to a slice should never have a null pointer
assert!(foo(slice).is_some());
// Test mutable iterators as well
let slice: &mut [()] = unsafe { slice::from_raw_parts_mut(-5isize as *mut (), 10) };
assert_eq!(slice.len(), 10);
assert_eq!(slice.iter_mut().count(), 10);
{
let mut it = slice.iter_mut();
assert!(it.nth(5).is_some());
assert_eq!(it.count(), 4);
}
assert!(foo_mut(slice).is_some())
}