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Avoid forming references to an uninitialized memory in DroplessArena 

Return a pointer from `alloc_raw` instead of a slice. There is no
practical use for slice as a return type and changing it to a pointer
avoids forming references to an uninitialized memory.
This commit is contained in:
Tomasz Miąsko 2020-06-14 00:00:00 +00:00
parent c0c3327ade
commit 1f0895162b
2 changed files with 12 additions and 15 deletions
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25
src/librustc_arena/lib.rs
View File

@ -367,7 +367,7 @@ impl DroplessArena {
/// current memory chunk. Returns `None` if there is no free space left to
/// satisfy the request.
#[inline]
fn alloc_raw_without_grow(&self, bytes: usize, align: usize) -> Option<&mut [u8]> {
fn alloc_raw_without_grow(&self, bytes: usize, align: usize) -> Option<*mut u8> {
let ptr = self.ptr.get() as usize;
let end = self.end.get() as usize;
// The allocation request fits into the current chunk iff:
@ -383,14 +383,14 @@ impl DroplessArena {
let new_ptr = aligned.checked_add(bytes)?;
if new_ptr <= end {
self.ptr.set(new_ptr as *mut u8);
unsafe { Some(slice::from_raw_parts_mut(aligned as *mut u8, bytes)) }
Some(aligned as *mut u8)
} else {
None
}
}
#[inline]
pub fn alloc_raw(&self, bytes: usize, align: usize) -> &mut [u8] {
pub fn alloc_raw(&self, bytes: usize, align: usize) -> *mut u8 {
assert!(bytes != 0);
loop {
if let Some(a) = self.alloc_raw_without_grow(bytes, align) {
@ -406,7 +406,7 @@ impl DroplessArena {
pub fn alloc<T>(&self, object: T) -> &mut T {
assert!(!mem::needs_drop::<T>());
let mem = self.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut _ as *mut T;
let mem = self.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut T;
unsafe {
// Write into uninitialized memory.
@ -431,13 +431,11 @@ impl DroplessArena {
assert!(mem::size_of::<T>() != 0);
assert!(!slice.is_empty());
let mem = self.alloc_raw(slice.len() * mem::size_of::<T>(), mem::align_of::<T>()) as *mut _
as *mut T;
let mem = self.alloc_raw(slice.len() * mem::size_of::<T>(), mem::align_of::<T>()) as *mut T;
unsafe {
let arena_slice = slice::from_raw_parts_mut(mem, slice.len());
arena_slice.copy_from_slice(slice);
arena_slice
mem.copy_from_nonoverlapping(slice.as_ptr(), slice.len());
slice::from_raw_parts_mut(mem, slice.len())
}
}
@ -480,7 +478,7 @@ impl DroplessArena {
return &mut [];
}
let size = len.checked_mul(mem::size_of::<T>()).unwrap();
let mem = self.alloc_raw(size, mem::align_of::<T>()) as *mut _ as *mut T;
let mem = self.alloc_raw(size, mem::align_of::<T>()) as *mut T;
unsafe { self.write_from_iter(iter, len, mem) }
}
(_, _) => {
@ -495,7 +493,7 @@ impl DroplessArena {
let len = vec.len();
let start_ptr = self
.alloc_raw(len * mem::size_of::<T>(), mem::align_of::<T>())
as *mut _ as *mut T;
as *mut T;
vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
vec.set_len(0);
slice::from_raw_parts_mut(start_ptr, len)
@ -539,8 +537,7 @@ pub struct DropArena {
impl DropArena {
#[inline]
pub unsafe fn alloc<T>(&self, object: T) -> &mut T {
let mem =
self.arena.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut _ as *mut T;
let mem = self.arena.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut T;
// Write into uninitialized memory.
ptr::write(mem, object);
let result = &mut *mem;
@ -563,7 +560,7 @@ impl DropArena {
let start_ptr = self
.arena
.alloc_raw(len.checked_mul(mem::size_of::<T>()).unwrap(), mem::align_of::<T>())
as *mut _ as *mut T;
as *mut T;
let mut destructors = self.destructors.borrow_mut();
// Reserve space for the destructors so we can't panic while adding them

2
src/librustc_middle/ty/list.rs
View File

@ -55,7 +55,7 @@ impl<T: Copy> List<T> {
.dropless
.alloc_raw(size, cmp::max(mem::align_of::<T>(), mem::align_of::<usize>()));
unsafe {
let result = &mut *(mem.as_mut_ptr() as *mut List<T>);
let result = &mut *(mem as *mut List<T>);
// Write the length
result.len = slice.len();