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Rollup merge of #37708 - oli-obk:box_free, r=eddyb

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change the `box_free` lang item to accept pointers to unsized types

in miri we use the `box_free` lang item as the destructor for `Box` objects, since the function's api matches that of an `fn drop(&mut self)` in a hypothetical `impl<T: ?Sized> Drop for Box<T>` exactly.

This works fine except if we insert a check in the `size_of` intrinsic to ensure that it is only called with sized types, since the `box_free` lang item calls that intrinsic.

cc @eddyb

no clue who to r? here, probably lang team?
This commit is contained in:
Eduard-Mihai Burtescu 2016-11-12 10:38:44 +02:00 committed by GitHub
commit 69717bbded
2 changed files with 7 additions and 6 deletions
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4
src/doc/book/lang-items.md
View File

@ -46,8 +46,8 @@ unsafe fn deallocate(ptr: *mut u8, _size: usize, _align: usize) {
}
#[lang = "box_free"]
unsafe fn box_free<T>(ptr: *mut T) {
deallocate(ptr as *mut u8, ::core::mem::size_of::<T>(), ::core::mem::align_of::<T>());
unsafe fn box_free<T: ?Sized>(ptr: *mut T) {
deallocate(ptr as *mut u8, ::core::mem::size_of_val(&*ptr), ::core::mem::align_of_val(&*ptr));
}
#[start]

9
src/liballoc/heap.rs
View File

@ -17,7 +17,7 @@
use core::{isize, usize};
#[cfg(not(test))]
use core::intrinsics::{min_align_of, size_of};
use core::intrinsics::{min_align_of_val, size_of_val};
#[allow(improper_ctypes)]
extern "C" {
@ -152,11 +152,12 @@ unsafe fn exchange_free(ptr: *mut u8, old_size: usize, align: usize) {
#[cfg(not(test))]
#[lang = "box_free"]
#[inline]
unsafe fn box_free<T>(ptr: *mut T) {
let size = size_of::<T>();
unsafe fn box_free<T: ?Sized>(ptr: *mut T) {
let size = size_of_val(&*ptr);
let align = min_align_of_val(&*ptr);
// We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
if size != 0 {
deallocate(ptr as *mut u8, size, min_align_of::<T>());
deallocate(ptr as *mut u8, size, align);
}
}