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Rollup merge of #104568 - RalfJung:realloc, r=Amanieu

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clarify that realloc refreshes pointer provenance even when the allocation remains in-place

This [matches what C does](https://en.cppreference.com/w/c/memory/realloc):

> The original pointer ptr is invalidated and any access to it is undefined behavior (even if reallocation was in-place).

Cc `@rust-lang/wg-allocators`
This commit is contained in:
Matthias Krüger 2022-11-20 18:21:48 +01:00 • committed by GitHub
commit db5f005f35
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2 changed files with 11 additions and 7 deletions
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8
library/core/src/alloc/global.rs
View file

@ -208,9 +208,11 @@ pub unsafe trait GlobalAlloc {
///
/// If this returns a non-null pointer, then ownership of the memory block
/// referenced by `ptr` has been transferred to this allocator.
/// The memory may or may not have been deallocated, and should be
/// considered unusable. The new memory block is allocated with `layout`,
/// but with the `size` updated to `new_size`. This new layout should be
/// Any access to the old `ptr` is Undefined Behavior, even if the
/// allocation remained in-place. The newly returned pointer is the only valid pointer
/// for accessing this memory now.
/// The new memory block is allocated with `layout`,
/// but with the `size` updated to `new_size`. This new layout must be
/// used when deallocating the new memory block with `dealloc`. The range
/// `0..min(layout.size(), new_size)` of the new memory block is
/// guaranteed to have the same values as the original block.

10
library/core/src/alloc/mod.rs
View file

@ -169,8 +169,9 @@ pub unsafe trait Allocator {
/// this, the allocator may extend the allocation referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. The memory may or may not have been freed, and should be
/// considered unusable.
/// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
/// allocation was grown in-place. The newly returned pointer is the only valid pointer
/// for accessing this memory now.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.
@ -295,8 +296,9 @@ pub unsafe trait Allocator {
/// this, the allocator may shrink the allocation referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. The memory may or may not have been freed, and should be
/// considered unusable.
/// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
/// allocation was shrunk in-place. The newly returned pointer is the only valid pointer
/// for accessing this memory now.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.