fix Box::into_unique effecitvely transmuting to a raw ptr #58429
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Centril
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fix Box::into_unique effecitvely transmuting to a raw ptr Miri/Stacked Borrows treat `Box` specially: they assert that it is unique, and tag it appropriately. However, currently, `Box::into_inner` is not aware of that and returns a raw pointer (wrapped in a `Unique`) that carries the same tag as the box, meaning it carries a `Uniq` tag. This leads to all sorts of problems when people use the raw pointer they get out of the `Unique` type. In the future, it'd be interesting to make `Unique` also carry some kind of uniqueness. In that case, something like this would instead be needed whenever a raw pointer is extracted from a `Unique`. However, that is out-of-scope for the current version of Stacked Borrows. So until then, this changes `into_unique` to perform a proper reference-to-raw-ptr-cast, which clears the tag.
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fix Box::into_unique effecitvely transmuting to a raw ptr Miri/Stacked Borrows treat `Box` specially: they assert that it is unique, and tag it appropriately. However, currently, `Box::into_inner` is not aware of that and returns a raw pointer (wrapped in a `Unique`) that carries the same tag as the box, meaning it carries a `Uniq` tag. This leads to all sorts of problems when people use the raw pointer they get out of the `Unique` type. In the future, it'd be interesting to make `Unique` also carry some kind of uniqueness. In that case, something like this would instead be needed whenever a raw pointer is extracted from a `Unique`. However, that is out-of-scope for the current version of Stacked Borrows. So until then, this changes `into_unique` to perform a proper reference-to-raw-ptr-cast, which clears the tag.
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Rollup of 19 pull requests Successful merges: - #57929 (Rustdoc remove old style files) - #57981 (Fix #57730) - #58074 (Stabilize slice_sort_by_cached_key) - #58196 (Add specific feature gate error for const-unstable features) - #58293 (Remove code for updating copyright years in generate-deriving-span-tests) - #58306 (Don't default on std crate when manipulating browser history) - #58359 (librustc_mir: use ? in impl_snapshot_for! macro) - #58395 (Instant::checked_duration_since) - #58429 (fix Box::into_unique effecitvely transmuting to a raw ptr) - #58433 (Update which libcore/liballoc tests Miri ignores, and document why) - #58438 (Use posix_spawn_file_actions_addchdir_np when possible) - #58440 (Whitelist the ARM v6 target-feature) - #58448 (rustdoc: mask `compiler_builtins` docs) - #58468 (split MaybeUninit into several features, expand docs a bit) - #58477 (Fix the syntax error in publish_toolstate.py) - #58479 (compile-pass test for #53606) - #58489 (Fix runtime error in generate-keyword-tests) - #58496 (Fix documentation for std::path::PathBuf::pop) - #58509 (Notify myself when Clippy toolstate changes)
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Rollup of 19 pull requests Successful merges: - #57929 (Rustdoc remove old style files) - #57981 (Fix #57730) - #58074 (Stabilize slice_sort_by_cached_key) - #58196 (Add specific feature gate error for const-unstable features) - #58293 (Remove code for updating copyright years in generate-deriving-span-tests) - #58306 (Don't default on std crate when manipulating browser history) - #58359 (librustc_mir: use ? in impl_snapshot_for! macro) - #58395 (Instant::checked_duration_since) - #58429 (fix Box::into_unique effecitvely transmuting to a raw ptr) - #58433 (Update which libcore/liballoc tests Miri ignores, and document why) - #58438 (Use posix_spawn_file_actions_addchdir_np when possible) - #58440 (Whitelist the ARM v6 target-feature) - #58448 (rustdoc: mask `compiler_builtins` docs) - #58468 (split MaybeUninit into several features, expand docs a bit) - #58479 (compile-pass test for #53606) - #58489 (Fix runtime error in generate-keyword-tests) - #58496 (Fix documentation for std::path::PathBuf::pop) - #58509 (Notify myself when Clippy toolstate changes) - #58521 (Fix tracking issue for error iterators)
Centril
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May 23, 2019
Box::into_unique: do the reborrow-to-raw *after* destroying the Box Currently we first "reborrow" the box to a raw pointer, and then `forget` it. When tracking raw pointers more strictly (something I am experimenting with locally in Miri), the "use" induced by passing the box to `forget` invalidates the previously created raw pointer. So adjust my hack from rust-lang#58429 to reorder the two operations.
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Miri/Stacked Borrows treat
Boxspecially: they assert that it is unique, and tag it appropriately. However, currently,Box::into_inneris not aware of that and returns a raw pointer (wrapped in aUnique) that carries the same tag as the box, meaning it carries aUniqtag. This leads to all sorts of problems when people use the raw pointer they get out of theUniquetype.In the future, it'd be interesting to make
Uniquealso carry some kind of uniqueness. In that case, something like this would instead be needed whenever a raw pointer is extracted from aUnique. However, that is out-of-scope for the current version of Stacked Borrows. So until then, this changesinto_uniqueto perform a proper reference-to-raw-ptr-cast, which clears the tag.