<vector> : Fix ASan annotations when clearing
#2464
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cbezault
commented
Jan 10, 2022
miscco
reviewed
Jan 11, 2022
<vector> : Correctly handle empty vectors with ASan annotations<vector> : Fix ASan annotations when clearing
* Make `_Modify_annotation(0)` a safe no-op.
+ Add a comment explaining why.
* Undo logic changes in `assign(n, val)` now that `_ASAN_VECTOR_MODIFY`
is always safe.
+ There are no potential gains from calling `clear()` as this function
begins by unconditionally calling `_My_data._Orphan_all();` and is
required to do so by the Standard.
* Comment `_ASAN_VECTOR_MODIFY` with `// negative when destroying elements`
when subtracting pointers, making it clear that the order of operands
is intentional.
* Similarly, undo logic changes in `assign(i, j)` and `assign(il)`.
They are also required to invalidate all iterators, so they can't
benefit from `clear()`'s optimization here.
* Ditto for `operator=(il)`. (The Standard isn't absolutely clear here,
but behaving identically to `assign(il)` seems obviously good.)
* Extend the `clear()` optimization to handle all empty vectors
(zero size), not just zero capacity.
+ Add a comment explaining why, and citing the Standard for why this
is allowed.
* Similarly undo logic changes in `_Move_assign_unequal_alloc()`.
* Add test coverage for calling `assign()` with an empty range of
input iterators.
StephanTLavavej
approved these changes
Jan 13, 2022
|
I approve of Stephan's changes. |
CaseyCarter
approved these changes
Jan 13, 2022
|
I have mirrored this to MSVC-PR-373503 ( |
miscco
approved these changes
Jan 13, 2022
|
Thanks for clearing out this bug! 🐞 🪄 😸 |
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_Modify_annotation(0)a no-op and add a comment explaining why: this avoids passingnullptrinto the ASan runtime when dealing with zero-capacity vectors._ASAN_VECTOR_MODIFYwith// negative when destroying elementswhen subtracting pointers, making it clear that the order of operands is intentional.clear()for empty vectors, and add a comment explaining why. This is permitted by the Standard, also explained in the comment.clear()'s use of_ASAN_VECTOR_MODIFY.