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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [coroutines] Destroying a coroutine inside await_suspend with symmetric-transfer form hits asan use-after-free in non-optimized builds"
href="https://bugs.llvm.org/show_bug.cgi?id=47475">47475</a>
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<th>Summary</th>
<td>[coroutines] Destroying a coroutine inside await_suspend with symmetric-transfer form hits asan use-after-free in non-optimized builds
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>LLVM Codegen
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>lewissbaker@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>See <a href="https://godbolt.org/z/G7xM8G">https://godbolt.org/z/G7xM8G</a>
The problem seems to be with the code generated for symmetric-transfer style
suspend-points (where await_suspend() returns a coroutine_handle to be
resumed).
Under non-optimised builds the compiler generates code that materializes the
returned coroutine_handle as a temporary in before then calling
__builtin_coro_resume() on its address. However, it materializes the
coroutine_handle using storage from the coroutine-frame rather than
materializing it on the stack.
For coroutines that destroy themselves inside await_suspend(), this results in
a use-after-free, as the compiler is trying to write the materialized
coroutine_handle to the now-freed coroutine frame upon return of
await_suspend().
It should instead be materializing the returned coroutine_handle on the stack.
This is unlikely to be an issue under optimised builds as the returned
coroutine_handle is generally kept in a register.
This seems to have been an issue since Clang 7, when symmetric-transfer was
first introduced.</pre>
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