Fix unsound use of Rooted<T> with RootKind::Traceable #514
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jschwe
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Signed-off-by: Josh Matthews <[email protected]>
sagudev
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Oct 28, 2024
Signed-off-by: Josh Matthews <[email protected]>
…nts TraceableTrace. Signed-off-by: Josh Matthews <[email protected]>
Signed-off-by: Josh Matthews <[email protected]>
sagudev
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| fn do_trace(&mut self, trc: *mut JSTracer) { | ||
| unsafe { | ||
| CallPropertyDescriptorTracer(trc, self); | ||
| } | ||
| unsafe fn do_trace(&mut self, trc: *mut JSTracer) { | ||
| CallPropertyDescriptorTracer(trc, self); | ||
| } |
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Actually unsafe block in unsafe fn will be the only correct way in the future: https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html, but that is not yet relevant.
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The existing implementation for
Rooted<T>is correct for most JS types that are rooted, but there's one significant case that is broken.Rooted<T>uses C++ template magic to change its base class depending on the type that it's templated over, and certain types that map toRootKind::Traceableend up with a vtable that contains a custom tracing implementation, while other types do not have any such vtable.These template shenanigans are very likely the reason why we have a handwritten
Rooted<T>definition, since bindgen is not able to handle this situation. This PR makes the following changes:Rooted<T>which is zero-sized for types that do not have Traceable RootKind valueTraceableTracetrait thatRooted<T>'s vtable delegates to, allowing implementers to write straightforward tracing implementations for their typesThese changes were verified by running the property_descriptor unit test with zealous GC enabled (ie. perform a GC every time there's an allocation) and the test no longer crashes after these changes are applied.