Ouroboros is Unsound
Ouroboros has a soundness problem, but a fix has been implemented in 0.16.0.
In 0.15.0, Ouroboros works internally by creating a struct where all
uses of 'this are replaced by 'static. However, a recent addition to
Miri checks that references passed to functions are valid during the
entire execution of the function, even when those references are
passed inside a struct. This poses an issue for dropping
self-referencing values, as the reference becomes invalid during the
dropping process. Effectively, since self-referencing structs are
not allowed in vanilla Rust, there is no allowance for dropping data
during a function that has also been given a reference to that data.
There's usually no way to pass a and &a to the same function.
A fix was attempted, where the struct would be turned in to a raw
byte array and only transformed back into the underlying data type
inside each function. This is allowable as a reference can be
created and die over the body of a function, as long as the
reference was created inside the function. However, this is also
not sound if the original struct contains padding. There is no
way to initialize padding bytes to a known value that Miri will
accept, so when it is cast to an array some of the bytes contain
uninitialized values. This is not acceptable (despite the fact
that these bytes are never read) due to the potential for
optimizations that may read from the uninitialized bytes. Besides
which, this fix does not allow for template or constant parameters
as there is no way to check the size of a templated type without
giving specific, concrete values for the template parameters.
The final solution was to use this fix while wrapping the raw byte
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