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winch: Don't treat memory_reservation as a bound when minimum exceeds it - #14619
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Would it make sense to perhaps just remove this clause entirely? I'm having a tough time reasoning about the precise condition here and if it works just deleting the clause related to memory-reservation outright seems like a possibly simpler approach
…eeds it With `memory_may_move` disabled, Winch treated `memory_reservation` as an upper bound on accessible memory and turned any access whose offset + access size exceeded it into an unconditional trap. But when a memory's minimum size is larger than the reservation, the runtime sizes the allocation from the minimum instead, so in-bounds accesses past the reservation trapped spuriously. This removes the reservation clause, leaving `maximum_byte_size` as the only compile-time out-of-bounds check, which matches Cranelift. Accesses past the reservation now get the regular bounds check, which still traps when the memory can't grow past the reservation.
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That makes sense to me @alexcrichton, I was not sure as well on the original motivation for this check (and admittedly took me a bit to wrap my head around it). I've removed it in 90d3cdd; decided to keep the run test since there was none covering this feature. |
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Closes: #14588
With
memory_may_movedisabled, Winch treatedmemory_reservationas anupper bound on accessible memory and turned any access whose
offset + access size exceeded it into an unconditional trap. But when a
memory's minimum size is larger than the reservation, the runtime sizes
the allocation from the minimum instead, so in-bounds accesses past the
reservation trapped spuriously.
This removes the reservation clause, leaving
maximum_byte_sizeas theonly compile-time out-of-bounds check, which matches Cranelift. Accesses
past the reservation now get the regular bounds check, which still traps
when the memory can't grow past the reservation.