e694fb1312
This PR adds a conditional move following a heap bounds check through which the address to be accessed flows. This conditional move ensures that even if the branch is mispredicted (access is actually out of bounds, but speculation goes down in-bounds path), the acually accessed address is zero (a NULL pointer) rather than the out-of-bounds address. The mitigation is controlled by a flag that is off by default, but can be set by the embedding. Note that in order to turn it on by default, we would need to add conditional-move support to the current x86 backend; this does not appear to be present. Once the deprecated backend is removed in favor of the new backend, IMHO we should turn this flag on by default. Note that the mitigation is unneccessary when we use the "huge heap" technique on 64-bit systems, in which we allocate a range of virtual address space such that no 32-bit offset can reach other data. Hence, this only affects small-heap configurations.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.