This is useful as codegen is nicer if we use size_t, but the semantics
is uint8_t, and is stored as that in many places in the metadata.
Ultimately should introduce a wrapper to check this invariant.
Will detect corruption caused by either
* Use-after-free
* Double-free
Neither is comprehensive. Full temporal safety is not possible.
This just aids with debugging.
Fix a false positive. The loops in the pagemap accessor are too
complicated for the static analyser to check, so it doesn't spot that a
non-null return is impossible.
This introduces a new `address_t` type and two new casts: `pointer_cast`
and `address_cast` for casting between an `address_t` and a pointer.
These should make it easier to audit the codebase for casts between
pointers and integers. In particular, the remaining `reinterpret_cast`s
and `pointer_cast`s should be the only places where we could perform
invalid pointer arithmetic.
Also adds a `pointer_offset` helper that adds an offset (in bytes) to a
pointer, preserving its original type. This is a sufficiently common
pattern that it seemed worthwhile to centralise it.
This is a generalisation of `std::nullptr_t` that allows non-0 values of
pointer-sized-but-not-a-pointer thing. `DLList` now takes an
`InvalidPointer`, `nullptr_t`, or some other compatible class as a
sentinel value instead of a `uintptr_t`.
We don't follow the pointers passed into the pagemap directly, but
instead use them to calculate indexs into the pagemap. Use uintptr_t
means it is easier to perform address arithmetic, and not have casts
back to void* everywhere.
Rather than unconditionally storing a pointer to the pagemap and
initialising this with a global, we now provide a choice of three
compile-time options for how the pagemap should be accessed.
If you're creating a new allocator and the pagemap comes from a library
that exports the pagemap accessor function but not the pagemap symbol,
you need to be able to replace this.
