* Add default for getting chunk allocator state
Makes the API same between the two configurations.
* Reduce address space usage for Open Enclave
* Fix OE Pal concept
* Add support for Pal not to provide time.
The lazy return of pages to the OS uses a simple time
based heuristic. This enables a PAL to not support time,
and return the memory to a central pool immediately.
* Update src/backend/backend.h
Co-authored-by: Amaury Chamayou <amaury@xargs.fr>
Co-authored-by: Amaury Chamayou <amaury@xargs.fr>
This adds a way to periodically pool the PAL to see if any timers have
expired. Timers can be used to periodically provide callbacks to the
rest of snmalloc.
# Pagemap
The Pagemap now stores all the meta-data for the object allocation. The meta-data in the pagemap is effectively a triple of the sizeclass, the remote allocator, and a pointer to a 64 byte block of meta-data for this chunk of memory. By storing the pointer to a block, it allows the pagemap to handle multiple slab sizes without branching on the fast path. There is one entry in the pagemap per 16KiB of address space, but by using the same entry in the pagemap for 4 adjacent entries, then we can treat a 64KiB range can be treated as a single slab of allocations.
This change also means there is almost no capability amplification required by the implementation on CHERI for finding meta-data. The only amplification is required, when we change the way a chunk is used to a size of object allocation.
# Backend
There is a second major aspect of the refactor that there is now a narrow API that abstracts the Pagemap, PAL and address space management. This should better enable the compartmentalisation and makes it easier to produce alternative backends for various research directions. This is a template parameter that can be used to specialised by the front-end in different ways.
# Thread local state
The thread local state has been refactored into two components, one (called 'localalloc') that is stored directly in the TLS and is constant initialised, and one that is allocated in the address space (called 'coreallloc') which is lazily created and pooled.
# Difference
This removes Superslabs/Medium slabs as there meta-data is now part of the pagemap.
Summary of changes:
- Add a new PAL that doesn't allocate memory, which can be used with a
memory provider that is pre-initialised with a range of memory.
- Add a `NoAllocation` PAL property so that the methods on a PAL that
doesn't support dynamically reserving address space will never be
called and therefore don't need to be implemented.
- Slightly refactor the memory provider class so that it has a narrower
interface with LargeAlloc and is easier to proxy.
- Allow the address space manager and the memory provider to be
initialised with a range of memory.
This may eventually also remove the need for (or, at least, simplify)
the Open Enclave PAL.
This commit also ends up with a few other cleanups:
- The `malloc_useable_size` CMake test that checks whether the
parameter is const qualified was failing on FreeBSD where this
function is declared in `malloc_np.h` but where including
`malloc.h` raises an error. This should now be more robust.
- The BSD aligned PAL inherited from the BSD PAL, which does not
expose aligned allocation. This meant that it exposed both the
aligned and non-aligned allocation interfaces and so happily
accepted incorrect `constexpr` if blocks that expected one or
the other but accidentally required both to exist. The unaligned
function is now deleted so the same failures that appear in CI should
appear locally for anyone using this PAL.
