Instead, take a template parameter for the no-args init() method, so
that randomization can be disabled on StrictProvenance architectures
(CHERI), where we don't expect it to be useful, even when snmalloc is
being built to be otherwise paranoid.
Catch callsites up.
* Extend pagemap test
Check for possible overlap between heap and pagemap, but writing and
reading the heap.
* Return unalign memory from the pagemap
This commit allows the pagemap to return unaligned range of memory. This
means that bump allocation of multiple pagemaps doesn't
waste as much space.
* Rename to use Config, rather than StateHandle/Globals/Backend
* Make Backend a type on Config that contains the address space management implementation
* Make Ranges part of the Backend configuration, so we can reuse code for different ways of managing memory
* Pull the common chains of range definitions into separate files for reuse.
* Move PagemapEntry to CommonConfig
* Expose Pagemap through backend, so frontend doesn't see Pagemap directly
* Remove global Pal and use DefaultPal, where one is not pass explicitly.
Co-authored-by: David Chisnall <davidchisnall@users.noreply.github.com>
Co-authored-by: Nathaniel Filardo <105816689+nwf-msr@users.noreply.github.com>
See src/snmalloc/README.md for an explanation of the layers.
Some other cleanups on the way:
Fine-grained stats support is now gone.
It's been broken for two years, it depends on iostream (which then
causes linker failures with libstdc++) and it's collecting the wrong
stats for the new design. After discussion with @mjp41, it's better to
remove it and introduce new stats support later, rather than keep broken
code in the main branch.
Tracing was controlled with a preprocessor macro, now there's also a
CMake option.
Instead, tell the iostream to write out hex. This avoids the CHERI compiler
warning that we're turning a provenance-free value to a pointer.
Co-authored-by: Matthew Parkinson <mattpark@microsoft.com>
The Pal was providing policy for overallocating a block of memory to
achieve alignment make that part of the backend.
The backend should be responsible for layout policy.
This PR exposes a pagemap interface to specify ranges that are being
used. The overall invariant is that any memory in the address space
manager has the pagemap committed. This means that individual operations
do not need to commit entries.
This is important for Windows that does not support lazy commit. It is
also important if we want to PROT_NONE most of the pagemap to reduce the
risk of memory safety issues getting access to the pagemap.
There are minor changes to test to pull memory directly from the Pal.
There are also bug fixes in the pagemap tests.
The pagemap allocates it self directly either from
* the original fixed address range it is supplied, and returns the
remaining space after the pagemap is removed; or
* directly allocated from the PAL without using the address space
manager.
This change in layering is required for the next commit, which imposes
the invariant that the pagemap has been committed for all spaced managed
by the address space manager.
# 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.
This will let us use Pagemaps further down the dependency stack (specifically,
we're going to want a Pagemap inside the AddressSpaceManager) by letting us
manually tie the knot rather than rely on GlobalVirtual and
default_memory_provider() being defined by the time we want a Pagemap.
The pagemap was double incrementing the index level. This did not
exhibit in any use case of the pagemap as it only used 0 or 1 level of
intermediate index for all current use cases.
This commit fixes the bug, and adds a test that uses the pagemap in a
different configuration that has multiple levels of intermediate index
node.
