Initial implementation of jemalloc-style arenas for the hardened malloc implementation:
github.com/AndroidHardeni
There's an independent slab region per arena, with threads statically assigned to an arena for now. It determines arena from address on free, just like size class.
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There are fully independent slab allocators for each size class, so locking is now per-size-class-per-arena. It's relatively fine grained. Each slab allocator uses an independent CSPRNG seeded from getrandom to avoid additional synchronization from extensive usage of randomness.
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This is the function mapping from an allocation address to the arena and size class:
github.com/AndroidHardeni
It will need to be optimized by making ARENA_SIZE into a power of 2, similar to how REAL_CLASS_REGION_SIZE is already a power of 2 with the default configuration values.