This is a draft of the upcoming next-gen malloc
implementation for
musl libc. It is essentially feature-complete, but is not yet
integrated with musl and lacks some additional hardening and
optimizations that the final version is expected to include.
The included Makefile
builds static and shared library files that
programs can link with, or use with LD_PRELOAD
(for the shared
version).
This allocator organizes memory dynamically into small slab-style groups of up to 32 identical-size allocation units with status controlled by bitmasks, and utilizes a mix of in-band and out-of-band metadata to isolate sensitive state from regions easily accessible through out-of-bounds writes, while avoiding the need for expensive global data structures.
The closest analogue among other well-known allocators is probably OpenBSD's omalloc.
Base allocation granularity and alignment is 16 bytes. Large
allocations are made individually by mmap, but they also have
out-of-band metadata records treating them as special one-member
groups, allowing realloc
and free
to validate them. Smaller
allocations come from groups of one of 48 size classes, spaced
linearly up to 128 (the first 8 classes), then roughly geometrically
with four steps per doubling, but adjusted to divide powers of two
with minimal remainder (waste).