This is a modified version of dlmalloc which delays the reuse of freed chunks and consolidate just-freed chunks before eventually returning them back to the free pool. This allocator is intended to be used in conjunction with CHERI to perform capability revocation.

Simply type make and link the final shared library "libdlmalloc_nonreuse.so". Do it like this:

CC=clang LD=ld.lld DEBUG=0 gmake

DEBUG=1 enables debugging assertions which slows down the allocator quite a bit. Only enable it in debugging.

The following compile-time #defines are the interesting bits to change or tweak. They live in the header file.

USE_LOCKS
USE_SPIN_LOCKS
USE_RECURSIVE_LOCKS
HAVE_MMAP
MAX_RELEASE_CHECK_RATE
FREEBUF_MODE
DEFAULT_FREEBUF_PERCENT
DEFAULT_SWEEP_SIZE
SWEEP_STATS
MALLOC_UTRACE

USE_LOCKS should be 1 for thread safety.

USE_SPIN_LOCKS is 0 to use pthreads, but pthreads on many platforms depend on malloc, so define it to 1 to use simple spin locks with C11 atomics.

USE_RECURSIVE_LOCKS should just be 0.

MAX_RELEASE_RATE indicates how many frees there are before traversing all segments to release unused ones. The default value is reasonable enough.

FREEBUF_MODE enables the delaying of freed chunks, putting them inside a free-buffer pool for consolidation and revocation before returning them to free lists. Defining it to 0 turns it into just the original dlmalloc.

DEFAULT_FREEBUF_PERCENT is the ratio of the size of the free-buffer pool to that of the normal heap, default being 25%.

DEFAULT_SWEEP_SIZE is for CHERI revocation, indicating how many chunks you want to sweep per sweeping pass.

SWEEP_STATS registers the printing of statistics via atexit(). On some platforms it has to be 0 because atexit() may depend on malloc.

MALLOC_UTRACE inject utrace entries for tracing. Define it to enable it. To collect traces, run the application with ktrace -tu cmd args... which generates a ktrace.out. Process it with kdump -tu > trace.log to parse the binary format into human readable entries.