mameMalloc

Plain header only implementation of malloc/free over a fixed buffer.

#include "mameMalloc.h"

static uint8_t pool[ 8192 ];

mameMalloc_initialize( pool, sizeof pool, 3 );  /* 1 << 3 == 8 byte blocks */
void* p = malloc( 100 );
free( p );
mameMalloc_finalize();

malloc, free, calloc and realloc are thin wrappers over mameMalloc_alloc and mameMalloc_free. All four are replaced together on purpose: replacing only malloc and free leaves calloc served by the C library while its pointers reach this free, which crashes. Defining MAME_MALLOC_DISABLE_STD_INTERFACE leaves the global malloc alone and exposes only the prefixed pair, which is what the sanitised test build uses — AddressSanitizer replaces malloc itself and cannot share it.

Outside the window between mameMalloc_initialize and mameMalloc_finalize, mameMalloc_alloc returns NULL and mameMalloc_free does nothing. It has to: with the wrapper on, library constructors reach malloc before main and teardown code reaches free after mameMalloc_finalize, and asserting there cannot work because assert formats its message through malloc and free.

• The definitions are neither static nor inline; including the header from more than one translation unit fails to link.
• A single global pool. There is no way to create a second one.
• Returned pointers are aligned to the block size, which mameMalloc_initialize requires to be at least sizeof(void*). That is not max_align_t, so an over-aligned type still needs a wider block.
• Not thread safe and not reentrant, so it is not safe to call from an interrupt handler.
• Every allocation costs sizeof(mameMalloc_header) on top of the payload, rounded up to the block size.

make test   # both suites
make main   # the original smoke test

test_mameMalloc.c drives the core allocator under ASan and UBSan. Each pool is mapped with a PROT_NONE page flush against its last byte and another before it, so anything that leaves the pool faults immediately — the sanitizers cannot see inside an mmap the allocator carves up by hand.

test_mameMalloc_std.c covers the malloc/free wrapper. It replaces the global allocator, so it builds without sanitizers and relies on the guard pages.

MIT. See LICENSE.