c6943acb3c
Some system libraries are using malloc_default_zone() and then using some of the malloc_zone_* API. Under normal conditions, those functions check the malloc_zone_t/malloc_introspection_t struct for the values that are allowed to be NULL, so that a NULL deref doesn't happen. As of OSX 10.12, malloc_default_zone() doesn't return the actual default zone anymore, but returns a fake, wrapper zone. The wrapper zone defines all the possible functions in the malloc_zone_t/malloc_introspection_t struct (almost), and calls the function from the registered default zone (jemalloc in our case) on its own. Without checking whether the pointers are NULL. This means that a system library that calls e.g. malloc_zone_batch_malloc(malloc_default_zone(), ...) ends up trying to call jemalloc_zone.batch_malloc, which is NULL, and crash follows. So as of OSX 10.12, the default zone is required to have all the functions available (really, the same as the wrapper zone), even if they do nothing. This is arguably a bug in libsystem_malloc in OSX 10.12, but jemalloc still needs to work in that case.
jemalloc is a general purpose malloc(3) implementation that emphasizes fragmentation avoidance and scalable concurrency support. jemalloc first came into use as the FreeBSD libc allocator in 2005, and since then it has found its way into numerous applications that rely on its predictable behavior. In 2010 jemalloc development efforts broadened to include developer support features such as heap profiling, Valgrind integration, and extensive monitoring/tuning hooks. Modern jemalloc releases continue to be integrated back into FreeBSD, and therefore versatility remains critical. Ongoing development efforts trend toward making jemalloc among the best allocators for a broad range of demanding applications, and eliminating/mitigating weaknesses that have practical repercussions for real world applications. The COPYING file contains copyright and licensing information. The INSTALL file contains information on how to configure, build, and install jemalloc. The ChangeLog file contains a brief summary of changes for each release. URL: http://jemalloc.net/