Another point about glibc implementation of pthread_mutex_t (and IIRC even the glibc internal lll_t that implements simple mutex as few lines of assembly involv

Another point about glibc implementation of pthread_mutex_t (and IIRC even the glibc internal lll_t that implements simple mutex as few lines of assembly involving futex(2)) is that on 32/64b platforms the layout of the structure is compatible between 32b and 64b ABIs. The reason for that is that pthread_mutex can have pshared attribute and also it is used in implementation of higher-level posix-IPC primitives (sane implementation of all of which involves just placing the particular synchronization struct into shared memory and not somehow translating that into SysV-IPC).