malloc_readonly
if (((uintptr_t)&malloc_readonly & MALLOC_PAGEMASK) == 0) {
if (mprotect(&malloc_readonly, sizeof(malloc_readonly),
if (mimmutable(&malloc_readonly,
sizeof(malloc_readonly)))
struct malloc_readonly mopts;
} malloc_readonly __attribute__((aligned(MALLOC_PAGESIZE)))
#define mopts malloc_readonly.mopts