nx_thread.nx

nx_thread.nx -- clone(2)-based thread creation (CLONE_VM, CLONE_FS, CLONE_FILES, CLONE_SIGHAND, CLONE_THREAD). A "thread" on Linux is just a process that shares its parent's address space + file table + signal handlers. clone() with the right flags creates one. This module exposes a focused API on top of the raw syscall. Key constraint: the new thread starts at the function specified by `entry` with stack pointer set to `stack_top`. Caller must allocate the stack themselves (typically 64 KiB - 8 MiB). We don't pass the function via a function pointer (NishiLang has no first-class func type) -- caller passes the symbol address as i64 they obtained out-of-band. When NishiLang grows func types, the API takes a typed callback. Today the sim is single-threaded. Calling nx_thread_spawn against the host kernel will succeed (real threads are created) but the in-process simulator can't observe them. When SMP lands in nx_rv64_sim, the simulated CPU array maps onto host threads via this primitive. Pairs with nx_atom (atomic state across threads) + nx_mutex (futex-based blocking) + nx_proc (parent process abstraction).