Function vm_map_growstack

freebsd/vm/vm_map.c:4623–4854

* Attempts to grow a vm stack entry. Returns KERN_SUCCESS if we * successfully grow the stack. */

 * successfully grow the stack.
 */
static int
vm_map_growstack(vm_map_t map, vm_offset_t addr, vm_map_entry_t gap_entry)
{
	vm_map_entry_t stack_entry;
	struct proc *p;
	struct vmspace *vm;
	struct ucred *cred;
	vm_offset_t gap_end, gap_start, grow_start;
	vm_size_t grow_amount, guard, max_grow;
	rlim_t lmemlim, stacklim, vmemlim;
	int rv, rv1;
	bool gap_deleted, grow_down, is_procstack;
#ifdef notyet
	uint64_t limit;
#endif
#ifdef RACCT
	int error;
#endif

	p = curproc;
	vm = p->p_vmspace;

	/*
	 * Disallow stack growth when the access is performed by a
	 * debugger or AIO daemon.  The reason is that the wrong
	 * resource limits are applied.
	 */
	if (p != initproc && (map != &p->p_vmspace->vm_map ||
	    p->p_textvp == NULL))
		return (KERN_FAILURE);

	MPASS(!map->system_map);

	lmemlim = lim_cur(curthread, RLIMIT_MEMLOCK);
	stacklim = lim_cur(curthread, RLIMIT_STACK);
	vmemlim = lim_cur(curthread, RLIMIT_VMEM);
retry:
	/* If addr is not in a hole for a stack grow area, no need to grow. */
	if (gap_entry == NULL && !vm_map_lookup_entry(map, addr, &gap_entry))
		return (KERN_FAILURE);
	if ((gap_entry->eflags & MAP_ENTRY_GUARD) == 0)
		return (KERN_SUCCESS);
	if ((gap_entry->eflags & MAP_ENTRY_STACK_GAP_DN) != 0) {
		stack_entry = vm_map_entry_succ(gap_entry);
		if ((stack_entry->eflags & MAP_ENTRY_GROWS_DOWN) == 0 ||
		    stack_entry->start != gap_entry->end)
			return (KERN_FAILURE);
		grow_amount = round_page(stack_entry->start - addr);
		grow_down = true;
	} else if ((gap_entry->eflags & MAP_ENTRY_STACK_GAP_UP) != 0) {
		stack_entry = vm_map_entry_pred(gap_entry);
		if ((stack_entry->eflags & MAP_ENTRY_GROWS_UP) == 0 ||
		    stack_entry->end != gap_entry->start)
			return (KERN_FAILURE);
		grow_amount = round_page(addr + 1 - stack_entry->end);
		grow_down = false;
	} else {
		return (KERN_FAILURE);