Function exec_new_vmspace

freebsd/kern/kern_exec.c:1035–1149

* Destroy old address space, and allocate a new stack. * The new stack is only sgrowsiz large because it is grown * automatically on a page fault. */

 *	automatically on a page fault.
 */
int
exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv)
{
	int error;
	struct proc *p = imgp->proc;
	struct vmspace *vmspace = p->p_vmspace;
	struct thread *td = curthread;
	vm_object_t obj;
	struct rlimit rlim_stack;
	vm_offset_t sv_minuser, stack_addr;
	vm_map_t map;
	vm_prot_t stack_prot;
	u_long ssiz;

	imgp->vmspace_destroyed = 1;
	imgp->sysent = sv;

	sigfastblock_clear(td);
	umtx_exec(p);
	itimers_exec(p);
	if (sv->sv_onexec != NULL)
		sv->sv_onexec(p, imgp);

	EVENTHANDLER_DIRECT_INVOKE(process_exec, p, imgp);

	/*
	 * Blow away entire process VM, if address space not shared,
	 * otherwise, create a new VM space so that other threads are
	 * not disrupted
	 */
	map = &vmspace->vm_map;
	if (map_at_zero)
		sv_minuser = sv->sv_minuser;
	else
		sv_minuser = MAX(sv->sv_minuser, PAGE_SIZE);
	if (refcount_load(&vmspace->vm_refcnt) == 1 &&
	    vm_map_min(map) == sv_minuser &&
	    vm_map_max(map) == sv->sv_maxuser &&
	    cpu_exec_vmspace_reuse(p, map)) {
		shmexit(vmspace);
		pmap_remove_pages(vmspace_pmap(vmspace));
		vm_map_remove(map, vm_map_min(map), vm_map_max(map));
		/*
		 * An exec terminates mlockall(MCL_FUTURE).
		 * ASLR and W^X states must be re-evaluated.
		 */
		vm_map_lock(map);
		vm_map_modflags(map, 0, MAP_WIREFUTURE | MAP_ASLR |
		    MAP_ASLR_IGNSTART | MAP_WXORX);
		vm_map_unlock(map);
	} else {
		error = vmspace_exec(p, sv_minuser, sv->sv_maxuser);
		if (error)
			return (error);
		vmspace = p->p_vmspace;
		map = &vmspace->vm_map;
	}
	map->flags |= imgp->map_flags;