Many small edits.

src/libthread/thread.c

@@ -169,6 +169,7 @@ _threadswitch(void)
 {
 	Proc *p;
 
+	needstack(0);
 	p = proc();
 //print("threadswtch %p\n", p);
 	contextswitch(&p->thread->context, &p->schedcontext);
@@ -324,6 +325,20 @@ threadsetstate(char *fmt, ...)
 	va_end(arg);
 }
 
+void
+needstack(int n)
+{
+	_Thread *t;
+
+	t = proc()->thread;
+
+	if((char*)&t <= (char*)t->stk
+	|| (char*)&t - (char*)t->stk < 256+n){
+		fprint(2, "thread stack overflow\n");
+		abort();
+	}
+}
+
 /*
  * locking
  */
@@ -499,11 +514,6 @@ threadmainstart(void *v)
 	threadmain(threadargc, threadargv);
 }
 
-void
-threadlinklibrary(void)
-{
-}
-
 int
 main(int argc, char **argv)
 {