libthread: make page work on OS X

src/libthread/exec.c

@@ -62,6 +62,7 @@ _threadspawn(int fd[3], char *cmd, char *argv[])
 	int i, n, p[2], pid;
 	char exitstr[100];
 
+	notifyoff("sys: child");	/* do not let child note kill us */
 	if(pipe(p) < 0)
 		return -1;
 	if(fcntl(p[0], F_SETFD, 1) < 0 || fcntl(p[1], F_SETFD, 1) < 0){

src/libthread/thread.c

@@ -155,6 +155,10 @@ _threadcreate(Proc *p, void (*fn)(void*), void *arg, uint stack)
 {
 	_Thread *t;
 
+	/* defend against bad C libraries */
+	if(stack < (256<<10))
+		stack = 256<<10;
+	
 	t = threadalloc(fn, arg, stack);
 	t->proc = p;
 	addthreadinproc(p, t);