More tests for ASST3.2

Added 2 new sbrktests, one to test a huge sbrk with only touch a few pages (shouldn't crash),
and another to make sure pages are getting freed when the breakpoint moves down. Also, added
a stacktest that checks that 4M stacks are supported and pages are allocated on-demand.

userland/testbin/stacktest/Makefile

@@ -0,0 +1,11 @@
+# Makefile for huge
+
+TOP=../../..
+.include "$(TOP)/mk/os161.config.mk"
+
+PROG=stacktest
+SRCS=stacktest.c
+BINDIR=/testbin
+
+.include "$(TOP)/mk/os161.prog.mk"
+

userland/testbin/stacktest/stacktest.c

@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * stacktest.c
+ *
+ * Tests the VM system's stack by allocating a large array on the stack and
+ * accessing it in a sparse manner. In total, we allocate 4*200*4096 = 3.125M
+ * on the stack. However, we only touch 1/4 of it, meaning this test should
+ * run when with <=2M of memory if stack pages are allocated on demand.
+ *
+ * When the VM system assignment is done, your system should be able
+ * to run this successfully.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <err.h>
+#include <errno.h>
+#include <test161/test161.h>
+
+#define PageSize	4096
+#define NumPages	200
+#define Answer      4900
+
+static int
+stacktest1()
+{
+	int sparse[NumPages][PageSize];
+	int i, j;
+
+	for (i = 0; i < NumPages; i+=4) {
+		// This is a fresh stack frame, so it better be zeroed. Otherwise,
+		// the kernel is leaking information between processes.
+		for (j = 0; j < PageSize/4; j++) {
+			if (sparse[i][j] != 0) {
+				errx(1, "Your stack pages are leaking data!");
+			}
+		}
+		sparse[i][0] = i;
+	}
+
+	// We need to do something with the values so the compiler doesn't
+	// optimize this array away.
+	int total = 0;
+	for (i = 0; i < NumPages; i+=4) {
+		total += sparse[i][0];
+	}
+
+	return total;
+}
+
+int
+main(void)
+{
+	int total = stacktest1();
+	if (total != Answer) {
+		errx(1, "Expected %d got %d\n", Answer, total);
+	}
+
+	// Success is not crashing
+	success(TEST161_SUCCESS, SECRET, "/testbin/stacktest");
+	return 0;
+}