Dynamic loading: Fill pages with halts only when they are needed

src/native_client/tests/dynamic_code_loading/dyncode_demand_alloc_test.c

+/*
+ * Copyright (c) 2011 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/nacl_syscalls.h>
+
+#include "native_client/tests/dynamic_code_loading/dynamic_segment.h"
+
+
+uint8_t halts[] =
+#if defined(__i386__) || defined(__x86_64__)
+  { 0xf4 }; /* HLT */
+#elif defined(__arm__)
+  { 0x76, 0x66, 0x26, 0xe1 }; /* 0xe1266676 - BKPT 0x6666 */
+#else
+# error "Unknown arch"
+#endif
+
+
+void load_into_page(uint8_t *dest) {
+  uint8_t buf[32];
+  int rc;
+  uint8_t *ptr;
+
+  /* Touch the page by loading some halt instructions into it. */
+  for (ptr = buf; ptr < buf + sizeof(buf); ptr += sizeof(halts)) {
+    memcpy(ptr, halts, sizeof(halts));
+  }
+  rc = nacl_dyncode_create(dest, buf, sizeof(buf));
+  assert(rc == 0);
+
+  /* Check that the whole page is correctly filled with halts. */
+  for (ptr = dest; ptr < dest + DYNAMIC_CODE_PAGE_SIZE; ptr += sizeof(halts)) {
+    if (memcmp(ptr, halts, sizeof(halts)) != 0) {
+      fprintf(stderr, "Mismatch at %p\n", ptr);
+      exit(1);
+    }
+  }
+}
+
+int main() {
+  uint8_t *dyncode = (uint8_t *) DYNAMIC_CODE_SEGMENT_START;
+  int value;
+
+  /* Sanity check: First check that two code pages can be written and
+     read, before we check that the page inbetween is unreadable. */
+  load_into_page(dyncode);
+  load_into_page(dyncode + DYNAMIC_CODE_PAGE_SIZE * 2);
+
+  printf("Attempting to read from unallocated dyncode page.  "
+         "This should fault...\n");
+  value = dyncode[DYNAMIC_CODE_PAGE_SIZE];
+  printf("Failed: Dynamic code page was readable and contained the "
+         "byte 0x%x.\n", value);
+  return 1;
+}