Reserve 1GB at the base address of linux nacl_helper for Native Client.

chrome/nacl/nacl_helper_bootstrap_linux.c

+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Bootstraping the nacl_helper. This executable reserves the bottom 1G
+ * of the address space, then invokes nacl_helper_main. Note that,

[agl, 2011/08/16 16:44:39]

|nacl_helper_main| doesn't match up with the function below: |nacl_helper_init|.

[Brad Chen, 2011/08/16 18:05:16]

Done.

+ * as the text of this executable will eventually be overwritten by the
+ * native_client module, nacl_helper_init must not attempt to return.
+ */
+
+#include <stdlib.h>
+
+/* reserve 1GB of space */
+#define ONEGIG (1 << 30)
+char nacl_reserved_space[ONEGIG];

[agl, 2011/08/16 16:44:39]

You pass in linker arguments to make the text segment start at 64KB, but this
will live in the BSS. I assume it does what you want anyway?

[Brad Chen, 2011/08/16 18:05:16]

The kernel is quite inflexible about order of sections, so text comes first,
with RO-data and bss following immediately after modulo alignment. I have tested
this code with an appropriately-modified NaCl system and it works as intended.

On 2011/08/16 16:44:39, agl wrote:

+
+void nacl_helper_init(int argc, char *argv[],
+                      const char *nacl_reserved_space);
+
+int main(int argc, char *argv[]) {
+  nacl_helper_init(argc, argv, nacl_reserved_space);
+  abort();
+  return 0;  // convince the tools I'm sane.
+}