Don't modify memory access right when changing data in debug stub.

tests/gdb/gdb_test_guest.c

 /*
  * Copyright (c) 2012 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 <string.h>
 #include <alloca.h>
 
@@ skipping 36 matching lines @@
   int local_var = arg - 1;
   global_var = local_var;
   /*
    * Force using frame pointer for this function by calling alloca.
    * This allows to test skipping %esp modifying instructions when they
    * are located in the middle of the function.
    */
   global_ptr = alloca(arg);
 }
 
+int test_call_from_gdb(int arg) {
+  global_var = 2 * arg;
+  return 3 * arg;
+}
+
 int main(int argc, char **argv) {
   assert(argc >= 2);
 
   if (strcmp(argv[1], "break_inside_function") == 0) {
     test_two_line_function(1);
     return 0;
   }
   if (strcmp(argv[1], "stepi_after_break") == 0) {
     test_stepi_after_break();
     return 0;
   }
   if (strcmp(argv[1], "print_symbol") == 0) {
     return test_print_symbol();
   }
   if (strcmp(argv[1], "stack_trace") == 0) {
     nested_calls(1);
     return 0;
   }
   if (strcmp(argv[1], "step_from_func_start") == 0) {
     global_var = 0;
     test_step_from_function_start(2);
     return 0;
   }
+  if (strcmp(argv[1], "call_from_gdb") == 0) {
+    /* Call function so that it doesn't optimized away. */

[Mark Seaborn, 2012/08/31 16:40:13]

"doesn't get optimized".  However, this shouldn't be necessary:  it shouldn't
get optimised away because:
 1) we don't use link-time optimisation with gcc, and the object file for this
file must include test_call_from_gdb();
 2) we build with -O0.

But also this wouldn't be sufficient in the case of LTO (e.g. with PNaCl),
because the function could get inlined away.

I'm just saying.  You don't necessarily need to change this.

[halyavin, 2012/09/03 10:33:50]

Done.

+    return test_call_from_gdb(0);
+  }
   return 1;
 }