[MIPS] Implementation of sel_ldr for MIPS architecture.

src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.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.
- */
+* 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.
+*/
 
 /*
  * NaCl Service Runtime, C-level context switch code.
  */
 
 #include "native_client/src/shared/platform/nacl_check.h"
-#include "native_client/src/trusted/service_runtime/sel_ldr.h"
-#include "native_client/src/trusted/service_runtime/arch/arm/sel_rt.h"
+#include "native_client/src/trusted/service_runtime/arch/mips/sel_rt.h"
 #include "native_client/src/trusted/service_runtime/nacl_app_thread.h"
 #include "native_client/src/trusted/service_runtime/nacl_globals.h"
 #include "native_client/src/trusted/service_runtime/nacl_switch_to_app.h"
+#include "native_client/src/trusted/service_runtime/sel_ldr.h"
 
 void NaClInitSwitchToApp(struct NaClApp *nap) {
-  /*
-   * We don't need anything here.  We might need it in future if e.g.
-   * we start letting untrusted code use NEON extensions.
-   */
+ /*
+  * We don't need anything here.
+  */
   UNREFERENCED_PARAMETER(nap);
 }
 
 NORETURN void NaClStartThreadInApp(struct NaClAppThread *natp,
                                    uint32_t             new_prog_ctr) {
   struct NaClApp  *nap;
   struct NaClThreadContext  *context;
 
-  natp->user.trusted_stack_ptr = NaClGetStackPtr() & ~0xf;
+  natp->user.trusted_stack_ptr = (NaClGetStackPtr() & ~0xf) + 4;
 
   nap = natp->nap;
   context = &natp->user;
   context->new_prog_ctr = new_prog_ctr;
 
   /*
    * At startup this is not the return value, but the first argument.
    * In the initial thread, it gets the pointer to the information
    * block on the stack.  Additional threads do not expect anything in
    * particular in the first argument register, so we don't bother to
    * conditionalize this.
    */
   context->sysret = context->stack_ptr;
 
+  /*
+   * Define load/store and jump masks before switching to app
+   */
+  context->t6 = NACL_CONTROL_FLOW_MASK;
+  context->t7 = NACL_DATA_FLOW_MASK;
+
+  /*
+   * Just to be sure that app does not spoil gp
+   */
+  context->global_ptr = NaClGetGlobalPtr();
+
+  /*
+   * context stored in $a0
+   */
   NaClSwitch(context);
 }
 
 /*
  * syscall return
  */
 NORETURN void NaClSwitchToApp(struct NaClAppThread *natp) {
   NaClSwitch(&natp->user);
 }