[MIPS] Restore the trusted stack in NaClSyscallSeg.

src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c

Index: src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
diff --git a/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c b/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
index 5aabbedc1ccbf070514acf6eedd55613eddeaf56..a5cb67dd6d7eb514788b3f7e43615ad6a433d3fa 100644
--- a/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
+++ b/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
@@ -26,7 +26,7 @@ NORETURN void NaClStartThreadInApp(struct NaClAppThread *natp,
                                    uint32_t             new_prog_ctr) {
   struct NaClThreadContext  *context;
 
-  natp->user.trusted_stack_ptr = (NaClGetStackPtr() & ~0xf) + 4;
+  natp->user.trusted_stack_ptr = NaClGetStackPtr() & ~NACL_STACK_ALIGN_MASK;
 
   context = &natp->user;
   context->new_prog_ctr = new_prog_ctr;
@@ -41,11 +41,6 @@ NORETURN void NaClStartThreadInApp(struct NaClAppThread *natp,
   context->sysret = context->stack_ptr;
 
   /*
-   * Just to be sure that app does not spoil gp
-   */
-  context->global_ptr = NaClGetGlobalPtr();
-
-  /*
    * context stored in $a0
    */
   NaClSwitch(context);