[MIPS] Make $t8 point to the address of TLS pointers

src/trusted/service_runtime/arch/mips/nacl_syscall.S

 /*
  * 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 "native_client/src/trusted/service_runtime/arch/mips/sel_ldr_mips.h"
 #include "native_client/src/trusted/service_runtime/arch/mips/sel_rt.h"
 #include "native_client/src/trusted/service_runtime/nacl_config.h"
 
@@ skipping 68 matching lines @@
    * stack frame (o32 ABI), and place return address on top of that.
    */
   sw    $a3, 12($sp)
   sw    $a2,  8($sp)
   sw    $a1,  4($sp)
   sw    $a0,  0($sp)
   /* Save return address for returning to untrusted code. */
   sw    $ra, -4($sp)
   /* Save return address that indicates which trampoline was called. */
   sw    $t5, -8($sp)
+  add   $a0, $t8, -NACL_THREAD_CONTEXT_OFFSET_TLS_VALUE1
 
-  /* Load the __thread variable's offset into a3. */
-  lui   $a3, %tprel_hi(nacl_current_thread)
-  addiu $a3, $a3, %tprel_lo(nacl_current_thread)
+  lw    $t2, NACL_THREAD_CONTEXT_OFFSET_GUARD_TOKEN($a0)
+  la    $t3, nacl_guard_token
+  lw    $t3, 0($t3)
+  bne   $t2, $t3, NaClSyscallThreadCaptureFault
+  nop
 
-  /* Fetch the thread-local variable: set a0 = nacl_current_thread */
-  rdhwr $v1, $29
-  addu  $a3, $v1, $a3
-  lw    $a0, 0($a3)
-
-DEFINE_GLOBAL_HIDDEN_LOCATION(NaClSyscallThreadCaptureFault):
   sw $s0, NACL_THREAD_CONTEXT_OFFSET_S0($a0)
   sw $s1, NACL_THREAD_CONTEXT_OFFSET_S1($a0)
   sw $s2, NACL_THREAD_CONTEXT_OFFSET_S2($a0)
   sw $s3, NACL_THREAD_CONTEXT_OFFSET_S3($a0)
   sw $s4, NACL_THREAD_CONTEXT_OFFSET_S4($a0)
   sw $s5, NACL_THREAD_CONTEXT_OFFSET_S5($a0)
   sw $s6, NACL_THREAD_CONTEXT_OFFSET_S6($a0)
   sw $s7, NACL_THREAD_CONTEXT_OFFSET_S7($a0)
   sw $t8, NACL_THREAD_CONTEXT_OFFSET_T8($a0)
   sw $sp, NACL_THREAD_CONTEXT_OFFSET_STACK_PTR($a0)
@@ skipping 15 matching lines @@
   lw    $t9,%call16(NaClSwitch)($s0)
   jr    $t9
   move  $a0, $v0 /* delay slot */
 
   /* NOTREACHED */
 
   /*
    * If the thread returns, which must not happen, it will be halted
    * by the following instruction.
    */
-
+DEFINE_GLOBAL_HIDDEN_LOCATION(NaClSyscallThreadCaptureFault):
   .word NACL_HALT_WORD