[MIPS] Leave room for frame header on stack for MIPS arch

src/trusted/service_runtime/posix/nacl_signal.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 <errno.h>
 #include <signal.h>
 #include <stddef.h>
 #include <string.h>
@@ skipping 205 matching lines @@
 
   if (natp->exception_stack == 0) {
     new_stack_ptr = regs->stack_ptr - NACL_STACK_RED_ZONE;
   } else {
     new_stack_ptr = natp->exception_stack;
   }
   /* Allocate space for the stack frame, and ensure its alignment. */
   new_stack_ptr -=
       sizeof(struct NaClExceptionFrame) - NACL_STACK_PAD_BELOW_ALIGN;
   new_stack_ptr = new_stack_ptr & ~NACL_STACK_ALIGN_MASK;
+  new_stack_ptr -= NACL_STACK_ARG_SIZE;
   new_stack_ptr -= NACL_STACK_PAD_BELOW_ALIGN;
   frame_addr = NaClUserToSysAddrRange(nap, new_stack_ptr,
                                       sizeof(struct NaClExceptionFrame));
   if (frame_addr == kNaClBadAddress) {
     /* We cannot write the stack frame. */
     return 0;
   }
   context_user_addr = new_stack_ptr + offsetof(struct NaClExceptionFrame,
                                                context);
 
@@ skipping 29 matching lines @@
   regs->lr = kReturnAddr;
   regs->r0 = context_user_addr;  /* Argument 1 */
   regs->prog_ctr = NaClUserToSys(nap, nap->exception_handler);
   regs->stack_ptr = NaClUserToSys(nap, new_stack_ptr);
 #elif NACL_ARCH(NACL_BUILD_ARCH) == NACL_mips
   frame->context.frame_ptr = regs->frame_ptr;
   regs->return_addr = kReturnAddr;
   regs->a0 = context_user_addr;
   regs->prog_ctr = NaClUserToSys(nap, nap->exception_handler);
   regs->stack_ptr = NaClUserToSys(nap, new_stack_ptr);
+  /*
+   * Per Linux/MIPS convention, PIC functions assume that t9 holds
+   * the function's address on entry.
+   */
+  regs->t9 = regs->prog_ctr;
 #else
 # error Unsupported architecture
 #endif
 
 #if NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86
   frame->return_addr = kReturnAddr;
   regs->flags &= ~NACL_X86_DIRECTION_FLAG;
 #endif
 
   return 1;
@@ skipping 175 matching lines @@
   unsigned int a;
 
   /* Remove all handlers */
   for (a = 0; a < NACL_ARRAY_SIZE(s_Signals); a++) {
     if (sigaction(s_Signals[a], &s_OldActions[a], NULL) != 0) {
       NaClLog(LOG_FATAL, "Failed to unregister handler for %d.\n\tERR:%s\n",
                           s_Signals[a], strerror(errno));
     }
   }
 }