Change BKPT and UDF encodings on ARM.

src/trusted/validator_arm/validator.cc

 /*
  * 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 <inttypes.h>
 
 #include "native_client/src/trusted/service_runtime/nacl_config.h"
 #include "native_client/src/trusted/validator_arm/model.h"
@@ skipping 657 matching lines @@
   return construction_failed_;
 }
 
 bool SfiValidator::validate_fallthrough(const CodeSegment& segment,
                                         ProblemSink* out,
                                         AddressSet* branches,
                                         AddressSet* critical) {
   bool complete_success = true;
 
   nacl_arm_dec::Forbidden initial_decoder;
-  // Initialize the previous instruction to a scary BKPT, so patterns all fail.
+  // Initialize the previous instruction so it always fails validation.
   DecodedInstruction pred(
       0,  // Virtual address 0, which will be in a different bundle;
-      Instruction(nacl_arm_dec::kLiteralPoolHeadInstruction),
+      Instruction(nacl_arm_dec::kFailValidation),
       initial_decoder);  // and ensure that it decodes as Forbidden.
 
   for (uint32_t va = segment.begin_addr(); va < segment.end_addr(); va += 4) {
     DecodedInstruction inst(va, segment[va],
                             decode_state_.decode(segment[va]));
 
     if (inst.safety() != nacl_arm_dec::MAY_BE_SAFE) {
       out->ReportProblemSafety(va, inst.safety());
       if (!out->should_continue()) {
         return false;
@@ skipping 210 matching lines @@
                                        Instruction inst,
                                        const ClassDecoder& decoder)
     : vaddr_(vaddr),
       inst_(inst),
       decoder_(&decoder),
       safety_(decoder.safety(inst_)),
       defs_(decoder.defs(inst_))
 {}
 
 }  // namespace nacl_arm_val