Add documentation for the dynamic code modifications.

src/trusted/validator_ragel/unreviewed/gen_dfa.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 <assert.h>
 #include <fcntl.h>
 #include <getopt.h>
 #include <libgen.h>
@@ skipping 2222 matching lines @@
            prefix_it != required_prefixes.end(); ++prefix_it) {
         auto &prefix = *prefix_it;
         if (prefix == "0xf3") {
           fprintf(out_file, " @not_repz_prefix");
           break;
         }
       }
       if (enabled(Actions::kInstructionName)) {
         fprintf(out_file, " @instruction_%s", c_identifier(name).c_str());
       } else if (opcode_in_imm) {
-        fprintf(out_file, " @opcode_in_imm");
+        fprintf(out_file, " @last_byte_is_not_immediate");
       } else if (has_flag("nacl-amd64-modifiable") &&
                  enabled(Actions::kParseOperands) &&
                  !enabled(Actions::kParseOperandPositions)) {
         fprintf(out_file, " @modifiable_instruction");
       }
       for (auto flag_it = flags.begin(); flag_it != flags.end(); ++flag_it) {
         auto &flag = *flag_it;
         if (!strncmp(flag.c_str(), "CPUFeature_", 11)) {
           fprintf(out_file, " @%s", flag.c_str());
         }
@@ skipping 172 matching lines @@
                     (operand.source != 'R') && (operand.source != 'U') &&
                     (operand.source != 'W')) || !memory_access)) {
                 fprintf(out_file, " @operand%zd_%s", operand_index,
                                                                   operand_size);
               }
             }
           }
           static std::map<char, const char*> operand_type {
             { '1', "one"                },
             { 'a', "rax"                },
-            { 'b', "ds_rbx"             },
             { 'c', "rcx"                },
             { 'd', "rdx"                },
             { 'i', "second_immediate"   },
             { 'o', "port_dx"            },
             { 't', "st"                 },
+            { 'x', "ds_rbx"             },
             { 'B', "from_vex"           },
             { 'H', "from_vex"           },
             { 'I', "immediate"          },
             { 'O', "absolute_disp"      },
             { 'X', "ds_rsi"             },
             { 'Y', "es_rdi"             }
           };
           auto it2 = operand_type.find(operand.source);
           if (it2 != operand_type.end()) {
             if (operand.enabled) {
@@ skipping 113 matching lines @@
           }
           fprintf(out_file, " %s", it->second);
         }
         if (operand->source == 'L') {
           if (operands.size() == 4) {
             if (ia32_mode) {
               fprintf(out_file, " b_0xxx_0000");
             } else {
               fprintf(out_file, " b_xxxx_0000");
             }
+            if (!enabled(Actions::kInstructionName))
+              fprintf(out_file, " @last_byte_is_not_immediate");
           }
           if (operand->enabled && enabled(Actions::kParseOperands)) {
             fprintf(out_file, " @operand%zd_from_is4", operand_index - 1);
           }
         }
         if (operand->source == 'O') {
           if (ia32_mode) {
             fprintf(out_file, " disp32");
           } else {
             fprintf(out_file, " disp64");
@@ skipping 209 matching lines @@
 
   fprintf(out_file, "\n  one_instruction =");
 
   print_one_instruction_definition();
 
   fprintf(out_file, ");\n"
 "}%%%%\n"
 "");
   return 0;
 }