Add m-esr52 at 52.6.0

1 files changed, 1535 insertions, 0 deletions

diff --git a/js/src/jit/arm64/vixl/Debugger-vixl.cpp b/js/src/jit/arm64/vixl/Debugger-vixl.cpp
new file mode 100644
index 000000000..85097ed5a
--- /dev/null
+++ b/js/src/jit/arm64/vixl/Debugger-vixl.cpp
@@ -0,0 +1,1535 @@
+// Copyright 2014, ARM Limited
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//   * Redistributions of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//   * Redistributions in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//   * Neither the name of ARM Limited nor the names of its contributors may be
+//     used to endorse or promote products derived from this software without
+//     specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY ARM LIMITED AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL ARM LIMITED BE LIABLE FOR ANY DIRECT, INDIRECT,
+// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
+// OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+// EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "js-config.h"
+
+#ifdef JS_SIMULATOR_ARM64
+
+#include "jit/arm64/vixl/Debugger-vixl.h"
+
+#include "mozilla/Vector.h"
+
+#include "jsalloc.h"
+
+namespace vixl {
+
+// List of commands supported by the debugger.
+#define DEBUG_COMMAND_LIST(C)  \
+C(HelpCommand)                 \
+C(ContinueCommand)             \
+C(StepCommand)                 \
+C(DisasmCommand)               \
+C(PrintCommand)                \
+C(ExamineCommand)
+
+// Debugger command lines are broken up in token of different type to make
+// processing easier later on.
+class Token {
+ public:
+  virtual ~Token() {}
+
+  // Token type.
+  virtual bool IsRegister() const { return false; }
+  virtual bool IsFPRegister() const { return false; }
+  virtual bool IsIdentifier() const { return false; }
+  virtual bool IsAddress() const { return false; }
+  virtual bool IsInteger() const { return false; }
+  virtual bool IsFormat() const { return false; }
+  virtual bool IsUnknown() const { return false; }
+  // Token properties.
+  virtual bool CanAddressMemory() const { return false; }
+  virtual uint8_t* ToAddress(Debugger* debugger) const = 0;
+  virtual void Print(FILE* out = stdout) const = 0;
+
+  static Token* Tokenize(const char* arg);
+};
+
+typedef mozilla::Vector<Token*, 0, js::SystemAllocPolicy> TokenVector;
+
+// Tokens often hold one value.
+template<typename T> class ValueToken : public Token {
+ public:
+  explicit ValueToken(T value) : value_(value) {}
+  ValueToken() {}
+
+  T value() const { return value_; }
+
+  virtual uint8_t* ToAddress(Debugger* debugger) const {
+    USE(debugger);
+    VIXL_ABORT();
+  }
+
+ protected:
+  T value_;
+};
+
+// Integer registers (X or W) and their aliases.
+// Format: wn or xn with 0 <= n < 32 or a name in the aliases list.
+class RegisterToken : public ValueToken<const Register> {
+ public:
+  explicit RegisterToken(const Register reg)
+      : ValueToken<const Register>(reg) {}
+
+  virtual bool IsRegister() const { return true; }
+  virtual bool CanAddressMemory() const { return value().Is64Bits(); }
+  virtual uint8_t* ToAddress(Debugger* debugger) const;
+  virtual void Print(FILE* out = stdout) const ;
+  const char* Name() const;
+
+  static Token* Tokenize(const char* arg);
+  static RegisterToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsRegister());
+    return reinterpret_cast<RegisterToken*>(tok);
+  }
+
+ private:
+  static const int kMaxAliasNumber = 4;
+  static const char* kXAliases[kNumberOfRegisters][kMaxAliasNumber];
+  static const char* kWAliases[kNumberOfRegisters][kMaxAliasNumber];
+};
+
+// Floating point registers (D or S).
+// Format: sn or dn with 0 <= n < 32.
+class FPRegisterToken : public ValueToken<const FPRegister> {
+ public:
+  explicit FPRegisterToken(const FPRegister fpreg)
+      : ValueToken<const FPRegister>(fpreg) {}
+
+  virtual bool IsFPRegister() const { return true; }
+  virtual void Print(FILE* out = stdout) const ;
+
+  static Token* Tokenize(const char* arg);
+  static FPRegisterToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsFPRegister());
+    return reinterpret_cast<FPRegisterToken*>(tok);
+  }
+};
+
+
+// Non-register identifiers.
+// Format: Alphanumeric string starting with a letter.
+class IdentifierToken : public ValueToken<char*> {
+ public:
+  explicit IdentifierToken(const char* name) {
+    size_t size = strlen(name) + 1;
+    value_ = (char*)js_malloc(size);
+    strncpy(value_, name, size);
+  }
+  virtual ~IdentifierToken() { js_free(value_); }
+
+  virtual bool IsIdentifier() const { return true; }
+  virtual bool CanAddressMemory() const { return strcmp(value(), "pc") == 0; }
+  virtual uint8_t* ToAddress(Debugger* debugger) const;
+  virtual void Print(FILE* out = stdout) const;
+
+  static Token* Tokenize(const char* arg);
+  static IdentifierToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsIdentifier());
+    return reinterpret_cast<IdentifierToken*>(tok);
+  }
+};
+
+// 64-bit address literal.
+// Format: 0x... with up to 16 hexadecimal digits.
+class AddressToken : public ValueToken<uint8_t*> {
+ public:
+  explicit AddressToken(uint8_t* address) : ValueToken<uint8_t*>(address) {}
+
+  virtual bool IsAddress() const { return true; }
+  virtual bool CanAddressMemory() const { return true; }
+  virtual uint8_t* ToAddress(Debugger* debugger) const;
+  virtual void Print(FILE* out = stdout) const ;
+
+  static Token* Tokenize(const char* arg);
+  static AddressToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsAddress());
+    return reinterpret_cast<AddressToken*>(tok);
+  }
+};
+
+
+// 64-bit decimal integer literal.
+// Format: n.
+class IntegerToken : public ValueToken<int64_t> {
+ public:
+  explicit IntegerToken(int64_t value) : ValueToken<int64_t>(value) {}
+
+  virtual bool IsInteger() const { return true; }
+  virtual void Print(FILE* out = stdout) const;
+
+  static Token* Tokenize(const char* arg);
+  static IntegerToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsInteger());
+    return reinterpret_cast<IntegerToken*>(tok);
+  }
+};
+
+// Literal describing how to print a chunk of data (up to 64 bits).
+// Format: .ln
+// where l (letter) is one of
+//  * x: hexadecimal
+//  * s: signed integer
+//  * u: unsigned integer
+//  * f: floating point
+//  * i: instruction
+// and n (size) is one of 8, 16, 32 and 64. n should be omitted for
+// instructions.
+class FormatToken : public Token {
+ public:
+  FormatToken() {}
+
+  virtual bool IsFormat() const { return true; }
+  virtual int SizeOf() const = 0;
+  virtual char type_code() const = 0;
+  virtual void PrintData(void* data, FILE* out = stdout) const = 0;
+  virtual void Print(FILE* out = stdout) const = 0;
+
+  virtual uint8_t* ToAddress(Debugger* debugger) const {
+    USE(debugger);
+    VIXL_ABORT();
+  }
+
+  static Token* Tokenize(const char* arg);
+  static FormatToken* Cast(Token* tok) {
+    VIXL_ASSERT(tok->IsFormat());
+    return reinterpret_cast<FormatToken*>(tok);
+  }
+};
+
+
+template<typename T> class Format : public FormatToken {
+ public:
+  Format(const char* fmt, char type_code) : fmt_(fmt), type_code_(type_code) {}
+
+  virtual int SizeOf() const { return sizeof(T); }
+  virtual char type_code() const { return type_code_; }
+  virtual void PrintData(void* data, FILE* out = stdout) const {
+    T value;
+    memcpy(&value, data, sizeof(value));
+    fprintf(out, fmt_, value);
+  }
+  virtual void Print(FILE* out = stdout) const;
+
+ private:
+  const char* fmt_;
+  char type_code_;
+};
+
+// Tokens which don't fit any of the above.
+class UnknownToken : public Token {
+ public:
+  explicit UnknownToken(const char* arg) {
+    size_t size = strlen(arg) + 1;
+    unknown_ = (char*)js_malloc(size);
+    strncpy(unknown_, arg, size);
+  }
+  virtual ~UnknownToken() { js_free(unknown_); }
+  virtual uint8_t* ToAddress(Debugger* debugger) const {
+    USE(debugger);
+    VIXL_ABORT();
+  }
+
+  virtual bool IsUnknown() const { return true; }
+  virtual void Print(FILE* out = stdout) const;
+
+ private:
+  char* unknown_;
+};
+
+
+// All debugger commands must subclass DebugCommand and implement Run, Print
+// and Build. Commands must also define kHelp and kAliases.
+class DebugCommand {
+ public:
+  explicit DebugCommand(Token* name) : name_(IdentifierToken::Cast(name)) {}
+  DebugCommand() : name_(NULL) {}
+  virtual ~DebugCommand() { js_delete(name_); }
+
+  const char* name() { return name_->value(); }
+  // Run the command on the given debugger. The command returns true if
+  // execution should move to the next instruction.
+  virtual bool Run(Debugger * debugger) = 0;
+  virtual void Print(FILE* out = stdout);
+
+  static bool Match(const char* name, const char** aliases);
+  static DebugCommand* Parse(char* line);
+  static void PrintHelp(const char** aliases,
+                        const char* args,
+                        const char* help);
+
+ private:
+  IdentifierToken* name_;
+};
+
+// For all commands below see their respective kHelp and kAliases in
+// debugger-a64.cc
+class HelpCommand : public DebugCommand {
+ public:
+  explicit HelpCommand(Token* name) : DebugCommand(name) {}
+
+  virtual bool Run(Debugger* debugger);
+
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+};
+
+
+class ContinueCommand : public DebugCommand {
+ public:
+  explicit ContinueCommand(Token* name) : DebugCommand(name) {}
+
+  virtual bool Run(Debugger* debugger);
+
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+};
+
+
+class StepCommand : public DebugCommand {
+ public:
+  StepCommand(Token* name, IntegerToken* count)
+      : DebugCommand(name), count_(count) {}
+  virtual ~StepCommand() { js_delete(count_); }
+
+  int64_t count() { return count_->value(); }
+  virtual bool Run(Debugger* debugger);
+  virtual void Print(FILE* out = stdout);
+
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+
+ private:
+  IntegerToken* count_;
+};
+
+class DisasmCommand : public DebugCommand {
+ public:
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+};
+
+
+class PrintCommand : public DebugCommand {
+ public:
+  PrintCommand(Token* name, Token* target, FormatToken* format)
+      : DebugCommand(name), target_(target), format_(format) {}
+  virtual ~PrintCommand() {
+    js_delete(target_);
+    js_delete(format_);
+  }
+
+  Token* target() { return target_; }
+  FormatToken* format() { return format_; }
+  virtual bool Run(Debugger* debugger);
+  virtual void Print(FILE* out = stdout);
+
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+
+ private:
+  Token* target_;
+  FormatToken* format_;
+};
+
+class ExamineCommand : public DebugCommand {
+ public:
+  ExamineCommand(Token* name,
+                 Token* target,
+                 FormatToken* format,
+                 IntegerToken* count)
+      : DebugCommand(name), target_(target), format_(format), count_(count) {}
+  virtual ~ExamineCommand() {
+    js_delete(target_);
+    js_delete(format_);
+    js_delete(count_);
+  }
+
+  Token* target() { return target_; }
+  FormatToken* format() { return format_; }
+  IntegerToken* count() { return count_; }
+  virtual bool Run(Debugger* debugger);
+  virtual void Print(FILE* out = stdout);
+
+  static DebugCommand* Build(TokenVector&& args);
+
+  static const char* kHelp;
+  static const char* kAliases[];
+  static const char* kArguments;
+
+ private:
+  Token* target_;
+  FormatToken* format_;
+  IntegerToken* count_;
+};
+
+// Commands which name does not match any of the known commnand.
+class UnknownCommand : public DebugCommand {
+ public:
+  explicit UnknownCommand(TokenVector&& args) : args_(Move(args)) {}
+  virtual ~UnknownCommand();
+
+  virtual bool Run(Debugger* debugger);
+
+ private:
+  TokenVector args_;
+};
+
+// Commands which name match a known command but the syntax is invalid.
+class InvalidCommand : public DebugCommand {
+ public:
+  InvalidCommand(TokenVector&& args, int index, const char* cause)
+      : args_(Move(args)), index_(index), cause_(cause) {}
+  virtual ~InvalidCommand();
+
+  virtual bool Run(Debugger* debugger);
+
+ private:
+  TokenVector args_;
+  int index_;
+  const char* cause_;
+};
+
+const char* HelpCommand::kAliases[] = { "help", NULL };
+const char* HelpCommand::kArguments = NULL;
+const char* HelpCommand::kHelp = "  Print this help.";
+
+const char* ContinueCommand::kAliases[] = { "continue", "c", NULL };
+const char* ContinueCommand::kArguments = NULL;
+const char* ContinueCommand::kHelp = "  Resume execution.";
+
+const char* StepCommand::kAliases[] = { "stepi", "si", NULL };
+const char* StepCommand::kArguments = "[n = 1]";
+const char* StepCommand::kHelp = "  Execute n next instruction(s).";
+
+const char* DisasmCommand::kAliases[] = { "disasm", "di", NULL };
+const char* DisasmCommand::kArguments = "[n = 10]";
+const char* DisasmCommand::kHelp =
+  "  Disassemble n instruction(s) at pc.\n"
+  "  This command is equivalent to x pc.i [n = 10]."
+;
+
+const char* PrintCommand::kAliases[] = { "print", "p", NULL };
+const char* PrintCommand::kArguments =  "<entity>[.format]";
+const char* PrintCommand::kHelp =
+  "  Print the given entity according to the given format.\n"
+  "  The format parameter only affects individual registers; it is ignored\n"
+  "  for other entities.\n"
+  "  <entity> can be one of the following:\n"
+  "   * A register name (such as x0, s1, ...).\n"
+  "   * 'regs', to print all integer (W and X) registers.\n"
+  "   * 'fpregs' to print all floating-point (S and D) registers.\n"
+  "   * 'sysregs' to print all system registers (including NZCV).\n"
+  "   * 'pc' to print the current program counter.\n"
+;
+
+const char* ExamineCommand::kAliases[] = { "m", "mem", "x", NULL };
+const char* ExamineCommand::kArguments = "<addr>[.format] [n = 10]";
+const char* ExamineCommand::kHelp =
+  "  Examine memory. Print n items of memory at address <addr> according to\n"
+  "  the given [.format].\n"
+  "  Addr can be an immediate address, a register name or pc.\n"
+  "  Format is made of a type letter: 'x' (hexadecimal), 's' (signed), 'u'\n"
+  "  (unsigned), 'f' (floating point), i (instruction) and a size in bits\n"
+  "  when appropriate (8, 16, 32, 64)\n"
+  "  E.g 'x sp.x64' will print 10 64-bit words from the stack in\n"
+  "  hexadecimal format."
+;
+
+const char* RegisterToken::kXAliases[kNumberOfRegisters][kMaxAliasNumber] = {
+  { "x0", NULL },
+  { "x1", NULL },
+  { "x2", NULL },
+  { "x3", NULL },
+  { "x4", NULL },
+  { "x5", NULL },
+  { "x6", NULL },
+  { "x7", NULL },
+  { "x8", NULL },
+  { "x9", NULL },
+  { "x10", NULL },
+  { "x11", NULL },
+  { "x12", NULL },
+  { "x13", NULL },
+  { "x14", NULL },
+  { "x15", NULL },
+  { "ip0", "x16", NULL },
+  { "ip1", "x17", NULL },
+  { "x18", "pr", NULL },
+  { "x19", NULL },
+  { "x20", NULL },
+  { "x21", NULL },
+  { "x22", NULL },
+  { "x23", NULL },
+  { "x24", NULL },
+  { "x25", NULL },
+  { "x26", NULL },
+  { "x27", NULL },
+  { "x28", NULL },
+  { "fp", "x29", NULL },
+  { "lr", "x30", NULL },
+  { "sp", NULL}
+};
+
+const char* RegisterToken::kWAliases[kNumberOfRegisters][kMaxAliasNumber] = {
+  { "w0", NULL },
+  { "w1", NULL },
+  { "w2", NULL },
+  { "w3", NULL },
+  { "w4", NULL },
+  { "w5", NULL },
+  { "w6", NULL },
+  { "w7", NULL },
+  { "w8", NULL },
+  { "w9", NULL },
+  { "w10", NULL },
+  { "w11", NULL },
+  { "w12", NULL },
+  { "w13", NULL },
+  { "w14", NULL },
+  { "w15", NULL },
+  { "w16", NULL },
+  { "w17", NULL },
+  { "w18", NULL },
+  { "w19", NULL },
+  { "w20", NULL },
+  { "w21", NULL },
+  { "w22", NULL },
+  { "w23", NULL },
+  { "w24", NULL },
+  { "w25", NULL },
+  { "w26", NULL },
+  { "w27", NULL },
+  { "w28", NULL },
+  { "w29", NULL },
+  { "w30", NULL },
+  { "wsp", NULL }
+};
+
+
+Debugger::Debugger(Decoder* decoder, FILE* stream)
+    : Simulator(decoder, stream),
+      debug_parameters_(DBG_INACTIVE),
+      pending_request_(false),
+      steps_(0),
+      last_command_(NULL) {
+  disasm_ = js_new<PrintDisassembler>(stdout);
+  printer_ = js_new<Decoder>();
+  printer_->AppendVisitor(disasm_);
+}
+
+
+Debugger::~Debugger() {
+  js_delete(disasm_);
+  js_delete(printer_);
+}
+
+
+void Debugger::Run() {
+  pc_modified_ = false;
+  while (pc_ != kEndOfSimAddress) {
+    if (pending_request()) RunDebuggerShell();
+    ExecuteInstruction();
+    LogAllWrittenRegisters();
+  }
+}
+
+
+void Debugger::PrintInstructions(const void* address, int64_t count) {
+  if (count == 0) {
+    return;
+  }
+
+  const Instruction* from = Instruction::CastConst(address);
+  if (count < 0) {
+    count = -count;
+    from -= (count - 1) * kInstructionSize;
+  }
+  const Instruction* to = from + count * kInstructionSize;
+
+  for (const Instruction* current = from;
+       current < to;
+       current = current->NextInstruction()) {
+    printer_->Decode(current);
+  }
+}
+
+
+void Debugger::PrintMemory(const uint8_t* address,
+                           const FormatToken* format,
+                           int64_t count) {
+  if (count == 0) {
+    return;
+  }
+
+  const uint8_t* from = address;
+  int size = format->SizeOf();
+  if (count < 0) {
+    count = -count;
+    from -= (count - 1) * size;
+  }
+  const uint8_t* to = from + count * size;
+
+  for (const uint8_t* current = from; current < to; current += size) {
+    if (((current - from) % 8) == 0) {
+      printf("\n%p: ", current);
+    }
+
+    uint64_t data = Memory::Read<uint64_t>(current);
+    format->PrintData(&data);
+    printf(" ");
+  }
+  printf("\n\n");
+}
+
+
+void Debugger::PrintRegister(const Register& target_reg,
+                             const char* name,
+                             const FormatToken* format) {
+  const uint64_t reg_size = target_reg.size();
+  const uint64_t format_size = format->SizeOf() * 8;
+  const uint64_t count = reg_size / format_size;
+  const uint64_t mask = 0xffffffffffffffff >> (64 - format_size);
+  const uint64_t reg_value = reg<uint64_t>(target_reg.code(),
+                                           Reg31IsStackPointer);
+  VIXL_ASSERT(count > 0);
+
+  printf("%s = ", name);
+  for (uint64_t i = 1; i <= count; i++) {
+    uint64_t data = reg_value >> (reg_size - (i * format_size));
+    data &= mask;
+    format->PrintData(&data);
+    printf(" ");
+  }
+  printf("\n");
+}
+
+
+// TODO(all): fix this for vector registers.
+void Debugger::PrintFPRegister(const FPRegister& target_fpreg,
+                               const FormatToken* format) {
+  const unsigned fpreg_size = target_fpreg.size();
+  const uint64_t format_size = format->SizeOf() * 8;
+  const uint64_t count = fpreg_size / format_size;
+  const uint64_t mask = 0xffffffffffffffff >> (64 - format_size);
+  const uint64_t fpreg_value = vreg<uint64_t>(fpreg_size, target_fpreg.code());
+  VIXL_ASSERT(count > 0);
+
+  if (target_fpreg.Is32Bits()) {
+    printf("s%u = ", target_fpreg.code());
+  } else {
+    printf("d%u = ", target_fpreg.code());
+  }
+  for (uint64_t i = 1; i <= count; i++) {
+    uint64_t data = fpreg_value >> (fpreg_size - (i * format_size));
+    data &= mask;
+    format->PrintData(&data);
+    printf(" ");
+  }
+  printf("\n");
+}
+
+
+void Debugger::VisitException(const Instruction* instr) {
+  switch (instr->Mask(ExceptionMask)) {
+    case BRK:
+      DoBreakpoint(instr);
+      return;
+    case HLT:
+      VIXL_FALLTHROUGH();
+    default: Simulator::VisitException(instr);
+  }
+}
+
+
+// Read a command. A command will be at most kMaxDebugShellLine char long and
+// ends with '\n\0'.
+// TODO: Should this be a utility function?
+char* Debugger::ReadCommandLine(const char* prompt, char* buffer, int length) {
+  int fgets_calls = 0;
+  char* end = NULL;
+
+  printf("%s", prompt);
+  fflush(stdout);
+
+  do {
+    if (fgets(buffer, length, stdin) == NULL) {
+      printf(" ** Error while reading command. **\n");
+      return NULL;
+    }
+
+    fgets_calls++;
+    end = strchr(buffer, '\n');
+  } while (end == NULL);
+
+  if (fgets_calls != 1) {
+    printf(" ** Command too long. **\n");
+    return NULL;
+  }
+
+  // Remove the newline from the end of the command.
+  VIXL_ASSERT(end[1] == '\0');
+  VIXL_ASSERT((end - buffer) < (length - 1));
+  end[0] = '\0';
+
+  return buffer;
+}
+
+
+void Debugger::RunDebuggerShell() {
+  if (IsDebuggerRunning()) {
+    if (steps_ > 0) {
+      // Finish stepping first.
+      --steps_;
+      return;
+    }
+
+    printf("Next: ");
+    PrintInstructions(pc());
+    bool done = false;
+    while (!done) {
+      char buffer[kMaxDebugShellLine];
+      char* line = ReadCommandLine("vixl> ", buffer, kMaxDebugShellLine);
+
+      if (line == NULL) continue;  // An error occurred.
+
+      DebugCommand* command = DebugCommand::Parse(line);
+      if (command != NULL) {
+        last_command_ = command;
+      }
+
+      if (last_command_ != NULL) {
+        done = last_command_->Run(this);
+      } else {
+        printf("No previous command to run!\n");
+      }
+    }
+
+    if ((debug_parameters_ & DBG_BREAK) != 0) {
+      // The break request has now been handled, move to next instruction.
+      debug_parameters_ &= ~DBG_BREAK;
+      increment_pc();
+    }
+  }
+}
+
+
+void Debugger::DoBreakpoint(const Instruction* instr) {
+  VIXL_ASSERT(instr->Mask(ExceptionMask) == BRK);
+
+  printf("Hit breakpoint at pc=%p.\n", reinterpret_cast<const void*>(instr));
+  set_debug_parameters(debug_parameters() | DBG_BREAK | DBG_ACTIVE);
+  // Make the shell point to the brk instruction.
+  set_pc(instr);
+}
+
+
+static bool StringToUInt64(uint64_t* value, const char* line, int base = 10) {
+  char* endptr = NULL;
+  errno = 0;  // Reset errors.
+  uint64_t parsed = strtoul(line, &endptr, base);
+
+  if (errno == ERANGE) {
+    // Overflow.
+    return false;
+  }
+
+  if (endptr == line) {
+    // No digits were parsed.
+    return false;
+  }
+
+  if (*endptr != '\0') {
+    // Non-digit characters present at the end.
+    return false;
+  }
+
+  *value = parsed;
+  return true;
+}
+
+
+static bool StringToInt64(int64_t* value, const char* line, int base = 10) {
+  char* endptr = NULL;
+  errno = 0;  // Reset errors.
+  int64_t parsed = strtol(line, &endptr, base);
+
+  if (errno == ERANGE) {
+    // Overflow, undeflow.
+    return false;
+  }
+
+  if (endptr == line) {
+    // No digits were parsed.
+    return false;
+  }
+
+  if (*endptr != '\0') {
+    // Non-digit characters present at the end.
+    return false;
+  }
+
+  *value = parsed;
+  return true;
+}
+
+
+Token* Token::Tokenize(const char* arg) {
+  if ((arg == NULL) || (*arg == '\0')) {
+    return NULL;
+  }
+
+  // The order is important. For example Identifier::Tokenize would consider
+  // any register to be a valid identifier.
+
+  Token* token = RegisterToken::Tokenize(arg);
+  if (token != NULL) {
+    return token;
+  }
+
+  token = FPRegisterToken::Tokenize(arg);
+  if (token != NULL) {
+    return token;
+  }
+
+  token = IdentifierToken::Tokenize(arg);
+  if (token != NULL) {
+    return token;
+  }
+
+  token = AddressToken::Tokenize(arg);
+  if (token != NULL) {
+    return token;
+  }
+
+  token = IntegerToken::Tokenize(arg);
+  if (token != NULL) {
+    return token;
+  }
+
+  return js_new<UnknownToken>(arg);
+}
+
+
+uint8_t* RegisterToken::ToAddress(Debugger* debugger) const {
+  VIXL_ASSERT(CanAddressMemory());
+  uint64_t reg_value = debugger->xreg(value().code(), Reg31IsStackPointer);
+  uint8_t* address = NULL;
+  memcpy(&address, &reg_value, sizeof(address));
+  return address;
+}
+
+
+void RegisterToken::Print(FILE* out) const {
+  VIXL_ASSERT(value().IsValid());
+  fprintf(out, "[Register %s]", Name());
+}
+
+
+const char* RegisterToken::Name() const {
+  if (value().Is32Bits()) {
+    return kWAliases[value().code()][0];
+  } else {
+    return kXAliases[value().code()][0];
+  }
+}
+
+
+Token* RegisterToken::Tokenize(const char* arg) {
+  for (unsigned i = 0; i < kNumberOfRegisters; i++) {
+    // Is it a X register or alias?
+    for (const char** current = kXAliases[i]; *current != NULL; current++) {
+      if (strcmp(arg, *current) == 0) {
+        return js_new<RegisterToken>(Register::XRegFromCode(i));
+      }
+    }
+
+    // Is it a W register or alias?
+    for (const char** current = kWAliases[i]; *current != NULL; current++) {
+      if (strcmp(arg, *current) == 0) {
+        return js_new<RegisterToken>(Register::WRegFromCode(i));
+      }
+    }
+  }
+
+  return NULL;
+}
+
+
+void FPRegisterToken::Print(FILE* out) const {
+  VIXL_ASSERT(value().IsValid());
+  char prefix = value().Is32Bits() ? 's' : 'd';
+  fprintf(out, "[FPRegister %c%" PRIu32 "]", prefix, value().code());
+}
+
+
+Token* FPRegisterToken::Tokenize(const char* arg) {
+  if (strlen(arg) < 2) {
+    return NULL;
+  }
+
+  switch (*arg) {
+    case 's':
+    case 'd':
+      const char* cursor = arg + 1;
+      uint64_t code = 0;
+      if (!StringToUInt64(&code, cursor)) {
+        return NULL;
+      }
+
+      if (code > kNumberOfFPRegisters) {
+        return NULL;
+      }
+
+      VRegister fpreg = NoVReg;
+      switch (*arg) {
+        case 's':
+          fpreg = VRegister::SRegFromCode(static_cast<unsigned>(code));
+          break;
+        case 'd':
+          fpreg = VRegister::DRegFromCode(static_cast<unsigned>(code));
+          break;
+        default: VIXL_UNREACHABLE();
+      }
+
+      return js_new<FPRegisterToken>(fpreg);
+  }
+
+  return NULL;
+}
+
+
+uint8_t* IdentifierToken::ToAddress(Debugger* debugger) const {
+  VIXL_ASSERT(CanAddressMemory());
+  const Instruction* pc_value = debugger->pc();
+  uint8_t* address = NULL;
+  memcpy(&address, &pc_value, sizeof(address));
+  return address;
+}
+
+void IdentifierToken::Print(FILE* out) const {
+  fprintf(out, "[Identifier %s]", value());
+}
+
+
+Token* IdentifierToken::Tokenize(const char* arg) {
+  if (!isalpha(arg[0])) {
+    return NULL;
+  }
+
+  const char* cursor = arg + 1;
+  while ((*cursor != '\0') && isalnum(*cursor)) {
+    ++cursor;
+  }
+
+  if (*cursor == '\0') {
+    return js_new<IdentifierToken>(arg);
+  }
+
+  return NULL;
+}
+
+
+uint8_t* AddressToken::ToAddress(Debugger* debugger) const {
+  USE(debugger);
+  return value();
+}
+
+
+void AddressToken::Print(FILE* out) const {
+  fprintf(out, "[Address %p]", value());
+}
+
+
+Token* AddressToken::Tokenize(const char* arg) {
+  if ((strlen(arg) < 3) || (arg[0] != '0') || (arg[1] != 'x')) {
+    return NULL;
+  }
+
+  uint64_t ptr = 0;
+  if (!StringToUInt64(&ptr, arg, 16)) {
+    return NULL;
+  }
+
+  uint8_t* address = reinterpret_cast<uint8_t*>(ptr);
+  return js_new<AddressToken>(address);
+}
+
+
+void IntegerToken::Print(FILE* out) const {
+  fprintf(out, "[Integer %" PRId64 "]", value());
+}
+
+
+Token* IntegerToken::Tokenize(const char* arg) {
+  int64_t value = 0;
+  if (!StringToInt64(&value, arg)) {
+    return NULL;
+  }
+
+  return js_new<IntegerToken>(value);
+}
+
+
+Token* FormatToken::Tokenize(const char* arg) {
+  size_t length = strlen(arg);
+  switch (arg[0]) {
+    case 'x':
+    case 's':
+    case 'u':
+    case 'f':
+      if (length == 1) return NULL;
+      break;
+    case 'i':
+      if (length == 1) return js_new<Format<uint32_t>>("%08" PRIx32, 'i');
+      VIXL_FALLTHROUGH();
+    default: return NULL;
+  }
+
+  char* endptr = NULL;
+  errno = 0;  // Reset errors.
+  uint64_t count = strtoul(arg + 1, &endptr, 10);
+
+  if (errno != 0) {
+    // Overflow, etc.
+    return NULL;
+  }
+
+  if (endptr == arg) {
+    // No digits were parsed.
+    return NULL;
+  }
+
+  if (*endptr != '\0') {
+    // There are unexpected (non-digit) characters after the number.
+    return NULL;
+  }
+
+  switch (arg[0]) {
+    case 'x':
+      switch (count) {
+        case 8: return js_new<Format<uint8_t>>("%02" PRIx8, 'x');
+        case 16: return js_new<Format<uint16_t>>("%04" PRIx16, 'x');
+        case 32: return js_new<Format<uint32_t>>("%08" PRIx32, 'x');
+        case 64: return js_new<Format<uint64_t>>("%016" PRIx64, 'x');
+        default: return NULL;
+      }
+    case 's':
+      switch (count) {
+        case 8: return js_new<Format<int8_t>>("%4" PRId8, 's');
+        case 16: return js_new<Format<int16_t>>("%6" PRId16, 's');
+        case 32: return js_new<Format<int32_t>>("%11" PRId32, 's');
+        case 64: return js_new<Format<int64_t>>("%20" PRId64, 's');
+        default: return NULL;
+      }
+    case 'u':
+      switch (count) {
+        case 8: return js_new<Format<uint8_t>>("%3" PRIu8, 'u');
+        case 16: return js_new<Format<uint16_t>>("%5" PRIu16, 'u');
+        case 32: return js_new<Format<uint32_t>>("%10" PRIu32, 'u');
+        case 64: return js_new<Format<uint64_t>>("%20" PRIu64, 'u');
+        default: return NULL;
+      }
+    case 'f':
+      switch (count) {
+        case 32: return js_new<Format<float>>("%13g", 'f');
+        case 64: return js_new<Format<double>>("%13g", 'f');
+        default: return NULL;
+      }
+    default:
+      VIXL_UNREACHABLE();
+      return NULL;
+  }
+}
+
+
+template<typename T>
+void Format<T>::Print(FILE* out) const {
+  unsigned size = sizeof(T) * 8;
+  fprintf(out, "[Format %c%u - %s]", type_code_, size, fmt_);
+}
+
+
+void UnknownToken::Print(FILE* out) const {
+  fprintf(out, "[Unknown %s]", unknown_);
+}
+
+
+void DebugCommand::Print(FILE* out) {
+  fprintf(out, "%s", name());
+}
+
+
+bool DebugCommand::Match(const char* name, const char** aliases) {
+  for (const char** current = aliases; *current != NULL; current++) {
+    if (strcmp(name, *current) == 0) {
+       return true;
+    }
+  }
+
+  return false;
+}
+
+
+DebugCommand* DebugCommand::Parse(char* line) {
+  TokenVector args;
+
+  for (char* chunk = strtok(line, " \t");
+       chunk != NULL;
+       chunk = strtok(NULL, " \t")) {
+    char* dot = strchr(chunk, '.');
+    if (dot != NULL) {
+      // 'Token.format'.
+      Token* format = FormatToken::Tokenize(dot + 1);
+      if (format != NULL) {
+        *dot = '\0';
+        args.append(Token::Tokenize(chunk));
+        args.append(format);
+      } else {
+        // Error while parsing the format, push the UnknownToken so an error
+        // can be accurately reported.
+        args.append(Token::Tokenize(chunk));
+      }
+    } else {
+      args.append(Token::Tokenize(chunk));
+    }
+  }
+
+  if (args.empty()) {
+    return NULL;
+  }
+
+  if (!args[0]->IsIdentifier()) {
+    return js_new<InvalidCommand>(Move(args), 0, "command name is not valid");
+  }
+
+  const char* name = IdentifierToken::Cast(args[0])->value();
+  #define RETURN_IF_MATCH(Command)       \
+  if (Match(name, Command::kAliases)) {  \
+    return Command::Build(Move(args));   \
+  }
+  DEBUG_COMMAND_LIST(RETURN_IF_MATCH);
+  #undef RETURN_IF_MATCH
+
+  return js_new<UnknownCommand>(Move(args));
+}
+
+
+void DebugCommand::PrintHelp(const char** aliases,
+                             const char* args,
+                             const char* help) {
+  VIXL_ASSERT(aliases[0] != NULL);
+  VIXL_ASSERT(help != NULL);
+
+  printf("\n----\n\n");
+  for (const char** current = aliases; *current != NULL; current++) {
+    if (args != NULL) {
+      printf("%s %s\n", *current, args);
+    } else {
+      printf("%s\n", *current);
+    }
+  }
+  printf("\n%s\n", help);
+}
+
+
+bool HelpCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+  USE(debugger);
+
+  #define PRINT_HELP(Command)                     \
+    DebugCommand::PrintHelp(Command::kAliases,    \
+                            Command::kArguments,  \
+                            Command::kHelp);
+  DEBUG_COMMAND_LIST(PRINT_HELP);
+  #undef PRINT_HELP
+  printf("\n----\n\n");
+
+  return false;
+}
+
+
+DebugCommand* HelpCommand::Build(TokenVector&& args) {
+  if (args.length() != 1) {
+    return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  return js_new<HelpCommand>(args[0]);
+}
+
+
+bool ContinueCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+
+  debugger->set_debug_parameters(debugger->debug_parameters() & ~DBG_ACTIVE);
+  return true;
+}
+
+
+DebugCommand* ContinueCommand::Build(TokenVector&& args) {
+  if (args.length() != 1) {
+    return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  return js_new<ContinueCommand>(args[0]);
+}
+
+
+bool StepCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+
+  int64_t steps = count();
+  if (steps < 0) {
+    printf(" ** invalid value for steps: %" PRId64 " (<0) **\n", steps);
+  } else if (steps > 1) {
+    debugger->set_steps(steps - 1);
+  }
+
+  return true;
+}
+
+
+void StepCommand::Print(FILE* out) {
+  fprintf(out, "%s %" PRId64 "", name(), count());
+}
+
+
+DebugCommand* StepCommand::Build(TokenVector&& args) {
+  IntegerToken* count = NULL;
+  switch (args.length()) {
+    case 1: {  // step [1]
+      count = js_new<IntegerToken>(1);
+      break;
+    }
+    case 2: {  // step n
+      Token* first = args[1];
+      if (!first->IsInteger()) {
+        return js_new<InvalidCommand>(Move(args), 1, "expects int");
+      }
+      count = IntegerToken::Cast(first);
+      break;
+    }
+    default:
+      return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  return js_new<StepCommand>(args[0], count);
+}
+
+
+DebugCommand* DisasmCommand::Build(TokenVector&& args) {
+  IntegerToken* count = NULL;
+  switch (args.length()) {
+    case 1: {  // disasm [10]
+      count = js_new<IntegerToken>(10);
+      break;
+    }
+    case 2: {  // disasm n
+      Token* first = args[1];
+      if (!first->IsInteger()) {
+        return js_new<InvalidCommand>(Move(args), 1, "expects int");
+      }
+
+      count = IntegerToken::Cast(first);
+      break;
+    }
+    default:
+      return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  Token* target = js_new<IdentifierToken>("pc");
+  FormatToken* format = js_new<Format<uint32_t>>("%08" PRIx32, 'i');
+  return js_new<ExamineCommand>(args[0], target, format, count);
+}
+
+
+void PrintCommand::Print(FILE* out) {
+  fprintf(out, "%s ", name());
+  target()->Print(out);
+  if (format() != NULL) format()->Print(out);
+}
+
+
+bool PrintCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+
+  Token* tok = target();
+  if (tok->IsIdentifier()) {
+    char* identifier = IdentifierToken::Cast(tok)->value();
+    if (strcmp(identifier, "regs") == 0) {
+      debugger->PrintRegisters();
+    } else if (strcmp(identifier, "fpregs") == 0) {
+      debugger->PrintVRegisters();
+    } else if (strcmp(identifier, "sysregs") == 0) {
+      debugger->PrintSystemRegisters();
+    } else if (strcmp(identifier, "pc") == 0) {
+      printf("pc = %16p\n", reinterpret_cast<const void*>(debugger->pc()));
+    } else {
+      printf(" ** Unknown identifier to print: %s **\n", identifier);
+    }
+
+    return false;
+  }
+
+  FormatToken* format_tok = format();
+  VIXL_ASSERT(format_tok != NULL);
+  if (format_tok->type_code() == 'i') {
+    // TODO(all): Add support for instruction disassembly.
+    printf(" ** unsupported format: instructions **\n");
+    return false;
+  }
+
+  if (tok->IsRegister()) {
+    RegisterToken* reg_tok = RegisterToken::Cast(tok);
+    Register reg = reg_tok->value();
+    debugger->PrintRegister(reg, reg_tok->Name(), format_tok);
+    return false;
+  }
+
+  if (tok->IsFPRegister()) {
+    FPRegister fpreg = FPRegisterToken::Cast(tok)->value();
+    debugger->PrintFPRegister(fpreg, format_tok);
+    return false;
+  }
+
+  VIXL_UNREACHABLE();
+  return false;
+}
+
+
+DebugCommand* PrintCommand::Build(TokenVector&& args) {
+  if (args.length() < 2) {
+    return js_new<InvalidCommand>(Move(args), -1, "too few arguments");
+  }
+
+  Token* target = args[1];
+  if (!target->IsRegister() &&
+      !target->IsFPRegister() &&
+      !target->IsIdentifier()) {
+    return js_new<InvalidCommand>(Move(args), 1, "expects reg or identifier");
+  }
+
+  FormatToken* format = NULL;
+  int target_size = 0;
+  if (target->IsRegister()) {
+    Register reg = RegisterToken::Cast(target)->value();
+    target_size = reg.SizeInBytes();
+  } else if (target->IsFPRegister()) {
+    FPRegister fpreg = FPRegisterToken::Cast(target)->value();
+    target_size = fpreg.SizeInBytes();
+  }
+  // If the target is an identifier there must be no format. This is checked
+  // in the switch statement below.
+
+  switch (args.length()) {
+    case 2: {
+      if (target->IsRegister()) {
+        switch (target_size) {
+          case 4: format = js_new<Format<uint32_t>>("%08" PRIx32, 'x'); break;
+          case 8: format = js_new<Format<uint64_t>>("%016" PRIx64, 'x'); break;
+          default: VIXL_UNREACHABLE();
+        }
+      } else if (target->IsFPRegister()) {
+        switch (target_size) {
+          case 4: format = js_new<Format<float>>("%8g", 'f'); break;
+          case 8: format = js_new<Format<double>>("%8g", 'f'); break;
+          default: VIXL_UNREACHABLE();
+        }
+      }
+      break;
+    }
+    case 3: {
+      if (target->IsIdentifier()) {
+        return js_new<InvalidCommand>(Move(args), 2,
+            "format is only allowed with registers");
+      }
+
+      Token* second = args[2];
+      if (!second->IsFormat()) {
+        return js_new<InvalidCommand>(Move(args), 2, "expects format");
+      }
+      format = FormatToken::Cast(second);
+
+      if (format->SizeOf() > target_size) {
+        return js_new<InvalidCommand>(Move(args), 2, "format too wide");
+      }
+
+      break;
+    }
+    default:
+      return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  return js_new<PrintCommand>(args[0], target, format);
+}
+
+
+bool ExamineCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+
+  uint8_t* address = target()->ToAddress(debugger);
+  int64_t  amount = count()->value();
+  if (format()->type_code() == 'i') {
+    debugger->PrintInstructions(address, amount);
+  } else {
+    debugger->PrintMemory(address, format(), amount);
+  }
+
+  return false;
+}
+
+
+void ExamineCommand::Print(FILE* out) {
+  fprintf(out, "%s ", name());
+  format()->Print(out);
+  target()->Print(out);
+}
+
+
+DebugCommand* ExamineCommand::Build(TokenVector&& args) {
+  if (args.length() < 2) {
+    return js_new<InvalidCommand>(Move(args), -1, "too few arguments");
+  }
+
+  Token* target = args[1];
+  if (!target->CanAddressMemory()) {
+    return js_new<InvalidCommand>(Move(args), 1, "expects address");
+  }
+
+  FormatToken* format = NULL;
+  IntegerToken* count = NULL;
+
+  switch (args.length()) {
+    case 2: {  // mem addr[.x64] [10]
+      format = js_new<Format<uint64_t>>("%016" PRIx64, 'x');
+      count = js_new<IntegerToken>(10);
+      break;
+    }
+    case 3: {  // mem addr.format [10]
+               // mem addr[.x64] n
+      Token* second = args[2];
+      if (second->IsFormat()) {
+        format = FormatToken::Cast(second);
+        count = js_new<IntegerToken>(10);
+        break;
+      } else if (second->IsInteger()) {
+        format = js_new<Format<uint64_t>>("%016" PRIx64, 'x');
+        count = IntegerToken::Cast(second);
+      } else {
+        return js_new<InvalidCommand>(Move(args), 2, "expects format or integer");
+      }
+      VIXL_UNREACHABLE();
+      break;
+    }
+    case 4: {  // mem addr.format n
+      Token* second = args[2];
+      Token* third = args[3];
+      if (!second->IsFormat() || !third->IsInteger()) {
+        return js_new<InvalidCommand>(Move(args), -1, "expects addr[.format] [n]");
+      }
+      format = FormatToken::Cast(second);
+      count = IntegerToken::Cast(third);
+      break;
+    }
+    default:
+      return js_new<InvalidCommand>(Move(args), -1, "too many arguments");
+  }
+
+  return js_new<ExamineCommand>(args[0], target, format, count);
+}
+
+
+UnknownCommand::~UnknownCommand() {
+  const size_t size = args_.length();
+  for (size_t i = 0; i < size; ++i) {
+    js_delete(args_[i]);
+  }
+}
+
+
+bool UnknownCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+  USE(debugger);
+
+  printf(" ** Unknown Command:");
+  const size_t size = args_.length();
+  for (size_t i = 0; i < size; ++i) {
+    printf(" ");
+    args_[i]->Print(stdout);
+  }
+  printf(" **\n");
+
+  return false;
+}
+
+
+InvalidCommand::~InvalidCommand() {
+  const size_t size = args_.length();
+  for (size_t i = 0; i < size; ++i) {
+    js_delete(args_[i]);
+  }
+}
+
+
+bool InvalidCommand::Run(Debugger* debugger) {
+  VIXL_ASSERT(debugger->IsDebuggerRunning());
+  USE(debugger);
+
+  printf(" ** Invalid Command:");
+  const size_t size = args_.length();
+  for (size_t i = 0; i < size; ++i) {
+    printf(" ");
+    if (i == static_cast<size_t>(index_)) {
+      printf(">>");
+      args_[i]->Print(stdout);
+      printf("<<");
+    } else {
+      args_[i]->Print(stdout);
+    }
+  }
+  printf(" **\n");
+  printf(" ** %s\n", cause_);
+
+  return false;
+}
+
+}  // namespace vixl
+
+#endif  // JS_SIMULATOR_ARM64