[snapshot] do not embed string addresses in code.

Doing so in a -pie build would make the snapshot non-deterministic.

R=bmeurer@chromium.org
BUG=v8:5233

Review-Url: https://codereview.chromium.org/2178093003
Cr-Commit-Position: refs/heads/master@{#38042}

src/arm/assembler-arm.cc

@@ -2164,7 +2164,11 @@ void Assembler::stop(const char* msg, Condition cond, int32_t code) {
     } else {
       svc(kStopCode + kMaxStopCode, cond);
     }
-    emit(reinterpret_cast<Instr>(msg));
+    // Do not embed the message string address! We used to do this, but that
+    // made snapshots created from position-independent executable builds
+    // non-deterministic.
+    // TODO(yangguo): remove this field entirely.
+    nop();
   }
 #else  // def __arm__
   if (cond != al) {

src/arm/disasm-arm.cc

@@ -1364,16 +1364,10 @@ int Decoder::DecodeType7(Instruction* instr) {
   if (instr->Bit(24) == 1) {
     if (instr->SvcValue() >= kStopCode) {
       Format(instr, "stop'cond 'svc");
-      // Also print the stop message. Its address is encoded
-      // in the following 4 bytes.
-      out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
-                                  "\n  %p  %08x       stop message: %s",
-                                  reinterpret_cast<void*>(instr
-                                                 + Instruction::kInstrSize),
-                                  *reinterpret_cast<uint32_t*>(instr
-                                                + Instruction::kInstrSize),
-                                  *reinterpret_cast<char**>(instr
-                                                + Instruction::kInstrSize));
+      out_buffer_pos_ += SNPrintF(
+          out_buffer_ + out_buffer_pos_, "\n  %p  %08x",
+          reinterpret_cast<void*>(instr + Instruction::kInstrSize),
+          *reinterpret_cast<uint32_t*>(instr + Instruction::kInstrSize));
       // We have decoded 2 * Instruction::kInstrSize bytes.
       return 2 * Instruction::kInstrSize;
     } else {

src/arm/simulator-arm.cc

@@ -115,18 +115,11 @@ static void InitializeCoverage() {
 void ArmDebugger::Stop(Instruction* instr) {
   // Get the stop code.
   uint32_t code = instr->SvcValue() & kStopCodeMask;
-  // Retrieve the encoded address, which comes just after this stop.
-  char* msg = *reinterpret_cast<char**>(sim_->get_pc()
-                                        + Instruction::kInstrSize);
-  // Update this stop description.
-  if (sim_->isWatchedStop(code) && !sim_->watched_stops_[code].desc) {
-    sim_->watched_stops_[code].desc = msg;
-  }
   // Print the stop message and code if it is not the default code.
   if (code != kMaxStopCode) {
-    PrintF("Simulator hit stop %u: %s\n", code, msg);
+    PrintF("Simulator hit stop %u\n", code);
   } else {
-    PrintF("Simulator hit %s\n", msg);
+    PrintF("Simulator hit\n");
   }
   sim_->set_pc(sim_->get_pc() + 2 * Instruction::kInstrSize);
   Debug();

src/mips/assembler-mips.cc

@@ -1974,7 +1974,11 @@ void Assembler::stop(const char* msg, uint32_t code) {
   // The Simulator will handle the stop instruction and get the message address.
   // On MIPS stop() is just a special kind of break_().
   break_(code, true);
-  emit(reinterpret_cast<Instr>(msg));
+  // Do not embed the message string address! We used to do this, but that
+  // made snapshots created from position-independent executable builds
+  // non-deterministic.
+  // TODO(yangguo): remove this field entirely.
+  nop();
 #endif
 }
 

src/mips/simulator-mips.cc

@@ -138,14 +138,7 @@ static void InitializeCoverage() {}
 void MipsDebugger::Stop(Instruction* instr) {
   // Get the stop code.
   uint32_t code = instr->Bits(25, 6);
-  // Retrieve the encoded address, which comes just after this stop.
-  char* msg = *reinterpret_cast<char**>(sim_->get_pc() +
-      Instruction::kInstrSize);
-  // Update this stop description.
-  if (!sim_->watched_stops_[code].desc) {
-    sim_->watched_stops_[code].desc = msg;
-  }
-  PrintF("Simulator hit %s (%u)\n", msg, code);
+  PrintF("Simulator hit (%u)\n", code);
   sim_->set_pc(sim_->get_pc() + 2 * Instruction::kInstrSize);
   Debug();
 }

src/mips64/assembler-mips64.cc

@@ -2225,7 +2225,11 @@ void Assembler::stop(const char* msg, uint32_t code) {
   // The Simulator will handle the stop instruction and get the message address.
   // On MIPS stop() is just a special kind of break_().
   break_(code, true);
-  emit(reinterpret_cast<uint64_t>(msg));
+  // Do not embed the message string address! We used to do this, but that
+  // made snapshots created from position-independent executable builds
+  // non-deterministic.
+  // TODO(yangguo): remove this field entirely.
+  nop();
 #endif
 }
 

src/mips64/disasm-mips64.cc

@@ -803,13 +803,11 @@ int Decoder::DecodeBreakInstr(Instruction* instr) {
     // This is stop(msg).
     Format(instr, "break, code: 'code");
     out_buffer_pos_ += SNPrintF(
-        out_buffer_ + out_buffer_pos_,
-        "\n%p       %08" PRIx64 "       stop msg: %s",
+        out_buffer_ + out_buffer_pos_, "\n%p       %08" PRIx64,
         static_cast<void*>(
             reinterpret_cast<int32_t*>(instr + Instruction::kInstrSize)),
         reinterpret_cast<uint64_t>(
-            *reinterpret_cast<char**>(instr + Instruction::kInstrSize)),
-        *reinterpret_cast<char**>(instr + Instruction::kInstrSize));
+            *reinterpret_cast<char**>(instr + Instruction::kInstrSize)));
     // Size 3: the break_ instr, plus embedded 64-bit char pointer.
     return 3 * Instruction::kInstrSize;
   } else {

src/mips64/simulator-mips64.cc

@@ -152,14 +152,7 @@ static void InitializeCoverage() {}
 void MipsDebugger::Stop(Instruction* instr) {
   // Get the stop code.
   uint32_t code = instr->Bits(25, 6);
-  // Retrieve the encoded address, which comes just after this stop.
-  char* msg = *reinterpret_cast<char**>(sim_->get_pc() +
-      Instruction::kInstrSize);
-  // Update this stop description.
-  if (!sim_->watched_stops_[code].desc) {
-    sim_->watched_stops_[code].desc = msg;
-  }
-  PrintF("Simulator hit %s (%u)\n", msg, code);
+  PrintF("Simulator hit (%u)\n", code);
   // TODO(yuyin): 2 -> 3?
   sim_->set_pc(sim_->get_pc() + 3 * Instruction::kInstrSize);
   Debug();