[Atomics] Implement ldaxr/stlxr instructions in ARM64 simulator

src/arm64/simulator-arm64.cc

Index: src/arm64/simulator-arm64.cc
diff --git a/src/arm64/simulator-arm64.cc b/src/arm64/simulator-arm64.cc
index 83b4cf7ee8954f0838a8389eb3a5c971558eb5a2..a5ced87c420d6fe7e95c6bf4f42b018b7078e844 100644
--- a/src/arm64/simulator-arm64.cc
+++ b/src/arm64/simulator-arm64.cc
@@ -55,6 +55,9 @@ TEXT_COLOUR clr_debug_number   = FLAG_log_colour ? COLOUR_BOLD(YELLOW)  : "";
 TEXT_COLOUR clr_debug_message  = FLAG_log_colour ? COLOUR(YELLOW)       : "";
 TEXT_COLOUR clr_printf         = FLAG_log_colour ? COLOUR(GREEN)        : "";
 
+// static
+base::LazyInstance<Simulator::GlobalMonitor>::type Simulator::global_monitor_ =
+    LAZY_INSTANCE_INITIALIZER;
 
 // This is basically the same as PrintF, with a guard for FLAG_trace_sim.
 void Simulator::TraceSim(const char* format, ...) {
@@ -429,6 +432,7 @@ void Simulator::ResetState() {
 
 
 Simulator::~Simulator() {
+  global_monitor_.Pointer()->RemoveProcessor(&global_monitor_processor_);
   delete[] reinterpret_cast<byte*>(stack_);
   if (FLAG_log_instruction_stats) {
     delete instrument_;
@@ -1628,6 +1632,15 @@ void Simulator::LoadStoreHelper(Instruction* instr,
   uintptr_t address = LoadStoreAddress(addr_reg, offset, addrmode);
   uintptr_t stack = 0;
 
+  base::LockGuard<base::Mutex> lock_guard(&global_monitor_.Pointer()->mutex);
+  if (instr->IsLoad()) {
+    local_monitor_.NotifyLoad(address);
+  } else {
+    local_monitor_.NotifyStore(address);
+    global_monitor_.Pointer()->NotifyStore_Locked(address,
+                                                  &global_monitor_processor_);
+  }
+
   // Handle the writeback for stores before the store. On a CPU the writeback
   // and the store are atomic, but when running on the simulator it is possible
   // to be interrupted in between. The simulator is not thread safe and V8 does
@@ -1730,6 +1743,19 @@ void Simulator::LoadStorePairHelper(Instruction* instr,
   uintptr_t address2 = address + access_size;
   uintptr_t stack = 0;
 
+  base::LockGuard<base::Mutex> lock_guard(&global_monitor_.Pointer()->mutex);
+  if (instr->IsLoad()) {
+    local_monitor_.NotifyLoad(address);
+    local_monitor_.NotifyLoad(address2);
+  } else {
+    local_monitor_.NotifyStore(address);
+    local_monitor_.NotifyStore(address2);
+    global_monitor_.Pointer()->NotifyStore_Locked(address,
+                                                  &global_monitor_processor_);
+    global_monitor_.Pointer()->NotifyStore_Locked(address2,
+                                                  &global_monitor_processor_);
+  }
+
   // Handle the writeback for stores before the store. On a CPU the writeback
   // and the store are atomic, but when running on the simulator it is possible
   // to be interrupted in between. The simulator is not thread safe and V8 does
@@ -1853,6 +1879,9 @@ void Simulator::VisitLoadLiteral(Instruction* instr) {
   uintptr_t address = instr->LiteralAddress();
   unsigned rt = instr->Rt();
 
+  base::LockGuard<base::Mutex> lock_guard(&global_monitor_.Pointer()->mutex);
+  local_monitor_.NotifyLoad(address);
+
   switch (instr->Mask(LoadLiteralMask)) {
     // Use _no_log variants to suppress the register trace (LOG_REGS,
     // LOG_FP_REGS), then print a more detailed log.
@@ -1906,8 +1935,82 @@ void Simulator::LoadStoreWriteBack(unsigned addr_reg,
   }
 }
 
+Simulator::TransactionSize Simulator::get_transaction_size(unsigned size) {
+  switch (size) {
+    case 0:
+      return TransactionSize::None;
+    case 1:
+      return TransactionSize::Byte;
+    case 2:
+      return TransactionSize::HalfWord;
+    case 4:
+      return TransactionSize::Word;
+    default:
+      UNREACHABLE();
+  }
+  return TransactionSize::None;
+}
+
 void Simulator::VisitLoadStoreAcquireRelease(Instruction* instr) {
-  // TODO(binji)
+  unsigned rs = instr->Rs();
+  unsigned rt = instr->Rt();
+  unsigned rn = instr->Rn();
+  LoadStoreAcquireReleaseOp op = static_cast<LoadStoreAcquireReleaseOp>(
+      instr->Mask(LoadStoreAcquireReleaseMask));
+  bool is_acquire_release = instr->LoadStoreXAcquireRelease();
+  bool is_exclusive = !instr->LoadStoreXNotExclusive();

[jbramley, 2017/02/24 15:25:41]

These helpers return integers. Usually we would test (for example)
"instr->LoadStoreXAcquireRelease() != 0" rather than rely on the implicit
conversion.

[aseemgarg, 2017/02/24 22:38:49]

Done.

+  bool is_load = instr->LoadStoreXLoad();
+  bool is_pair = instr->LoadStoreXPair();
+  DCHECK(is_acquire_release);
+  DCHECK(is_exclusive);  // non exclusive unimplemented
+  DCHECK(!is_pair);      // pair unimplemented

[jbramley, 2017/02/24 15:25:41]

Capital letters, full stops.

[aseemgarg, 2017/02/24 22:38:49]

Done.

+  unsigned access_size = 1 << instr->LoadStoreXSizeLog2();
+  uintptr_t address = LoadStoreAddress(rn, 0, AddrMode::Offset);
+  DCHECK(address % access_size == 0);
+  if (is_load) {
+    base::LockGuard<base::Mutex> lock_guard(&global_monitor_.Pointer()->mutex);

[jbramley, 2017/02/24 15:25:41]

You lock the mutex in both paths, so perhaps factor it out.

[aseemgarg, 2017/02/24 22:38:49]

Done.

+    local_monitor_.NotifyLoadExcl(address, get_transaction_size(access_size));
+    global_monitor_.Pointer()->NotifyLoadExcl_Locked(
+        address, &global_monitor_processor_);
+    switch (op) {
+      case LDAXR_b:
+        set_wreg_no_log(rt, MemoryRead<uint8_t>(address));
+        break;
+      case LDAXR_h:
+        set_wreg_no_log(rt, MemoryRead<uint16_t>(address));
+        break;
+      case LDAXR_w:
+        set_wreg_no_log(rt, MemoryRead<uint32_t>(address));
+        break;
+      default:
+        UNIMPLEMENTED();
+    }
+    LogRead(address, access_size, rt);
+  } else {
+    base::LockGuard<base::Mutex> lock_guard(&global_monitor_.Pointer()->mutex);
+    if (local_monitor_.NotifyStoreExcl(address,
+                                       get_transaction_size(access_size)) &&
+        global_monitor_.Pointer()->NotifyStoreExcl_Locked(
+            address, &global_monitor_processor_)) {
+      switch (op) {
+        case STLXR_b:
+          MemoryWrite<uint8_t>(address, wreg(rt));
+          break;
+        case STLXR_h:
+          MemoryWrite<uint16_t>(address, wreg(rt));
+          break;
+        case STLXR_w:
+          MemoryWrite<uint32_t>(address, wreg(rt));
+          break;
+        default:
+          UNIMPLEMENTED();
+      }
+      LogWrite(address, access_size, rt);
+      set_wreg(rs, 0);
+    } else {
+      set_wreg(rs, 1);
+    }
+  }
 }
 
 void Simulator::CheckMemoryAccess(uintptr_t address, uintptr_t stack) {
@@ -3877,6 +3980,186 @@ void Simulator::DoPrintf(Instruction* instr) {
   delete[] format;
 }
 
+Simulator::LocalMonitor::LocalMonitor()
+    : access_state_(MonitorAccess::Open),
+      tagged_addr_(0),
+      size_(TransactionSize::None) {}
+
+void Simulator::LocalMonitor::Clear() {
+  access_state_ = MonitorAccess::Open;
+  tagged_addr_ = 0;
+  size_ = TransactionSize::None;
+}
+
+void Simulator::LocalMonitor::NotifyLoad(uintptr_t addr) {
+  if (access_state_ == MonitorAccess::Exclusive) {
+    // A non exclusive load could clear the local monitor. As a result, it's
+    // most strict to unconditionally clear the local monitor on load.
+    Clear();
+  }
+}
+
+void Simulator::LocalMonitor::NotifyLoadExcl(uintptr_t addr,
+                                             TransactionSize size) {
+  access_state_ = MonitorAccess::Exclusive;
+  tagged_addr_ = addr;
+  size_ = size;
+}
+
+void Simulator::LocalMonitor::NotifyStore(uintptr_t addr) {
+  if (access_state_ == MonitorAccess::Exclusive) {
+    // A non exclusive store could clear the local monitor. As a result, it's
+    // most strict to unconditionally clear the local monitor on store.
+    Clear();
+  }
+}
+
+bool Simulator::LocalMonitor::NotifyStoreExcl(uintptr_t addr,
+                                              TransactionSize size) {
+  if (access_state_ == MonitorAccess::Exclusive) {
+    // It is allowed for a processor to require that the address matches
+    // exactly (B2.10.1), so this comparison does not mask addr.
+    if (addr == tagged_addr_ && size_ == size) {
+      Clear();
+      return true;
+    } else {
+      // It is implementation-defined whether an exclusive store to a
+      // non-tagged address will update memory. As a result, it's most strict
+      // to unconditionally clear the local monitor.
+      Clear();
+      return false;
+    }
+  } else {
+    DCHECK(access_state_ == MonitorAccess::Open);
+    return false;
+  }
+}
+
+Simulator::GlobalMonitor::Processor::Processor()
+    : access_state_(MonitorAccess::Open),
+      tagged_addr_(0),
+      next_(nullptr),
+      prev_(nullptr),
+      failure_counter_(0) {}
+
+void Simulator::GlobalMonitor::Processor::Clear_Locked() {
+  access_state_ = MonitorAccess::Open;
+  tagged_addr_ = 0;
+}
+
+void Simulator::GlobalMonitor::Processor::NotifyLoadExcl_Locked(
+    uintptr_t addr) {
+  access_state_ = MonitorAccess::Exclusive;
+  tagged_addr_ = addr;
+}
+
+void Simulator::GlobalMonitor::Processor::NotifyStore_Locked(
+    uintptr_t addr, bool is_requesting_processor) {
+  if (access_state_ == MonitorAccess::Exclusive) {
+    // A non exclusive store could clear the global monitor. As a result, it's
+    // most strict to unconditionally clear global monitors on store.
+    Clear_Locked();
+  }
+}
+
+bool Simulator::GlobalMonitor::Processor::NotifyStoreExcl_Locked(
+    uintptr_t addr, bool is_requesting_processor) {
+  if (access_state_ == MonitorAccess::Exclusive) {
+    if (is_requesting_processor) {
+      // It is allowed for a processor to require that the address matches
+      // exactly (B2.10.2), so this comparison does not mask addr.
+      if (addr == tagged_addr_) {
+        Clear_Locked();
+        // Introduce occasional stxr failures. This is to simulate the
+        // behavior of hardware, which can randomly fail due to background
+        // cache evictions.
+        if (failure_counter_++ >= kMaxFailureCounter) {
+          failure_counter_ = 0;
+          return false;
+        } else {
+          return true;
+        }
+      }
+    } else if ((addr & kExclusiveTaggedAddrMask) ==
+               (tagged_addr_ & kExclusiveTaggedAddrMask)) {
+      // Check the masked addresses when responding to a successful lock by
+      // another processor so the implementation is more conservative (i.e. the
+      // granularity of locking is as large as possible.)
+      Clear_Locked();
+      return false;
+    }
+  }
+  return false;
+}
+
+Simulator::GlobalMonitor::GlobalMonitor() : head_(nullptr) {}
+
+void Simulator::GlobalMonitor::NotifyLoadExcl_Locked(uintptr_t addr,
+                                                     Processor* processor) {
+  processor->NotifyLoadExcl_Locked(addr);
+  PrependProcessor_Locked(processor);
+}
+
+void Simulator::GlobalMonitor::NotifyStore_Locked(uintptr_t addr,
+                                                  Processor* processor) {
+  // Notify each processor of the store operation.
+  for (Processor* iter = head_; iter; iter = iter->next_) {
+    bool is_requesting_processor = iter == processor;
+    iter->NotifyStore_Locked(addr, is_requesting_processor);
+  }
+}
+
+bool Simulator::GlobalMonitor::NotifyStoreExcl_Locked(uintptr_t addr,
+                                                      Processor* processor) {
+  DCHECK(IsProcessorInLinkedList_Locked(processor));
+  if (processor->NotifyStoreExcl_Locked(addr, true)) {
+    // Notify the other processors that this StoreExcl succeeded.
+    for (Processor* iter = head_; iter; iter = iter->next_) {
+      if (iter != processor) {
+        iter->NotifyStoreExcl_Locked(addr, false);
+      }
+    }
+    return true;
+  } else {
+    return false;
+  }
+}
+
+bool Simulator::GlobalMonitor::IsProcessorInLinkedList_Locked(
+    Processor* processor) const {
+  return head_ == processor || processor->next_ || processor->prev_;
+}
+
+void Simulator::GlobalMonitor::PrependProcessor_Locked(Processor* processor) {
+  if (IsProcessorInLinkedList_Locked(processor)) {
+    return;
+  }
+
+  if (head_) {
+    head_->prev_ = processor;
+  }
+  processor->prev_ = nullptr;
+  processor->next_ = head_;
+  head_ = processor;
+}
+
+void Simulator::GlobalMonitor::RemoveProcessor(Processor* processor) {
+  base::LockGuard<base::Mutex> lock_guard(&mutex);
+  if (!IsProcessorInLinkedList_Locked(processor)) {
+    return;
+  }
+
+  if (processor->prev_) {
+    processor->prev_->next_ = processor->next_;
+  } else {
+    head_ = processor->next_;
+  }
+  if (processor->next_) {
+    processor->next_->prev_ = processor->prev_;
+  }
+  processor->prev_ = nullptr;
+  processor->next_ = nullptr;
+}
 
 #endif  // USE_SIMULATOR