[runtime] Reset the current context when leaving the runtime in the CEntryStub

This CL introduces a Context::kInvalidContext sentinel value to make clear that
no context is active. We silently accept smi 0 (= nullptr) as a non-set context
which usually was the default value making it hard to ensure whether this
happened on purpose or not.


Change-Id: I5c35616f26b0b64c1cd976563a6eeb0ce474927d
Reviewed-on: https://chromium-review.googlesource.com/790291Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49778}

src/arm/macro-assembler-arm.cc

@@ -1218,7 +1218,6 @@ int TurboAssembler::ActivationFrameAlignment() {
 #endif  // V8_HOST_ARCH_ARM
 }
 
-
 void MacroAssembler::LeaveExitFrame(bool save_doubles, Register argument_count,
                                     bool argument_count_is_length) {
   ConstantPoolUnavailableScope constant_pool_unavailable(this);
@@ -1244,6 +1243,7 @@ void MacroAssembler::LeaveExitFrame(bool save_doubles, Register argument_count,
       Operand(ExternalReference(IsolateAddressId::kContextAddress, isolate())));
   ldr(cp, MemOperand(scratch));
 #ifdef DEBUG
+  mov(r3, Operand(Context::kInvalidContext));
   mov(scratch,
       Operand(ExternalReference(IsolateAddressId::kContextAddress, isolate())));
   str(r3, MemOperand(scratch));

src/arm64/code-stubs-arm64.cc

@@ -415,7 +415,7 @@ void CEntryStub::Generate(MacroAssembler* masm) {
   __ Peek(argc, 2 * kPointerSize);
   __ Peek(target, 3 * kPointerSize);
 
-  __ LeaveExitFrame(save_doubles(), x10);
+  __ LeaveExitFrame(save_doubles(), x10, x9);
   DCHECK(jssp.Is(__ StackPointer()));
   if (!argv_in_register()) {
     // Drop the remaining stack slots and return from the stub.
@@ -1218,7 +1218,7 @@ static void CallApiFunctionAndReturn(MacroAssembler* masm,
   __ Peek(x21, (spill_offset + 2) * kXRegSize);
   __ Peek(x22, (spill_offset + 3) * kXRegSize);
 
-  __ LeaveExitFrame(false, x1);
+  __ LeaveExitFrame(false, x1, x5);
 
   // Check if the function scheduled an exception.
   __ Mov(x5, ExternalReference::scheduled_exception_address(isolate));

src/arm64/macro-assembler-arm64.cc

@@ -2638,7 +2638,8 @@ void MacroAssembler::EnterExitFrame(bool save_doubles, const Register& scratch,
 
 // Leave the current exit frame.
 void MacroAssembler::LeaveExitFrame(bool restore_doubles,
-                                    const Register& scratch) {
+                                    const Register& scratch,
+                                    const Register& scratch2) {
   DCHECK(csp.Is(StackPointer()));
 
   if (restore_doubles) {
@@ -2652,9 +2653,10 @@ void MacroAssembler::LeaveExitFrame(bool restore_doubles,
 
   if (emit_debug_code()) {
     // Also emit debug code to clear the cp in the top frame.
+    Mov(scratch2, Operand(Context::kInvalidContext));
     Mov(scratch, Operand(ExternalReference(IsolateAddressId::kContextAddress,
                                            isolate())));
-    Str(xzr, MemOperand(scratch));
+    Str(scratch2, MemOperand(scratch));
   }
   // Clear the frame pointer from the top frame.
   Mov(scratch, Operand(ExternalReference(IsolateAddressId::kCEntryFPAddress,

src/arm64/macro-assembler-arm64.h

@@ -1992,7 +1992,8 @@ class MacroAssembler : public TurboAssembler {
   //  * The stack pointer is reset to jssp.
   //
   // The stack pointer must be csp on entry.
-  void LeaveExitFrame(bool save_doubles, const Register& scratch);
+  void LeaveExitFrame(bool save_doubles, const Register& scratch,
+                      const Register& scratch2);
 
   // Load the global proxy from the current context.
   void LoadGlobalProxy(Register dst) {

src/code-stub-assembler.cc

@@ -175,7 +175,9 @@ Node* CodeStubAssembler::SelectSmiConstant(Node* condition, Smi* true_value,
                         MachineRepresentation::kTaggedSigned);
 }
 
-Node* CodeStubAssembler::NoContextConstant() { return SmiConstant(0); }
+Node* CodeStubAssembler::NoContextConstant() {
+  return SmiConstant(Context::kNoContext);
+}
 
 #define HEAP_CONSTANT_ACCESSOR(rootIndexName, rootAccessorName, name) \
   compiler::TNode<std::remove_reference<decltype(                     \

src/contexts.h

@@ -566,6 +566,9 @@ class Context: public FixedArray {
   static const int FIRST_FUNCTION_MAP_INDEX = SLOPPY_FUNCTION_MAP_INDEX;
   static const int LAST_FUNCTION_MAP_INDEX = CLASS_FUNCTION_MAP_INDEX;
 
+  static const int kNoContext = 0;
+  static const int kInvalidContext = 1;
+
   void ResetErrorsThrown();
   void IncrementErrorsThrown();
   int GetErrorsThrown();

src/ia32/macro-assembler-ia32.cc

@@ -738,7 +738,8 @@ void MacroAssembler::LeaveExitFrameEpilogue() {
                                     isolate());
   mov(esi, Operand::StaticVariable(context_address));
 #ifdef DEBUG
-  mov(Operand::StaticVariable(context_address), Immediate(0));
+  mov(Operand::StaticVariable(context_address),
+      Immediate(Context::kInvalidContext));
 #endif
 
   // Clear the top frame.

src/x64/macro-assembler-x64.cc

@@ -2548,7 +2548,7 @@ void MacroAssembler::LeaveExitFrameEpilogue() {
   Operand context_operand = ExternalOperand(context_address);
   movp(rsi, context_operand);
 #ifdef DEBUG
-  movp(context_operand, Immediate(0));
+  movp(context_operand, Immediate(Context::kInvalidContext));
 #endif
 
   // Clear the top frame.