Set the current context to the function's context when entering to LAP.

src/s390/code-stubs-s390.cc

Index: src/s390/code-stubs-s390.cc
diff --git a/src/s390/code-stubs-s390.cc b/src/s390/code-stubs-s390.cc
index 533a63c8915b511c84c2cbaa267229e3aa162bac..cb8154e5ff416d0db24dee3dc251dd47079c1e59 100644
--- a/src/s390/code-stubs-s390.cc
+++ b/src/s390/code-stubs-s390.cc
@@ -2771,8 +2771,9 @@ void CallApiCallbackStub::Generate(MacroAssembler* masm) {
   //  --
   //  -- sp[0]               : last argument
   //  -- ...
-  //  -- sp[(argc - 1)* 4]   : first argument
+  //  -- sp[(argc - 1) * 4]  : first argument
   //  -- sp[argc * 4]        : receiver
+  //  -- sp[(argc + 1) * 4]  : accessor_holder
   // -----------------------------------
 
   Register callee = r2;
@@ -2798,10 +2799,6 @@ void CallApiCallbackStub::Generate(MacroAssembler* masm) {
 
   // context save
   __ push(context);
-  if (!is_lazy()) {
-    // load context from callee
-    __ LoadP(context, FieldMemOperand(callee, JSFunction::kContextOffset));
-  }
 
   // callee
   __ push(callee);
@@ -2821,6 +2818,20 @@ void CallApiCallbackStub::Generate(MacroAssembler* masm) {
   // holder
   __ push(holder);
 
+  // Enter a new context
+  if (is_lazy()) {
+    // Load context from accessor_holder
+    Register accessor_holder = context;
+    __ LoadP(accessor_holder,
+             MemOperand(sp, (FCA::kArgsLength + 1 + argc()) * kPointerSize));
+    __ LoadP(scratch, FieldMemOperand(accessor_holder, HeapObject::kMapOffset));
+    __ GetMapConstructor(scratch, scratch, context, callee);
+    __ LoadP(context, FieldMemOperand(scratch, JSFunction::kContextOffset));
+  } else {
+    // Load context from callee
+    __ LoadP(context, FieldMemOperand(callee, JSFunction::kContextOffset));
+  }
+
   // Prepare arguments.
   __ LoadRR(scratch, sp);
 
@@ -2865,12 +2876,8 @@ void CallApiCallbackStub::Generate(MacroAssembler* masm) {
     return_value_offset = 2 + FCA::kReturnValueOffset;
   }
   MemOperand return_value_operand(fp, return_value_offset * kPointerSize);
-  int stack_space = 0;
-  MemOperand length_operand =
-      MemOperand(sp, kFunctionCallbackInfoOffset + 2 * kPointerSize);
-  MemOperand* stack_space_operand = &length_operand;
-  stack_space = argc() + FCA::kArgsLength + 1;
-  stack_space_operand = NULL;
+  const int stack_space = argc() + FCA::kArgsLength + 2;
+  MemOperand* stack_space_operand = nullptr;
   CallApiFunctionAndReturn(masm, api_function_address, thunk_ref, stack_space,
                            stack_space_operand, return_value_operand,
                            &context_restore_operand);