Arm64: Ensure that csp is always aligned to 16 byte values even if jssp is not.

src/arm64/macro-assembler-arm64.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARM64_MACRO_ASSEMBLER_ARM64_H_
 #define V8_ARM64_MACRO_ASSEMBLER_ARM64_H_
 
 #include <vector>
 
 #include "v8globals.h"
@@ skipping 760 matching lines @@
     Bic(csp, StackPointer(), sp_alignment - 1);
     SetStackPointer(csp);
   }
 
   // Push the system stack pointer (csp) down to allow the same to be done to
   // the current stack pointer (according to StackPointer()). This must be
   // called _before_ accessing the memory.
   //
   // This is necessary when pushing or otherwise adding things to the stack, to
   // satisfy the AAPCS64 constraint that the memory below the system stack
-  // pointer is not accessed.
+  // pointer is not accessed.  The amount pushed will be increased as necessary
+  // to ensure csp remains aligned to 16 bytes.
   //
   // This method asserts that StackPointer() is not csp, since the call does
   // not make sense in that context.
   inline void BumpSystemStackPointer(const Operand& space);
 
+  // Re-synchronizes the system stack pointer (csp) with the current stack
+  // pointer (according to StackPointer()).  This function will ensure the
+  // new value of the system stack pointer is remains aligned to 16 bytes, and
+  // is lower than or equal to the value of the current stack pointer.
+  //
+  // This method asserts that StackPointer() is not csp, since the call does
+  // not make sense in that context.
+  inline void SyncSystemStackPointer();
+
   // Helpers ------------------------------------------------------------------
   // Root register.
   inline void InitializeRootRegister();
 
   // Load an object from the root table.
   void LoadRoot(CPURegister destination,
                 Heap::RootListIndex index);
   // Store an object to the root table.
   void StoreRoot(Register source,
                  Heap::RootListIndex index);
@@ skipping 1487 matching lines @@
 #error "Unsupported option"
 #define CODE_COVERAGE_STRINGIFY(x) #x
 #define CODE_COVERAGE_TOSTRING(x) CODE_COVERAGE_STRINGIFY(x)
 #define __FILE_LINE__ __FILE__ ":" CODE_COVERAGE_TOSTRING(__LINE__)
 #define ACCESS_MASM(masm) masm->stop(__FILE_LINE__); masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 #endif  // V8_ARM64_MACRO_ASSEMBLER_ARM64_H_