Bump the C stack pointer when building Dart frames to maintain the ARM64 ABI requirements without g…

runtime/vm/assembler_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 1108 matching lines @@
   ldr(TMP, FieldAddress(CODE_REG, Code::saved_instructions_offset()));
   cmp(R0, Operand(TMP));
   b(&instructions_ok, EQ);
   brk(1);
   Bind(&instructions_ok);
   Pop(R0);
 #endif
 }
 
 
+void Assembler::SetupDartSP() {
+  mov(SP, CSP);
+}
+
+
+void Assembler::RestoreCSP() {
+  mov(CSP, SP);
+}
+
+
 void Assembler::EnterFrame(intptr_t frame_size) {
+  // The ARM64 ABI requires at all times
+  //   - stack limit < CSP <= stack base
+  //   - CSP mod 16 = 0
+  //   - we do not access stack memory below CSP
+  // Pratically, this means we need to keep the C stack pointer ahead of the
+  // Dart stack pointer and 16-byte aligned for signal handlers. If we knew the
+  // real stack limit, we could just set CSP to a value near it during
+  // SetupDartSP, but we do not know the real stack limit for the initial
+  // thread or threads created by the embedder.
+  // TODO(26472): It would be safer to use CSP as the Dart stack pointer, but
+  // this requires adjustments to stack handling to maintain the 16-byte
+  // alignment.
+  const intptr_t kMaxDartFrameSize = 4096;
+  sub(TMP, SP, Operand(kMaxDartFrameSize));
+  andi(CSP, TMP, Immediate(~15));
+
   PushPair(LR, FP);
   mov(FP, SP);
 
   if (frame_size > 0) {
     sub(SP, SP, Operand(frame_size));
   }
 }
 
 
 void Assembler::LeaveFrame() {
@@ skipping 305 matching lines @@
     add(base, array, Operand(index, LSL, shift));
   }
   const OperandSize size = Address::OperandSizeFor(cid);
   ASSERT(Address::CanHoldOffset(offset, Address::Offset, size));
   return Address(base, offset, Address::Offset, size);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64