Fixes to run "Hello, world!" on arm64 hardware.

runtime/vm/runtime_entry_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"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/runtime_entry.h"
 
 #include "vm/assembler.h"
@@ skipping 22 matching lines @@
   Simulator::CallKind call_kind =
       is_leaf() ? (is_float() ? Simulator::kLeafFloatRuntimeCall
                               : Simulator::kLeafRuntimeCall)
                 : Simulator::kRuntimeCall;
   entry =
       Simulator::RedirectExternalReference(entry, call_kind, argument_count);
 #endif
   if (is_leaf()) {
     ASSERT(argument_count == this->argument_count());
     ExternalLabel label(entry);
+    // Cache the stack pointer in a callee-saved register.
+    __ mov(R26, SP);
     __ BranchLink(&label, kNoPP);
+    __ mov(SP, R26);
   } else {
     // Argument count is not checked here, but in the runtime entry for a more
     // informative error message.
     __ LoadImmediate(R5, entry, kNoPP);
     __ LoadImmediate(R4, argument_count, kNoPP);
     __ BranchLink(&StubCode::CallToRuntimeLabel(), PP);
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64