Move some isolate state setup from C++ code to JumpToExceptionHandler stub

runtime/vm/stub_code_arm.cc

 // Copyright (c) 2013, 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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 1667 matching lines @@
   __ Ret();
 }
 
 
 // Jump to the exception or error handler.
 // LR: return address.
 // R0: program_counter.
 // R1: stack_pointer.
 // R2: frame_pointer.
 // R3: error object.
-// SP: address of stacktrace object.
+// SP + 0: address of stacktrace object.
+// SP + 4: isolate
 // Does not return.
 void StubCode::GenerateJumpToExceptionHandlerStub(Assembler* assembler) {
   ASSERT(kExceptionObjectReg == R0);
   ASSERT(kStackTraceObjectReg == R1);
   __ mov(IP, Operand(R1));  // Stack pointer.
   __ mov(LR, Operand(R0));  // Program counter.
   __ mov(R0, Operand(R3));  // Exception object.
   __ ldr(R1, Address(SP, 0));  // StackTrace object.
+  __ ldr(CTX, Address(SP, 4));  // Isolate.

[regis, 2014/07/14 20:00:34]

Are you sure it is OK to trash the CTX register? I guess it is, but to be safe,
you could use R3.

[Cutch, 2014/07/14 21:32:07]

Done.

   __ mov(FP, Operand(R2));  // Frame_pointer.
   __ mov(SP, Operand(IP));  // Stack pointer.
+  // Set the tag.
+  __ LoadImmediate(R2, VMTag::kScriptTagId);
+  __ StoreToOffset(kWord, R2, CTX, Isolate::vm_tag_offset());
+  // Clear top exit frame.
+  __ LoadImmediate(R2, 0);
+  __ StoreToOffset(kWord, R2, CTX, Isolate::top_exit_frame_info_offset());
   __ bx(LR);  // Jump to the exception handler code.
 }
 
 
 // Calls to the runtime to optimize the given function.
 // R6: function to be reoptimized.
 // R4: argument descriptor (preserved).
 void StubCode::GenerateOptimizeFunctionStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ Push(R4);
@@ skipping 128 matching lines @@
   const Register right = R0;
   __ ldr(left, Address(SP, 1 * kWordSize));
   __ ldr(right, Address(SP, 0 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM