Add instrumentation in the TemplateInterpreter

[Khanh Nguyen]

Hello,

I want to add instrumentation to monitor all reads and writes in the
TemplateInterpreter, I think I got the correct place for it in
/cpu/x86/vm/templateTable_x86_64.cpp. Can someone please tell me if I'm
doing it right?

For writes:
static void do_oop_store(InterpreterMacroAssembler* _masm,
                         Address obj,
                         Register val,
                         BarrierSet::Name barrier,
                         bool precise) {
[...]
 case BarrierSet::CardTableModRef:
  case BarrierSet::CardTableExtension:
      {
        if (val == noreg) {
          __ store_heap_oop_null(obj);
        } else {
          __ store_heap_oop(obj, val);

 /*mycodeA*/  __ movptr(c_rarg1, obj.base()); // save this value otherwise
it will be changed?

          // flatten object address if needed
          if (!precise || (obj.index() == noreg && obj.disp() == 0)) {
            __ store_check(obj.base());
 /*mycodeB*/ __ call_VM(noreg, //void
                       CAST_FROM_FN_PTR(address,
                                        InterpreterRuntime::write_helper),
                       c_rarg1,  // obj
                       c_rarg1, // field address because store check is
called on field address
                       val);
          } else {
            __ leaq(rdx, obj);
            __ store_check(rdx);
 /*mycodeC*/ __ call_VM(noreg, //void
                         CAST_FROM_FN_PTR(address,
                                          InterpreterRuntime::write_helper),
                         c_rarg1,  // obj
                         rdx, // field address, because store check is
called on field address
                         val);
        }
      }
      break;

For reads:
case Bytecodes::_fast_agetfield:
    __ load_heap_oop(rax, field);

/*mycodeD*/     __ call_VM(noreg,
               CAST_FROM_FN_PTR(address,
                                InterpreterRuntime::read_barrier_helper),
               rax);

__ verify_oop(rax);
    break;

My questions are:

1) I thought this represents a putfield a.f=b where a.f is represented by
the parameter obj of type Address. b is obvious the parameter val of type
Register. Especially in obj there are fields: base, index and disp. But as
I run this, looks like obj is actually the field address. (the case mycodeB)
I haven't found a test case that can trigger the case mycodeC to see the
behavior (i.e., rdx might get destroyed and I got random value back or
c_rarg1 is the obj address and rdx is field address)

2) Before this, I tried to insert the same __ call_VM in fast_aputfield
before do_oop_store but it results in JVM crash. I don't understand the
reason why. What I did in the call is just print the parameters. I did see
the values printed (only the 1st time it goes to the method) but then the
VM crashed. I thought __ call_VM will preserve all registers's value and
restore properly when comes back. My instrumentation has no side effect, I
just observe and record the values (actually just printing the values to
test).

3) Is it strictly required to have the line /*mycodeA*/ I tried to, in
mycodeB line, pass obj.base() twice and it got build errors for "smashed
args"?

I greatly appreciate your time,

Best,

Khanh Nguyen