Getting ciObject from oop/jobject

[Krystal Mok]

Hi Nick,

All right, that explains everything. My take on this:

In HotSpot VM, the compiler threads shouldn't manipulate the Java object
graph; in other words, although the compilers have access to certain Java
objects through the Compiler Interface, it should only be "reading", but
not "writing" or creating new Java objects.

In your case, calling java_lang_StackTraceFrame::create() from compiler
code creates a new object, and that's probably not the right way.
You're trying to embed a pointer to a StackTraceFrame object in the
generated code, as a constant. You don't have to do that. It might work if
you embed the Method* (as a TypeMetadataPtr), and generate a runtime call
to java_lang_StackTraceFrame::create() with that pointer, instead of
calling it at compile time.

HTH,
Kris


On Fri, Aug 2, 2013 at 9:28 AM, Nick Williams <
nicholas+openjdk at nicholaswilliams.net> wrote:

> Well let me explain what I'm trying to do, and maybe someone can point me
> in the right direction.
>
> On the core-libs-dev mailing list, I proposed a public API replacement for
> the sun.reflect.Reflection#getCallerClass(int) of old and
> the sun.reflect.Reflection#getCallerClass() of now. The new class,
> java.lang.StackTraceFrame, has the following four methods that are relevant
> to this discussion:
>
> @CallerSensitive
> public native Class<?> getCallerClass();
> public native Class<?> getCallerClass(int);
> @CallerSensitive
> public native StackTraceFrame getCallerFrame();
> public native StackTraceFrame getCallerFrame(int);
>
> There is code in library_call.cpp that inlines
> Reflection.getCallerClass(), and I took advantage of that code to also
> inline StackTraceFrame.getCallerClass(). I also recreated (with changes
> necessary due to new way of doing things in library_call.cpp) the inline
> code for Reflection.getCallerClass(int) from the jdk7 source code. All of
> that works perfectly. Code is inlined as expected, and all is well.
>
> Now I want to inline getCallerFrame() and getCallerFrame(int) as well. If
> the Class<?> versions can be inlined, I see no reason that the
> StackTraceFrame versions can't be inlined, but that may be my first wrong
> assumption. If these methods aren't eligible for inlining for some reason,
> please let me know and I can move on.
>
> So the code that gets the Class<?> and sets it as an inline constant
> replacing the method call works like this (where m is a ciMethod*):
>
>           // Acquire method holder as java.lang.Class and push as constant.
>           ciInstanceKlass* caller_klass = m->holder();
>           ciInstance* caller_mirror = caller_klass->java_mirror();
>           set_result(makecon(TypeInstPtr::make(caller_mirror)));
>
> In javaClasses.cpp, I already have a method that can create a
> StackTraceFrame from a Method* (not ciMethod*), method version (int), and
> bci (int):
>
> oop java_lang_StackTraceFrame::create(Method* method, int version, int
> bci, TRAPS);
>
> I tried calling that to create the StackTraceFrame, but it appears I can't
> actually set it to the result. First I tried this:
>
>           // Acquire java.lang.StackTraceFrame and push as constant
>           Method* method = (Method*)m->constant_encoding();
>           oop stFrame = java_lang_StackTraceFrame::create(method,
> method->constants()->version(), caller_jvms->bci(), NULL);
>           set_result(makecon(TypeInstPtr::make(oop)));
>
> But this obviously didn't work because there is no TypeInstPtr::make()
> method that takes an oopDesc&. So I looked around trying to figure out how
> to convert an oop (or jobject, which I can get from an oop)  to a ciObject.
> I discovered that ciObject actually holds a jobject internally, so I
> figured surely this is possible. I found a few methods that appear to do
> it. ciObjectFactory has a ciObject* get(oop) method, but I can't figure out
> how to get the ciObjectFactory. ciEnv has a ciObject* get_object(oop)
> method which I tried to use, only to discover that it was private:
>
>           // Acquire java.lang.StackTraceFrame and push as constant
>           Method* method = (Method*)m->constant_encoding();
>           oop stFrame = java_lang_StackTraceFrame::create(method,
> method->constants()->version(), caller_jvms->bci(), NULL);
>           ciObject* stfObject = ciEnv::current()->get_object(stFrame);
>           set_result(makecon(TypeInstPtr::make(stfObject)));
>
> So that obviously doesn't work either. I'll admit, I'm a little out of my
> league here. I was pretty confident working in javaClasses.hpp/cpp and
> jvm.h/cpp, but this inlining/compiler stuff is pretty over my head.
> Hopefully one of the knowledgeable people on this list can help me out with
> this. I want my code to perform as well as possible and also be
> stable--more likely to get accepted that way. :-)
>
> Thanks,
>
> Nick
>
> On Aug 1, 2013, at 8:16 AM, Krystal Mok wrote:
>
> Hi Nick,
>
> This topic is related to HotSpot Server Compiler instead of the Java core
> library, so I'm cc'ing this email to hotspot-compiler-dev and dropping
> core-libs-dev.
>
> As you already know, HotSpot compilers are shielded from VM runtime
> implementation details via the Compiler Interface (CI). That's why you
> shouldn't be getting raw oops in C2 code.
>
> Where are you getting the oopInstance from? If it can be found from some
> known "roots", e.g. "well-known classes", fields of "well-known classes",
> or the holder class of the method to be compiled, etc., then it's already
> available through CI.
>
> - Kris
>
>
> On Thu, Aug 1, 2013 at 3:17 AM, Nick Williams <
> nicholas+openjdk at nicholaswilliams.net> wrote:
>
>> In native code (library_call.cpp), if I have an oop (which I can convert
>> to a jobject if need be), how do I get a ciObject? I see that ciEnv has a
>> ciObject* get_object(oop) method, but it's private. And ciObjectFactory has
>> a ciObject* get(oop) method, but I can't figure out how to get the
>> ciObjectFactory instance.
>>
>> I know that ciObject keeps a jobject internally, and I know that ciObject
>> has a ciObject(oop) constructor, but it's protected (for good reason).
>>
>> If it helps, I'm trying to inline a method and need to
>> set_result(makecon(TypeInstPtr::make(oopInstance))). I may be going down
>> the wrong path.
>>
>> Thanks in advance for any help,
>>
>> Nick
>
>
>
>
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