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From Gregory Shimansky <gshiman...@gmail.com>
Subject Re: [DRLVM] (JIRA 1580) write barrier implementation for JET
Date Wed, 27 Sep 2006 22:27:29 GMT
On Wednesday 27 September 2006 14:20 Egor Pasko wrote:
> On the 0x1F1 day of Apache Harmony Xiao-Feng Li wrote:
> > Thanks. Yes, this is supposed to be review by JIT person. On the other
> > hand, if JIT person has better solution, GCv5 would like to use.
> > Anyway we hope write barrier is to be functioning in the DRLVM soon.
>
> As a JIT-oriented guy, I looked through the patch. Looks good. The
> write barrier does NOT push an M2N frame before invoking
> gc_heap_slot_write_ref(), but it's OK since there will be no stack
> unwinding from here.

I want to make sure that there are going to be no JVMTI events sent inside of 
gc_heap_slot_write_ref. Otherwise M2N frame is necessary to allow stack 
iterator to work in case a JVMTI agent calls something like GetStackTrace.

Also can a hardware exception occur as a result of this helper call?

Just a note. Patch uses tabs and DOS EOLs. Can we use spaces and unix line 
endings instead?

> I am curious about the switch
> VM_Global_State::loader_env->use_lil_stubs. Does everything work in
> both true and false? What do we need this switch for? Doesn't it
> induce unnecessary complication/duplication?
>
> > On 9/27/06, Weldon Washburn <weldonwjw@gmail.com> wrote:
> > > It would probably be best if a JIT person committed this patch.  Maybe
> > > Stephan Mishura?
> > >
> > > If its not committed soon, bug me and I will do it.
> > >
> > > On 9/26/06, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> > > > Hi, the patch attached in JIRA 1580 (submitted by YuNan) is a write
> > > > barrier implementation for JET that GCv5 is going to use (it doesn't
> > > > impact anything else). It would be great if some commiter can help to
> > > > review and commit it. Thanks. -xiaofeng
> > > >
> > > > http://issues.apache.org/jira/browse/HARMONY-1580?page=all
> > > >
> > > > The patch is against revision revision 442796.
> > > >
> > > > Repeat the desciption of the patch:
> > > > "Attached patch is an implementation of write barrier for JET
> > > > compiler of DRLVM. The patch lets JET to call
> > > > "gc_requires_barriers()" of GC to determine if it needs to insert the
> > > > write barrier code into the jitted code, so it doesn't impact current
> > > > DRLVM/GC at all. It calls gc_heap_slot_write_ref( ) of GC module,
> > > > which takes three parameters. The signature is "void
> > > > gc_heap_slot_write_ref (Managed_Object_Handle
> > > > p_obj_holding_ref,Managed_Object_Handle *p_slot,
> > > > Managed_Object_Handle p_target)".
> > > >
> > > > The patch is based on revision 442796. We hope it can be committed to
> > > > Harmony soon because GCv5 will be depending on it. We don't use
> > > > existing getaddress__gc_write_barrier_fastcall () in DRLVM because it
> > > > only remembers object rather than the slot, and the name is not
> > > > descriptive. But we may use it later. Thanks."

-- 
Gregory Shimansky, Intel Middleware Products Division

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