hg: valhalla/valhalla/hotspot: Fix and cleanup in vwithfield

Frederic Parain frederic.parain at oracle.com
Wed Jun 7 21:16:36 UTC 2017


Karen,

The integer returned is not the size of the new value type, it’s a stack
adjustment value.

The vwithfield runtime entry returns a new value type in thread->vm_result
and an integer which is used by the assembly code to adjust the stack
pointer (the vwithfield bytecode must consume the new field value and the
original value type passed on the stack before pushing the new value).
We are doing this because we cannot manipulate the expression stack from
the runtime and the assembly code doesn’t know the size of
the new field value (one slot or two slot depending on the field type).

The bug was that the stack adjustment returned was missing the size of
the original value type passed on the stack, leading to a “shift” of operands
on the expression stack because the original value type was never popped.
This issue caused some GC issues (because of the shift, there was a
mismatch between the oopmap computed and the real location of references),
and could eventually caused some stack overflow issues.

Fred


> On Jun 7, 2017, at 17:04, Karen Kinnear <karen.kinnear at oracle.com> wrote:
> 
> Frederic,
> 
> Looks good. Thank you for the cleanup.
> 
> One question please - why do you add type2size(T_VALUETYPE) * stackElementSize
> when you return the size of the new value type result?
> 
> thanks,
> Karen
> 
>> On Jun 7, 2017, at 3:41 PM, Frederic Parain <frederic.parain at oracle.com> wrote:
>> 
>> Fixing a bug in vwithfield leading to buggy stack management.
>> Thanks to Mr Simms for having spotted and identify the issue.
>> I took the opportunity to do a clean up of the vwithfield method,
>> removing raw pointer arithmetic on the expression stack, using
>> the frame API instead.
>> 
>> Fred
>> 
>> 
>>> On Jun 7, 2017, at 15:39, frederic.parain at oracle.com wrote:
>>> 
>>> Changeset: b03e14ea3e9b
>>> Author:    fparain
>>> Date:      2017-06-07 15:38 -0400
>>> URL:       http://hg.openjdk.java.net/valhalla/valhalla/hotspot/rev/b03e14ea3e9b
>>> 
>>> Fix and cleanup in vwithfield
>>> 
>>> ! src/share/vm/interpreter/interpreterRuntime.cpp
>>> 
>> 
> 



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