RFR(M): 8166317: InterpreterCodeSize should be computed

[Volker Simonis]

Hi,

I've decided to split the fix for the 'CodeHeap::contains_blob()'
problem into its own issue "8187091: ReturnBlobToWrongHeapTest fails
because of problems in CodeHeap::contains_blob()"
(https://bugs.openjdk.java.net/browse/JDK-8187091) and started a new
review thread for discussing it at:
http://mail.openjdk.java.net/pipermail/hotspot-dev/2017-September/028206.html

So please lets keep this thread for discussing the interpreter code
size issue only. I've prepared a new version of the webrev which is
the same as the first one with the only difference that the change to
'CodeHeap::contains_blob()' has been removed:

http://cr.openjdk.java.net/~simonis/webrevs/2017/8166317.v1/

Thanks,
Volker


On Thu, Aug 31, 2017 at 6:35 PM, Volker Simonis
<volker.simonis at gmail.com> wrote:
> On Thu, Aug 31, 2017 at 6:05 PM, Vladimir Kozlov
> <vladimir.kozlov at oracle.com> wrote:
>> Very good change. Thank you, Volker.
>>
>> About contains_blob(). The problem is that AOTCompiledMethod allocated in
>> CHeap and not in aot code section (which is RO):
>>
>> http://hg.openjdk.java.net/jdk10/hs/hotspot/file/8acd232fb52a/src/share/vm/aot/aotCompiledMethod.hpp#l124
>>
>> It is allocated in CHeap after AOT library is loaded. Its code_begin()
>> points to AOT code section but AOTCompiledMethod* points outside it (to
>> normal malloced space) so you can't use (char*)blob address.
>>
>
> Thanks for the explanation - now I got it.
>
>> There are 2 ways to fix it, I think.
>> One is to add new field to CodeBlobLayout and set it to blob* address for
>> normal CodeCache blobs and to code_begin for AOT code.
>> Second is to use contains(blob->code_end() - 1) assuming that AOT code is
>> never zero.
>>
>
> I'll give it a try tomorrow and will send out a new webrev.
>
> Regards,
> Volker
>
>> Thanks,
>> Vladimir
>>
>>
>> On 8/31/17 5:43 AM, Volker Simonis wrote:
>>>
>>> On Thu, Aug 31, 2017 at 12:14 PM, Claes Redestad
>>> <claes.redestad at oracle.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2017-08-31 08:54, Volker Simonis wrote:
>>>>>
>>>>>
>>>>> While working on this, I found another problem which is related to the
>>>>> fix of JDK-8183573 and leads to crashes when executing the JTreg test
>>>>> compiler/codecache/stress/ReturnBlobToWrongHeapTest.java.
>>>>>
>>>>> The problem is that JDK-8183573 replaced
>>>>>
>>>>>     virtual bool contains_blob(const CodeBlob* blob) const { return
>>>>> low_boundary() <= (char*) blob && (char*) blob < high(); }
>>>>>
>>>>> by:
>>>>>
>>>>>     bool contains_blob(const CodeBlob* blob) const { return
>>>>> contains(blob->code_begin()); }
>>>>>
>>>>> But that my be wrong in the corner case where the size of the
>>>>> CodeBlob's payload is zero (i.e. the CodeBlob consists only of the
>>>>> 'header' - i.e. the C++ object itself) because in that case
>>>>> CodeBlob::code_begin() points right behind the CodeBlob's header which
>>>>> is a memory location which doesn't belong to the CodeBlob anymore.
>>>>
>>>>
>>>>
>>>> I recall this change was somehow necessary to allow merging
>>>> AOTCodeHeap::contains_blob and CodeHead::contains_blob into
>>>> one devirtualized method, so you need to ensure all AOT tests
>>>> pass with this change (on linux-x64).
>>>>
>>>
>>> All of hotspot/test/aot and hotspot/test/jvmci executed and passed
>>> successful. Are there any other tests I should check?
>>>
>>> That said, it is a little hard to follow the stages of your change. It
>>> seems like
>>> http://cr.openjdk.java.net/~redestad/scratch/codeheap_contains.00/
>>> was reviewed [1] but then finally the slightly changed version from
>>> http://cr.openjdk.java.net/~redestad/scratch/codeheap_contains.01/ was
>>> checked in and linked to the bug report.
>>>
>>> The first, reviewed version of the change still had a correct version
>>> of 'CodeHeap::contains_blob(const CodeBlob* blob)' while the second,
>>> checked in version has the faulty version of that method.
>>>
>>> I don't know why you finally did that change to 'contains_blob()' but
>>> I don't see any reason why we shouldn't be able to directly use the
>>> blob's address for inclusion checking. From what I understand, it
>>> should ALWAYS be contained in the corresponding CodeHeap so no reason
>>> to mess with 'CodeBlob::code_begin()'.
>>>
>>> Please let me know if I'm missing something.
>>>
>>> [1]
>>> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2017-July/026624.html
>>>
>>>> I can't help to wonder if we'd not be better served by disallowing
>>>> zero-sized payloads. Is this something that can ever actually
>>>> happen except by abuse of the white box API?
>>>>
>>>
>>> The corresponding test (ReturnBlobToWrongHeapTest.java) specifically
>>> wants to allocate "segment sized" blocks which is most easily achieved
>>> by allocation zero-sized CodeBlobs. And I think there's nothing wrong
>>> about it if we handle the inclusion tests correctly.
>>>
>>> Thank you and best regards,
>>> Volker
>>>
>>>> /Claes