Request for review 8005075: CDS archive with one alignment causes crash when run with different alignment

[harold seigel]

Hi,

Based on Vladimir's comments, I changed the code to require that both 
alignments need to be the same.  Here's an example of the modified 
diagnostic:

    The shared archive file's ObjectAlignmentInBytes of 16 does not
    equal the current ObjectAlignmentInBytes of 8.

Please review this latest change at: 
http://cr.openjdk.java.net/~hseigel/bug_8005076_3/ 
<http://cr.openjdk.java.net/%7Ehseigel/bug_8005076_3/>

Thank you,
Harold


On 12/18/2012 5:24 PM, Vladimir Kozlov wrote:
> But different alignment will require different encoding with 
> compressed oops. How you solve that?
>
> Thanks,
> Vladimir
>
> On 12/18/12 1:34 PM, harold seigel wrote:
>> Hi Vladimir,
>>
>> A bigger original alignment is okay because alignment values must be
>> powers of 2.  This means that bigger alignments will always be multiples
>> of smaller alignments.  So, a bigger aligned object will also meet the
>> requirements of a smaller alignment.  For example, if the bigger
>> alignment is 32 then the smaller alignment must be either 8 or 16.  And,
>> a 32 byte aligned object is also 8 and 16 byte aligned.
>>
>> Harold
>>
>> On 12/18/2012 3:01 PM, Vladimir Kozlov wrote:
>>> Recording ObjectAlignmentInBytes in CDS is good. Thank you for doing 
>>> it.
>>> My question is why bigger original alignment is fine? I thought CDS
>>> works only when it is exactly the same.
>>>
>>> Thanks,
>>> Vladimir
>>>
>>> On 12/17/12 7:23 AM, harold seigel wrote:
>>>> Please review the following change to fix bug 8005075.
>>>>
>>>> Summary:  This change prevents a crash when a CDS archive is created
>>>> with a value for -XX:+ObjectAlignmentInBytes that is smaller than the
>>>> ObjectAlignmentInBytes value used when running with -Xshare:on. 
>>>> This fix
>>>> stores the ObjectAlignmentInBytes in the CDS archive so that when the
>>>> archive is read, hotspot can compare the archive's alignment with the
>>>> current alignment and issue the following diagnostic if the archive's
>>>> alignment is too small:
>>>>
>>>>     An error has occurred while processing the shared archive file.
>>>>     The shared archive file was created with a smaller Object 
>>>> Alignment
>>>>     value.
>>>>
>>>> This webrev also cleans up some text in globals.hpp and fixes a small
>>>> problem with -XX:SharedReadOnlySize.  The existing code was always
>>>> setting SharedReadOnlySize to 14M regardless of what was requested.
>>>> This prevented users from being able to expand the CDS archive's
>>>> SharedReadOnly section.
>>>>
>>>> Open webrev at http://cr.openjdk.java.net/~hseigel/bug_8005076/
>>>> <http://cr.openjdk.java.net/%7Ehseigel/bug_8005076/>
>>>>
>>>> Bug link at http://bugs.sun.com/view_bug.do?bug_id=8005076
>>>>
>>>> The changes were tested with JCK, JPRT, JTREG, and UTE tests, and with
>>>> hand-run tests using different ObjectAlignmentInBytes values.
>>>>
>>>> Thanks, Harold
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