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

Vladimir Kozlov vladimir.kozlov at
Tue Dec 18 14:24:43 PST 2012

But different alignment will require different encoding with compressed 
oops. How you solve that?


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
>>> <>
>>> Bug link at
>>> 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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