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

Coleen Phillimore coleen.phillimore at
Thu Dec 20 11:43:59 PST 2012

I think this looks good.  The fail_continue should just stop using the 
shared archive if you have -Xshare:auto.  I believe it only prints a 
message and dies if you have -Xshare:on.   The default for server is 
-Xshare:off right now but someday it might be -Xshare:auto if we get the 
performance problems resolved. (-XX:+RewriteBytecodes is off for CDS and 
affects server performance)


On 12/20/2012 01:53 PM, harold seigel wrote:
> 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: 
> <>
> 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
>>>>> <>
>>>>> 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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