RFR: 8224509: Incorrect alignment in CDS related allocation code on 32-bit platforms [v2]

[Calvin Cheung]

On Fri, 2 Oct 2020 05:03:45 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> src/hotspot/share/memory/archiveUtils.hpp line 33:
>> 
>>> 31: #include "utilities/bitMap.hpp"
>>> 32:
>>> 33: #define SharedSpaceObjectAlignment      8
>> 
>> I think we can use a `const int` instead of `#define`. Also, some comments will be helpful. Maybe:
>> 
>> // Metaspace::allocate() requires that all blocks must be aligned with KlassAlignmentInBytes.
>> // We enforce the same alignment rule in blocks allocated from the shared space.
>> const int SharedSpaceObjectAlignment = KlassAlignmentInBytes;
>
> +1 to making the dependency on KlassAlignment explicit. Please do not hide any dependencies on Klass alignment behind
> literals (I am currently experimenting with increasing class space allocation alignment to increase the range of
> zero-based Klass* encoding)

Thanks @iklam and @tstuefe for the review.
I've made the change in webrev 01.

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PR: https://git.openjdk.java.net/jdk/pull/476