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

[Ioi Lam]

On Thu, 1 Oct 2020 22:40:46 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

> CDS aligns pointers and sizes to BytesPerWord. On 64-bit, BytesPerWord = 8. On 32-bit, BytesPerWord = 4.
> 
> To make the alignment consistent between 64- and 32-bit platforms, this patch changes the alignment value to 8.
> 
> Testing: tiers 1 - 4
>                built linux-x86-debug.

Marked as reviewed by iklam (Reviewer).

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;

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