RFR: 8277854: The upper bound of GCCardSizeInBytes should be limited to 512 for 32-bit platforms

[Hamlin Li]

On Fri, 26 Nov 2021 06:29:45 GMT, Jie Fu <jiefu at openjdk.org> wrote:

> Hi all,
> 
> runtime/CommandLine/OptionsValidation/TestOptionsWithRanges.java crashes on linux/x86_32 with `-XX:GCCardSizeInBytes=1024`.
> 
> This is because if`-XX:GCCardSizeInBytes=1024` then `BOTConstants::N_words` [1] would be 256.
> Then the guarantee [2] always fails due to _bot->offset_array(start_card), which is a u_char value, never equals to 256.
> 
> So for 32-bit platforms, the upper bound of `GCCardSizeInBytes` should be limited to 512.
> 
> Thanks.
> Best regards,
> Jie
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/shared/blockOffsetTable.cpp#L45
> [2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/g1/g1BlockOffsetTable.cpp#L186

Several initial comments:
 - Not sure if the lower bound should also be distinguished between 32 and 64. It's not because of crash, but as you're touching it, should we consider this?
 - Does a CSR needed?
 - A regression test would be helpful.

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PR: https://git.openjdk.java.net/jdk/pull/6569