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

[Thomas Schatzl]

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

Thanks for spotting this - that slipped past our testing (we do not do much 32 bit testing).

>>  Does a CSR needed?
>
> Maybe not since no VM flags are added or removed and jdk18 hasn't been released yet.
> But I'm not sure.

I will talk to the CSR team whether there needs to be an amendment to the CSR for 32 bit platforms. please do not integrate before this has been handled.

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