RFR: 8294314: Minimize disabled warnings in hotspot [v2]

[Magnus Ihse Bursie]

On Sat, 24 Sep 2022 03:33:34 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Magnus Ihse Bursie has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - ppc64 triggers shift-negative-value on gcc :-(
>>  - s390 triggers shift-negative-value on gcc :-(
>
> There used to be more comments around the warning disables. The Windows ones
> had comments that gave titles to the numeric codes. And I think there were
> some comments that discussed why a warning was disabled rather than fixing
> code. I don't know when that all disappeared, but it was quite a while ago,
> and I still miss that commentary.

@kimbarrett That must have been in the old hotspot build system then. 

We are now nearing a point were we have so few disabled warnings that it makes sense to  write down some rationale for those we have left, at least those which are globally (I assume you mean "for hotspot" with "globally" :-)) disabled. 

There is also a list of truly globally disabled warnings (for all native code in the JDK, not only hotspot). These should need some reviewing as well, and if we agree to keep them globally disabled, a rationale can be provided.

If the documentation tends to be to long and rambling, we might need to put it elsewhere than as comments in the makefiles though, perhaps as a separate document.

I can make a summary of the warnings that are no longer globally disabled with this fix, so you can check if some of them should be (even if they are not triggering anything right now).

Also note that I ran into a lot of trouble with the cross-compilation on GHA, so I'll have to either replicate those locally, or fight a bit with GHA to get progress more than one file at a time. In any case, it will take a while for me to sort out.

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PR: https://git.openjdk.org/jdk/pull/10414