RFR: 8366145: G1: Help diagnose ubsan division by zero in computing pause time ratios (g1Analytics.cpp) [v2]

[Thomas Schatzl]

On Wed, 27 Aug 2025 16:26:53 GMT, Leo Korinth <lkorinth at openjdk.org> wrote:

>> This pull request is created to help diagnose the bug report https://bugs.openjdk.org/browse/JDK-8354430.
>> 
>> The problem is that we get a ubsan runtime error when dividing by zero. Ubsan is not normally running, so I will add an assert making it easier to catch the problem and printing the value of the two variables that when subtracted will create a zero; it will hopefully help with diagnosis.
>> 
>> Some comments: 
>> 1) the result of `most_recent_gc_end_time_sec()` will not change within the function, thus I will not clutter the code with a new variable, is that okay?
>> 2) I added two calls to `fabs` which are most probably not needed (ieee floating point rules seems to say that positive and negative zero equals). However I think my proposed code makes it clear that I have thought about it. 
>> 
>> I am now running tier1-3
>
> Leo Korinth has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - Merge branch 'master' into _8366145
>  - 8366145: Help diagnose ubsan failure

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26939#pullrequestreview-3163683368