RFR: 8343531: Improve print_location for invalid heap pointers [v2]

[Aleksey Shipilev]

On Mon, 4 Nov 2024 10:46:02 GMT, Volker Simonis <simonis at openjdk.org> wrote:

>> Currently `BlockLocationPrinter<CollectedHeapT>::print_location()` checks for a pointer if it points into the heap and if that's true, it either prints it as an oop if `is_valid_obj()` is true or it tries to find the the start address of an oop for that pointer by calling `CollectedHeapT::heap()->block_start()`.
>> 
>> However, the `block_start()` functionality is not fully implemented for all GCs (e.g. the young generation of `ParallelScavengeHeap`) and for these cases `block_start()` returns NULL. Because of this NULL return value `os::print_location()` will finally qualify the corresponding pointer as pointing "into unknown readable memory" although we already know that it actually points into an invalid heap area.
>> 
>> In such cases, print at least that the pointer is pointing into an unknown part of the heap instead of just saying that it points into unknown memory. 
>> 
>> I've manually tested the new functionality in GDB.
>
> Volker Simonis has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Small refactoring based on tschatzl's review

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/21870#pullrequestreview-2413449596