RFR: 8334866: Improve Speed of ElfDecoder source search [v4]

[Kim Barrett]

On Tue, 21 Oct 2025 16:31:48 GMT, Kerem Kat <krk at openjdk.org> wrote:

>> Right now, looking up source file and line number info is slow because we do a full linear scan of the `.debug_aranges` section for every single call. This can be a major bottleneck on large binaries, especially during frequent native stack walking, e.g. while writing an hs_err.
>> 
>> This change fixes that by caching the address ranges on the first lookup, and keeping it in memory for the lifetime of the `DwarfFile` object.
>> 
>> All subsequent lookups on that object now use a binary search instead of the slow linear scan. If caching fails for any reason, it just falls back to the old method.
>
> Kerem Kat has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'master' into elfdecoder-JDK-8334866
>  - Merge remote-tracking branch 'upstream/master' into elfdecoder-JDK-8334866
>  - Merge remote-tracking branch 'upstream/master' into elfdecoder-JDK-8334866
>  - 8334866: Cache debug_aranges for faster address lookups

src/hotspot/share/utilities/elfFile.hpp line 551:

> 549:     void sort() {
> 550:       qsort(_entries, _count, sizeof(ArangesEntry), DwarfFile::ArangesCache::compare_aranges_entries);
> 551:     }

[drive-by comment] Use of qsort is questionable.  See https://bugs.openjdk.org/browse/JDK-8248137

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PR Review Comment: https://git.openjdk.org/jdk/pull/27337#discussion_r2452029592