RFR: 8334866: Improve Speed of ElfDecoder source search [v7]

[Christian Hagedorn]

On Wed, 29 Oct 2025 15:16:39 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 19 additional commits since the last revision:
> 
>  - fix space
>  - Address comments and better guess the initial cache size
>  - Merge branch 'master' into elfdecoder-JDK-8334866
>  - Fix comments, delete copy ctor
>  - Merge branch 'master' into elfdecoder-JDK-8334866
>  - fix DWARF_LOG_INFO
>  - Comment on ArangesCache
>  - Fix secondary sort order and comment
>  - Remove move ctor of ArangesCache
>  - Clarify when we can fallback to linear scan, which doesn't seem to allocate on the heap
>  - ... and 9 more: https://git.openjdk.org/jdk/compare/e523131d...9814a3ff

Thanks a lot for the update and showing some more benchmark results, looks good!

src/hotspot/share/utilities/elfFile.hpp line 540:

> 538:       FAILED,
> 539: 
> 540:       // Cache is usable, no need to fallback to linear scan.

Suggestion:

      // Cache is usable, no need to fall back to linear scan.

-------------

Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27337#pullrequestreview-3399078277
PR Review Comment: https://git.openjdk.org/jdk/pull/27337#discussion_r2477696960