RFR: 8365047: Remove exception handler stub code in C2 [v7]

[Martin Doerr]

On Mon, 13 Oct 2025 11:45:02 GMT, Ruben <duke at openjdk.org> wrote:

>> The C2 exception handler stub code is only a trampoline to the generated exception handler blob. This change removes the extra step on the way to the generated blob.
>> 
>> According to some comments in the source code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.
>
> Ruben has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:
> 
>  - Merge from the main branch
>  - Address review comments
>  - Address review comments
>  - Address review comments
>  - The patch is contributed by @TheRealMDoerr
>  - Offset the deoptimization handler entry point
>    
>    Change-Id: I596317ec6a364b341e4642636fa5cf08f87ed722
>  - Revert "Ensure stub code is not adjacent to a call"
>  - Ensure stub code is not adjacent to a call
>  - Address review comments
>  - 8365047: Remove exception handler stub code in C2
>    
>    The C2 exception handler stub code is only a trampoline to the
>    generated exception handler blob. This change removes the extra
>    step on the way to the generated blob.
>    
>    According to some comments in the source code, the exception handler
>    stub code used to be patched upon deoptimization, however presumably
>    these comments are outdated as the patching upon deoptimization happens
>    for post-call NOPs only.

Btw. the disassembled instructions above are coming from https://github.com/openjdk/jdk/pull/27530 which we currently use in our test environment. Reviews would help to get it integrated.

0x0000f7cf03c5fff8:   62 74 ef 17 ff ff ff 17 
--------------------------------------------------------------------------------
  0x0000f7cf03c5fff8:   b	0x0000f7cf0383d180
  0x0000f7cf03c5fffc:   b	0x0000f7cf03c5fff8

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

PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3432573526