RFR: 8365047: Remove exception handler stub code in C2 [v5]

[Martin Doerr]

On Fri, 26 Sep 2025 12:16:24 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code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.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 incrementally with two additional commits since the last revision:
> 
>  - Address review comments
>  - The patch is contributed by @TheRealMDoerr

Thank you so much for doing the work for all platforms! It looks correct to me.
Should we rename `entry_point` to `entry_offset` in the deopt handlers to emphasize that it's an offset and not a pointer?

src/hotspot/share/ci/ciEnv.cpp line 3:

> 1: /*
> 2:  * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
> 3:  * Copyright 2025 Arm Limited and/or its affiliates.

This Copyright addition looks a bit disproportionate. I wouldn't call the assertion adaptation a major contribution to this file.

src/hotspot/share/code/nmethod.cpp line 3:

> 1: /*
> 2:  * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
> 3:  * Copyright 2025 Arm Limited and/or its affiliates.

Still questionable, here. Do we have clear guidelines?

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PR Review: https://git.openjdk.org/jdk/pull/26678#pullrequestreview-3272133194
PR Review Comment: https://git.openjdk.org/jdk/pull/26678#discussion_r2382338233
PR Review Comment: https://git.openjdk.org/jdk/pull/26678#discussion_r2382339599