RFR: 8316514: Better diagnostic header for VtableStub

[Tobias Hartmann]

On Tue, 19 Sep 2023 10:07:28 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Similar to [JDK-8316178](https://bugs.openjdk.org/browse/JDK-8316178), but for VtableStubs. JMH perfasm would like to know where the stub code ends.
> 
> Printout before this fix:
> 
> 
> Decoding VtableStub vtbl[5]@281473683415027
> --------------------------------------------------------------------------------
>   0x0000ffff9bf22320:   ldr     w16, [x1, #8]
>   0x0000ffff9bf22324:   movk    x16, #0x98, lsl #32
>   0x0000ffff9bf22328:   ldr     x12, [x16, #496]
>   0x0000ffff9bf2232c:   ldr     x8, [x12, #64]
>   0x0000ffff9bf22330:   br      x8
>   0x0000ffff9bf22334:   udf     #0
> 
> 
> Printout after this fix:
> 
> 
> --------------------------------------------------------------------------------
> Decoding VtableStub vtbl[5]@281473592893427 [0x0000ffff97f22320, 0x0000ffff97f22338] (24 bytes)
> --------------------------------------------------------------------------------
>   0x0000ffff97f22320:   ldr     w16, [x1, #8]
>   0x0000ffff97f22324:   eor     x16, x16, #0x3800000000
>   0x0000ffff97f22328:   ldr     x12, [x16, #496]
>   0x0000ffff97f2232c:   ldr     x8, [x12, #64]
>   0x0000ffff97f22330:   br      x8
>   0x0000ffff97f22334:   udf     #0

Looks good and trivial to me.

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

Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15816#pullrequestreview-1635362954