RFR: 8343140: JfrJavaSupport uses the wrong accessors for sub-int fields

[Aleksey Shipilev]

On Thu, 7 Nov 2024 12:57:20 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

> This test fixes the accessor used by `read_boolean_field` to access boolean fields of the `jdk.jfr.internal.dcmd.Argument` record. It also fixes the read accessors for `short` and `char` types, and marks the write accessors for `boolean`, `short` and `char` as unimplemented.
> 
> The existing accessor reads the boolean field as int. This results in unaligned access, and probably reads incorrect value on big-endian CPUs.
> 
> No new tests. I'm sure a test would be useful, but I have no idea how to write one. Existing tier1-3 tests continue to pass.

Ouch, good find.

src/hotspot/share/jfr/jni/jfrJavaSupport.cpp line 347:

> 345:     case T_SHORT:
> 346:       Unimplemented();
> 347:       break;

Why not implement these, while we are at it?

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PR Review: https://git.openjdk.org/jdk/pull/21952#pullrequestreview-2421678492
PR Review Comment: https://git.openjdk.org/jdk/pull/21952#discussion_r1833081878