RFR: 8330185: Potential uncaught unsafe memory copy exception

[Vladimir Kozlov]

On Fri, 12 Apr 2024 20:00:35 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

> Adding an `UnsafeCopyMemoryMark` in `generate_disjoint_copy_avx3_masked()` to protect against SIGBUS in `arraycopy_avx3_large()`.  I discovered this by code inspection, and the missing memory mark is inconsistent with all other generators.  I do not have a testcase to generate such an exception.  I think this may have been a copy/paste error by the original contributor as evidenced by the variable `ucme_exit_pc` having been set but never used.
> 
> I have not seen a VM crash that can be attributed to this, but adding the mark is the correct behavior for its prevention.

I will wait second review before sponsoring.

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PR Comment: https://git.openjdk.org/jdk/pull/18766#issuecomment-2052693606