Rejected AArch64 jdk8u backports

[Andrew Haley]

I've been going though AArch64 jdk8u backports.
The following backports should (probably) NOT be done in 8u; reasons follow.


8219006: AArch64: Register corruption in slow subtype check

Only affects debug builds; patch is fiddly and risky.

8219698: aarch64: SIGILL triggered when specifying unsupported hardware features

Only happens due to user error: the problem is between keyboard and chair.

8219993: AArch64: Compiled CI stubs are unsafely modified

This is a rather theoretical bug in that the AArch64 back end modifies
stubs in a way that IMO doesn't conform to the AArch64 memory
model. However, the fix is complicated and the problem has never
manifested in any test cases, so it's better to leave it as it is in
8u.

8222412: AARCH64: multiple instructions encoding issues

Big and intrusive, fixes no user-visible bugs, so not appropriate for
8u.

8229118: [TESTBUG] serviceability/sa/ClhsdbFindPC fails on AArch64

Serviceability test. Not important.

8232591: AArch64: Add missing match rules for smaddl, smsubl and smnegl

C2 enhancement. Might break things, small performance improvement,
hard to test, so not for 8u.

8233912: aarch64: minor improvements of atomic operations

Another rather theoretical patch that fixes no known bugs.

8234794: AArch64: runtime/memory/ReadFromNoaccessArea.java crashes
Summary: try to map CDS shared space at 4G aligned address on AArch64

Not applicable to 8u.

8235385: AArch64: Crash on aarch64 JDK due to long offset

This is a real bug but it requires a very contrived test case to
trigger it and the fix is complex. Probably not worth it.

8237512: AArch64: aarch64TestHook leaks a BufferBlob

Only gets triggered in debug builds. Not important for 8u.

8237524: AArch64: String.compareTo() may return incorrect result

Code being patched does not exist in 8u.

8239787: AArch64: String.indexOf may incorrectly handle empty strings

Likewise

8240353: AArch64: missing support for -XX:+ExtendedDTraceProbes in C1

Enhancement-only patch.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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