RFR: JDK-8294902: Undefined Behavior in C2 regalloc with null references [v6]

[Kim Barrett]

On Fri, 2 Dec 2022 10:19:33 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> This patch fixes the remaining null pointer dereference bugs that I know of.
>> 
>> For the main bug, C2 was using a null reference to indicate an uninitialized `Node_List`. I replaced the null reference with a static sentinel.
>> 
>> I also turned on `-fsanitize=null` and found and fixed a bunch of other null pointer dereferences. With this,I have run a full bootstrap and tier1 tests with `-fsanitize=null` enabled.
>> 
>> I have checked that the code generated by GCC is not worse in any significant way, so I don't expect to see any performance regressions.
>> 
>> I'd like to enable `-fsanitize=null` in debug builds to prevent regressions in this area. What do you think?
>
> Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Feedback from reviewers

Regarding enabling `fsanitize=null` by default in debug builds, that may run afoul of incompatibilities between
sanitizers and `_FORTIFY_SOURCE`, which we already use in fastdebug builds.  See `FLAGS_SETUP_OPTIMIZATION`
in flags-cflags.m4, where `_FORTIFY_SOURCE` is setup unless ASan is enabled.

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PR: https://git.openjdk.org/jdk/pull/10920