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

[Aleksey Shipilev]

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

src/hotspot/share/opto/postaloc.cpp line 259:

> 257:   if (!can_change_regs) {
> 258:     return blk_adjust;          // Only check stupid copies!
> 259:   }

Style nit here and in other places: weren't these blocks separated by newline before?

src/hotspot/share/utilities/globalDefinitions_gcc.hpp line 155:

> 153:   char* c = (char*)(void*)&dummyObj->field;     \
> 154:   return (size_t)(c - space);                   \
> 155: }()

I am very surprised this does not produce any warnings! Let me test this on different GCCs...

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