RFR: 8339242: Fix overflow issues in AdlArena [v3]

[Casper Norrbin]

On Tue, 3 Sep 2024 13:46:57 GMT, Casper Norrbin <duke at openjdk.org> wrote:

>> Hi everyone,
>> 
>> This PR addresses an issue in `adlArena` where some allocations lack checks for overflow. This could potentially result in successful allocations when called with unrealistic values.
>> 
>> The fix includes:
>> 
>> - Adding assertions to check for potential overflow.
>> - Reordering some operations to guard against overflow.
>
> Casper Norrbin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   saturated pointer adds + size asserts

Here are my thoughts after looking through this again and reading your comments.

I agree that blindly reshuffling parameters to prevent overflow may not be the best solution. I think using something like `pointer_delta` strikes a good balance.  Using a saturated add feels to me like checking for overflow, just with extra steps.

I also believe that asserting for ”reasonable” arena allocation sizes may be out of scope of this PR. The initial purpose was to fix potential overflow issues in the adlc arena, and has already expanded into the regular arena. These asserts also causes test failures, so even more changes would be required if added. It may be better to create a separate issue for generally improving arena allocation safety.

With the overflow checks in place, Kim’s refactor is a bit cleaner and more readable than the modified original, so I’ve opted to implement that.


Please let me know any further comments or suggestions

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PR Comment: https://git.openjdk.org/jdk/pull/20774#issuecomment-2331836199