RFR: 8365229: ARM32: c2i_no_clinit_check_entry assert failed after JDK-8364269 [v4]
Aleksey Shipilev
shade at openjdk.org
Wed Aug 13 11:16:59 UTC 2025
> When recording adapter entries, we record _offsets_, not the actual addresses:
>
>
> entry_offset[3] = handler->get_c2i_no_clinit_check_entry() - i2c_entry;
>
>
> Every platform except ARM32 and Zero have all these entries set up, so offset are always sane. But those two platforms set up `nullptr` as `c2i_no_clinit_check_entry()`, because clinit barriers are unimplemented. So the new assert added in [JDK-8364269](https://bugs.openjdk.org/browse/JDK-8364269) fails encountering effectively `nullptr - i2c_entry` "garbage".
>
> This PR is the second least horrible (IMO) fix for this: relaxing assert by checking that "out of range" values are actually wrapping around back to `0`/`nullptr`. Had to do it in unsigned ints to avoid UB. For the affected platforms, we do not actually access this problematic/garbage entry offset, since we are always checking if clinit barriers are enabled. So the assert is the only place where it matters.
>
> The least horrible solution would be storing the actual `address`-es instead of `int` offsets. But that likely has footprint implications.
>
> Additional testing:
> - [x] Linux x86_64 server fastdebug, `runtime/cds` still works
> - [x] Linux ARM32 server fastdebug, `java -version` now works
Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
Handling Zero crash as well
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/26746/files
- new: https://git.openjdk.org/jdk/pull/26746/files/7c33cc5e..aa62b27f
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=26746&range=03
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=26746&range=02-03
Stats: 7 lines in 2 files changed: 2 ins; 1 del; 4 mod
Patch: https://git.openjdk.org/jdk/pull/26746.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/26746/head:pull/26746
PR: https://git.openjdk.org/jdk/pull/26746
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