RFR: 8365229: ARM32: c2i_no_clinit_check_entry assert failed after JDK-8364269 [v2]

[Aleksey Shipilev]

> 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:

  Offset -1 means nullptr

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26746/files
  - new: https://git.openjdk.org/jdk/pull/26746/files/5a994a75..9ad2cfb0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26746&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26746&range=00-01

  Stats: 13 lines in 2 files changed: 8 ins; 0 del; 5 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