RFR: 8304888: Add dedicated VMProps for linker and fallback linker [v3]

[Jorn Vernee]

On Fri, 28 Apr 2023 12:59:26 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch adds a dedicated jtreg property to check which CABI is being used by the JDK, which can be used both to check whether the foreign linker is supported, and whether the fallback linker is being used. (and, possibly it can also be use to check for a particular ABI in case we want to add ABI specific tests).
>> 
>> Checking whether the foreign linker is supported currently requires using an unwieldy expression that checks if we are running on a platform that has a foreign linker port. Checking for the fallback linker currently uses `vm.flavor != "zero"` which is not always correct, since the fallback linker can also be used on other platforms which are not `zero`.
>> 
>> To initialize the property, VMProps directly reads `jdk.internal.foreig.CABI::current()`. Since this class is in an internal package, `--add-exports` flags are added as javac flags and VM flags for the extra prop definitions class.
>
> Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 44 commits:
> 
>  - Merge branch 'master' into VMProps
>  - use only jdk.CABI property
>  - use extra props to check for linker
>  - Add fallbackLinker vmprop
>  - Merge pull request #3 from JornVernee/IsForeignLinkerSupported
>    
>    rename has_port
>  - rename has_port
>  - Merge pull request #2 from JornVernee/WSL_BB
>    
>    account for missing functional in WSL in TestByteBuffer
>  - account for missing mincore on WSL in TestByteBuffer
>  - Merge branch 'master' into PR_21_V2
>  - 8305369: Issues in zero-length memory segment javadoc section
>  - ... and 34 more: https://git.openjdk.org/jdk/compare/b827ce83...8a6df30e

Thanks for the reveiw. I've added a comment that explains the property.

During testing after the merge I noticed that the `@requires` tags were checking against `"UNKNOWN"` while they should have been checking against `"UNSUPPORTED"`.

I've fixed this and re-tested on the following configurations:

- Windows/x64, tests full port
- Windows/x86, tests UNSUPPORTED (I also needed to fix an unrelated issues in one of the native test libraries for this to work. That is not included in this patch)
- Linux/x64 with CABI set to FALLBACK
- Linux/x64/zero (also FALLBACK)

For the latter two to pass, I had to fix an issue in `TestLinker` as well, where some test cases brought in by the merge with master were failing on the fallback linker, since it doesn't support by-value unions. The fix conditionally adds those test cases only when we are not running on the fallback linker.

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

PR Comment: https://git.openjdk.org/jdk/pull/13429#issuecomment-1529932049