RFR: 8304006: jlink should create the jimage file in the native endian for the target platform [v8]

[Mandy Chung]

On Mon, 13 Mar 2023 16:22:30 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> Can I please get a review for this change which proposes to fix the issue reported in https://bugs.openjdk.org/browse/JDK-8206890?
>> 
>> The `jlink` command allows a `--endian` option to specify the byte order in the generated image. Before this change, when such a image was being launched, the code would assume the byte order in the image to be the native order of the host where the image is being launched. That would result in failure to launch java, as noted in the linked issue.
>> 
>> The commit in this PR, changes relevant places to not assume native order and instead determine the byte order by reading the magic bytes in the image file's header content.
>> 
>> A new jtreg test has been added which reproduces the issue and verifies the fix.
>
> Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   don't hardcode the .jmod extension while determining java.base module location

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/JlinkTask.java line 834:

> 832:                     // find the target platform's arch and thus its endianness from the java.base
> 833:                     // module's ModuleTarget attribute
> 834:                     Optional<ResolvedModule> javaBase = cf.findModule("java.base");

`ModuleTarget` is read by `DefaultImageReader::storeFiles` as well.   Perhaps it should be refactored so that the target `Platform` can be passed to `DefaultImageBuilder`.

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/JlinkTask.java line 953:

> 951:         // and supported for creating an image through jlink. Else returns null.
> 952:         private static ByteOrder getNativeEndianOfTargetPlatform(String targetPlatform) {
> 953:             int index = targetPlatform.indexOf("-"); // of the form <operating system>-<arch>

`Platform::parsePlatform` is the utility method to parse `ModuleTarget`.   It can be updated to include additional architectures.

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PR: https://git.openjdk.org/jdk/pull/11943