On Wed, 17 May 2023 11:15:11 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> The FFM API exposes layout constants for Java primitives. Among those there
>> are constants for `JAVA_LONG` and `JAVA_DOUBLE`. Currently, the alignment of
>> these layouts is set the same as their size (e.g. 8 bytes).
>>
>> This is obviously correct on 64-bit platforms, but on 32-bit platform it is
>> not, as such platforms cannot guarantee that doubles and longs will be
>> always 64-bit aligned. This will also result in problems when trying to use
>> e.g. `JAVA_DOUBLE` to model a C double for the linker API on 32-bit
>> platforms.
>>
>> For these reasons, it would be preferable to define the alignment of
>> `JAVA_LONG` and `JAVA_DOUBLE` constants as `ADDRESS.byteSize()`.
>>
>> This patch rectifies alignment of those layout constants to reflect
>> platform-dependent constraints. It also fixes the maximum alignment
>> constraint supported by heap segments, so that it is 4 for long[] and
>> double[] on 32-bit platforms.
>
> Maurizio Cimadamore has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Fix max alignment constants
Marked as reviewed by psandoz (Reviewer).
src/java.base/share/classes/java/lang/foreign/ValueLayout.java line 488:
> 486: /**
> 487: * A value layout constant whose size is the same as that of a Java
> {@code long},
> 488: * bit alignment set to {@code ADDRESS.bitSize()}, and byte order
> set to {@link ByteOrder#nativeOrder()}.
Suggestion:
* (platform dependent) bit alignment set to {@code ADDRESS.bitSize()}, and
byte order set to {@link ByteOrder#nativeOrder()}.
?
-------------
PR Review: https://git.openjdk.org/jdk/pull/14007#pullrequestreview-1431604601
PR Review Comment: https://git.openjdk.org/jdk/pull/14007#discussion_r1197038551
