On Mon, 7 Oct 2024 11:27:33 GMT, Vladimir Kozelkov <d...@openjdk.org> wrote:
> Another test example. I can create a structure ending with PaddingLayout
>
> ```
> {
> Linker linker = Linker.nativeLinker();
> var sequence0a8 = MemoryLayout.sequenceLayout(0, JAVA_LONG);
> var sequence3a1 = MemoryLayout.sequenceLayout(3, JAVA_BYTE);
> var padding5a1 = MemoryLayout.paddingLayout(5);
> var struct8a8 = MemoryLayout.structLayout(sequence0a8, sequence3a1,
> padding5a1);
> var fd = FunctionDescriptor.of(struct8a8, struct8a8, struct8a8);
> linker.downcallHandle(fd);
> }
> ```
>
> Is it just me or is this a legal way to create an over-aligned layout?
>
> ```
> {
> Linker linker = Linker.nativeLinker();
> var sequence0a8 = MemoryLayout.sequenceLayout(0, JAVA_LONG);
> var sequence8a1 = MemoryLayout.sequenceLayout(8, JAVA_BYTE);
> var struct8a8 = MemoryLayout.structLayout(sequence0a8, sequence8a1);
> var fd = FunctionDescriptor.of(struct8a8, struct8a8, struct8a8);
> linker.downcallHandle(fd);
> }
> ```
>
> If I remove the PaddingLayout, the structure appears to be completely normal,
> except that it doesn't contain a single real element that needs alignment 8
I think the new rules should explicitly ban zero-element sequence layouts.
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PR Comment: https://git.openjdk.org/jdk/pull/21041#issuecomment-2396840477
