RFR: 8306901: Macro offset_of confuses Eclipse CDT

[Thomas Stuefe]

On Thu, 27 Apr 2023 08:41:35 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> > > > Also I wonder whether the ATTRIBUTE_ALIGNED(16) would be more correctly `alignas(klass)` but that is pre-existing.
> > > 
> > > 
> > > Probably :) At least it would be cleaner in my eyes than the hard coded 16. With this pr I'd like to address just the CDT issue though.
> > 
> > 
> > I believe the trick may not work if the type were artificially aligned to something larger than16, e.g. struct XX alignas(64). I guess that depends on what the compiler does when casting a pointer with a smaller alignment to something with a larger alignemnt.
> 
> Maybe. I'm not familiar enough with `alignas` right now. Also I would have to 'meditate' a bit about [the alignas-part in the hotspot-style guide](https://github.com/openjdk/jdk/blob/master/doc/hotspot-style.md#alignas). Right now I wouldn't expect extended alignment of a type to affect member offsets. But that might be naive.

Checked with GCC and clang, it seems to work. But I think its still UB (otherwise we could just omit the ALIGN specifier completely).

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

PR Comment: https://git.openjdk.org/jdk/pull/13668#issuecomment-1525338929