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Re: [PATCH, rs6000] Fix aggregate alignment ABI issue


On Wed, Jul 9, 2014 at 12:01 PM, Mike Stump <mikestump@comcast.net> wrote:
> On Jul 9, 2014, at 11:29 AM, Eric Christopher <echristo@gmail.com> wrote:
>>>> - The change only affects rare cases: passing a struct by value that is
>>>>   * not a float/vector special case, and
>>>>   * has a size of 1, 2, 4, 8, or 16 bytes, and
>>>>   * has an alignment requirement of 16 bytes or more
>
>>> I copied the Darwin maintainers and active testers so that they are
>>> explicitly aware of the ABI issue. They can decide if they want to fix
>>> the ABI alignment issue on Darwin.
>
>> Thanks David, In general I'd personally prefer to fix the ABI issues,
>> but PPC darwin is beyond EoL by the original company and I don't have
>> any hardware for it myself - in which case I'll leave it up to our
>> more active testers or someone with hardware. (Mike? Have old ppc
>> hardware sitting around?)
>
> Well, I think from a safety perspective I think it is ok, as the system header files and most libraries I would expect not to align to 16 bytes or more.  The problem with this line of thinking, it only takes 1 structure, in one place that is used often (stat, X11) to completely kill things.  Normally I would do a world build with the change in it, and a fink build with it in it, and if no changes occur, the change is reasonably safe.  I donât have the machines/system to do either unfortunately.  I had been testing ppc with emulation, so I canât do much of that anymore either.
>
> So, I think I will punt to the users that still have G5 darwin, they know who they areâ  Iâd say, lets leave it as is, and if they think it is a good idea as well (that would make it 3 of 3) and can do a test suite run at least with the change, then Iâd approve it.

Completely agreed.

-eric


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