Re: Natural alignment used on NetBSD/m68k

[John Paul Adrian Glaubitz <glaubitz%physik.fu-berlin.de@localhost>]

Hello,

On Sat, 2025-02-08 at 11:37 +0000, John Klos wrote:
> > can anyone tell me whether NetBSD/m68k uses a natural alignment of two 
> > or four bytes? I'm asking since Linux/m68k defaults to two bytes 
> > alignment which has started to become a burden as more and more programs 
> > require at least four bytes alignment these days. Software that is 
> > affected includes CPython, LLVM, Mold, gccgo and many more.
> 
> NetBSD uses four bytes.

OK, thanks for the confirmation.

Do you happen to know what other m68k Unices use such as SunOS?

> > As Debian's m68k maintainer, I have been trying to convince the 
> > community to switch to four bytes alignment, but so far an agreement has 
> > not been made. On the other hand, the original SysV Unix ABI released by 
> > Motorola [1] defaults to four bytes alignment.
> 
> I've read some of the discussions about that. Your efforts are valiant and 
> appreciated. While I understand the resistance to change, what I don't 
> understand is how some people can think it can or should just simply never 
> change.

Yeah, it's such a frustrating discussion. But the fact that NetBSD uses four
bytes alignment is a huge argument in favor of that change.

Do you happen to know whether NetBSD has always used four bytes or did that
change in the past?

> Of course it'd be great to switch, and I've wondered if there could be 
> some simple way to identify old versus new binaries so you wouldn't need a 
> compatibility flag day.
> 
> > And maybe someone could compile and run the following code on a 
> > NetBSD/m68k instance to confirm the alignment to be four bytes:
> > 
> > #include <stdio.h>
> > 
> > typedef struct { char x; int y; } test_t;
> > 
> > int main(void)
> > {
> >    printf("%d\n", sizeof(test_t) / 2);
> > }
> 
> 4 :)

Thanks a lot for the confirmation!

Adrian

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