Re: port-amd64/54052: bump STACK_ALIGNBYTES for COMPAT_LINUX

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2019/03/12 5:15, Joerg Sonnenberger wrote:
> On Mon, Mar 11, 2019 at 05:50:00AM +0000, rokuyama.rk%gmail.com@localhost wrote:
> > > Fix:
> > Index: sys/arch/amd64/include/param.h
> > ===================================================================
> > RCS file: /home/netbsd/src/sys/arch/amd64/include/param.h,v
> > retrieving revision 1.29
> > diff -p -u -r1.29 param.h
> > --- sys/arch/amd64/include/param.h	11 Feb 2019 14:59:32 -0000	1.29
> > +++ sys/arch/amd64/include/param.h	10 Mar 2019 13:12:11 -0000
> > @@ -23,6 +23,8 @@
> >   
> >   #define ALIGNED_POINTER(p,t)	1
> >   
> > +#define STACK_ALIGNBYTES	(16 - 1)	/* COMPAT_LINUX */
> > +
> >   #define ALIGNBYTES32		(sizeof(int) - 1)
> >   #define ALIGN32(p)		(((u_long)(p) + ALIGNBYTES32) &~ALIGNBYTES32)
> >   
>
> I'm puzzled by this patch. Stack alignment should already be 16 Bytes on
> AMD64.

Since we don't currently define STACK_ALIGNBYTES for amd64,
it falls back to __ALIGNBYTES = (8 - 1):

src/sys/sys/param.h
https://nxr.netbsd.org/xref/src/sys/sys/param.h#227
...
   227  #ifndef STACK_ALIGNBYTES
   228  #define STACK_ALIGNBYTES        __ALIGNBYTES
   229  #endif
...

src/sys/arch/amd64/include/cdefs.h
https://nxr.netbsd.org/xref/src/sys/arch/amd64/include/cdefs.h#6
...
     6  #define __ALIGNBYTES            (sizeof(long) - 1)
...

Do you mean this violates x86_64 System V ABI?

Thanks,
rin