Re: Question on BIGGEST_ALIGNMENT in GCC on NetBSD/m68k

[Laurent Vivier <laurent@vivier.eu>]

Le 16/06/2025 à 12:07, Geert Uytterhoeven a écrit :
> Hi Laurent,
>
> On Mon, 16 Jun 2025 at 11:16, Laurent Vivier <laurent@vivier.eu> wrote:
> > Le 16/06/2025 à 11:00, John Paul Adrian Glaubitz a écrit :
> > > > And there will be a problem with binfmt_misc because we can't rely on
> > > > the ELF signature to know which qemu-user to run, the one with 2byte
> > > > alignment or the one with 4byte alignment?
> > > What about the ELF note [1] that David Brownlee suggested? Can these be used?
> > >
> > > Adrian
> > >
> > > > [1]https://www.netbsd.org/docs/kernel/elf-notes.html
> >
> > binfmt_misc doesn't use the sections to select the interpreter, but the
> > 128 first bytes of the file.
> >
> > I think you need to change the ABI type in the ELF header:
> > https://fr.wikipedia.org/wiki/Executable_and_Linkable_Format
>
> Interesting....
>
> Does any system actually use ABI (byte 7) = 3 (Linux)?
> All of amd64/arm/arm64/ia64/i386/m68k/microblaze/mips(el)/powerpc/risvc/s390/sh/sparc
> seem to use 0 (SYSV).
>
> #define ELFOSABI_NONE   0
> #define ELFOSABI_LINUX  3
>
> Ah, parisc does. And C6x uses 0x40.

You're right. But to update the ELF header with the information we are 
using 4 bytes alignment perhaps we should use instead the e_flags entry?

It's architecture dependent and it seems used by MIPS (EF_MIPS_ABI2 
?)... so MIPS is OK, I think the problem is I don't use the correct 
binfmt_misc mask...

Thanks,
Laurent