Re: [PATCH 08/17] binfmt_flat: consolidate two version of flat_v2_reloc_t

[Greg Ungerer]

Hi Geert,

On 26/6/19 6:18 pm, Geert Uytterhoeven wrote:
> Hi Greg,
>
> On Wed, Jun 26, 2019 at 9:23 AM Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
> > On 26/6/19 8:29 am, Al Viro wrote:
> > > On Thu, Jun 13, 2019 at 09:08:54AM +0200, Christoph Hellwig wrote:
> > > > Two branches of the ifdef maze actually have the same content, so merge
> > > > them.
> > > >
> > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > > > ---
> > > >    include/linux/flat.h | 6 ++----
> > > >    1 file changed, 2 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/include/linux/flat.h b/include/linux/flat.h
> > > > index 2b7cda6e9c1b..19c586b74b99 100644
> > > > --- a/include/linux/flat.h
> > > > +++ b/include/linux/flat.h
> > > > @@ -69,15 +69,13 @@ struct flat_hdr {
> > > >    typedef union {
> > > >       unsigned long   value;
> > > >       struct {
> > > > -# if defined(mc68000) && !defined(CONFIG_COLDFIRE)
> > > > +#if defined(__LITTLE_ENDIAN_BITFIELD) || \
> > > > +    (defined(mc68000) && !defined(CONFIG_COLDFIRE))
> > > >               signed long offset : 30;
> > > >               unsigned long type : 2;
> > > >    # elif defined(__BIG_ENDIAN_BITFIELD)
> > > >               unsigned long type : 2;
> > > >               signed long offset : 30;
> > > > -# elif defined(__LITTLE_ENDIAN_BITFIELD)
> > > > -            signed long offset : 30;
> > > > -            unsigned long type : 2;
> > > >    # else
> > > >    #          error "Unknown bitfield order for flat files."
> > > >    # endif
> > > > --
> > > > 2.20.1
> > >
> > > FWIW, I wonder if keeping that type is worth bothering.
> > > Something like
> > > old_reloc(__be32 reloc)
> > > {
> > >        u32 v = be32_to_cpu(reloc);
> > >        int offset, type;
> > >
> > > #if (defined(mc68000) && !defined(CONFIG_COLDFIRE))
> > >        /* old m68k uses unusual format - type is in lower bits of octet 3 */
> > >        type = v % 4;
> > >        offset = (int)v / 4;
> > > #else
> > >        /* everything else (including coldfire) has it in upper bits of octet 0 */
> > >        type = v >> 30;
> > >        offset = (int)(v << 2) >> 2; /* or (v & 0x1fffffff) - (v & 0x20000000) * 4 */
> > > #endif
> > >        ...
> > >
> > > and to hell with bitfields, aliasing unions, etc.  Unless I'm misreading
> > > the whole thing, that is...  Greg?
> >
> > I think you are right. This is much better.
> > The old mc6800 is the odd one out, the rest have it in network order,
> > and this makes that much clearer.
>
> Is that correct for Microblaze, which can be big or little endian?

It is true for all architectures that use flat. All fields inside a
flat format binary are store in network order.

The final processing of the relocation entries in the elf2flt
converter tool:

   for (i=0; i<reloc_len; i++) reloc[i] = htonl(reloc[i]);

Regards
Greg