linux-kernel - Re: [PATCH 08/17] binfmt_flat: consolidate two version of flat_v2_reloc

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Message-ID: <CAMuHMdXkMh+pOqPNavmYAhKXTVT12nC5gKc10CJj_CXME+uhWQ@mail.gmail.com>
Date:   Wed, 26 Jun 2019 10:18:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg Ungerer <gerg@...ux-m68k.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
        Michal Simek <monstr@...str.eu>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-c6x-dev@...ux-c6x.org,
        "moderated list:H8/300 ARCHITECTURE" 
        <uclinux-h8-devel@...ts.sourceforge.jp>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linux-riscv@...ts.infradead.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        linux-xtensa@...ux-xtensa.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/17] binfmt_flat: consolidate two version of flat_v2_reloc_t

Hi Greg,

On Wed, Jun 26, 2019 at 9:23 AM Greg Ungerer <gerg@...ux-m68k.org> 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@....de>
> >> ---
> >>   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?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds