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

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Message-ID: <a2567a04-ac83-408f-51a2-53d23fcc0c36@linux-m68k.org>
Date:   Wed, 26 Jun 2019 22:14:06 +1000
From:   Greg Ungerer <gregungerer00@...il.com>
To:     Geert Uytterhoeven <geert@...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 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@...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?

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