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List: linux-sh
Subject: Re: [PATCH 08/17] binfmt_flat: consolidate two version of flat_v2_reloc_t
From: Greg Ungerer <gregungerer00 () gmail ! com>
Date: 2019-06-26 12:14:06
Message-ID: a2567a04-ac83-408f-51a2-53d23fcc0c36 () linux-m68k ! org
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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@linux-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@lst.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
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