linux-kernel - Re: [PATCH] m68k: nommu: fix memmove() with differently aligned src and dest for 68000

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Message-ID: <5c2730c2-d969-44af-85f9-4d57c0ad387d@linux-m68k.org>
Date: Fri, 16 Jan 2026 21:03:26 +1000
From: Greg Ungerer <gerg@...ux-m68k.org>
To: Daniel Palmer <daniel@...ngy.jp>, geert@...ux-m68k.org
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: nommu: fix memmove() with differently aligned src
 and dest for 68000

Hi Daniel,

I'll add this to the m68knommu git tree, for-next branch.

Thanks
Greg



On 19/12/25 21:58, Greg Ungerer wrote:
> Hi Daniel,
> 
> On 13/12/25 22:04, Daniel Palmer wrote:
>> 68000 has different alignment needs to 68020+.
>> memcpy() checks if the destination is aligned and does a smaller copy
>> to fix the alignment and then critically for 68000 it checks if the
>> source is still unaligned and if it is reverts to smaller copies.
>>
>> memmove() does not currently do the second part and malfunctions if
>> one of the pointers is aligned and the other isn't.
> 
> What is the nature of the failure, is it a trap?
> 
> 
>> This is apparently getting triggered by printk. If I put breakpoints
>> into the new checks added by this commit the first hit looks like this:
>>
>> memmove (n=205, src=0x2f3971 <printk_shared_pbufs+205>, dest=0x2f3980 <printk_shared_pbufs+220>) at arch/m68k/lib/memmove.c:82
>>
>> Signed-off-by: Daniel Palmer <daniel@...ngy.jp>
> 
> Seems to make sense from what we have in memcpy.c.
> 
> Acked-by: Greg Ungerer <gerg@...ux-m68k.org>
> 
> Geert: if you are ok with this I can take it via the m68knommu tree?
> 
> Regards
> Greg
> 
> 
> 
>> ---
>>
>> This is from my "make 68000 work again" backlog.
>>
>> I have had this fix for years and I think the few other people that
>> have various 68000 hobby builds must have something similar.
>>
>> /root # uname -a
>> uClinux buildroot 6.18.0-12420-gdc1a468a2724 #120 Sat Dec 13 20:42:45 JST 2025 m68k GNU/Linux
>> /root # cat /proc/cpuinfo
>> CPU:            68000
>> MMU:            none
>> FPU:            none
>> Clocking:       1179.1MHz
>> BogoMips:       1758.00
>> Calibration:    879001600 loops
>> /root #
>>
>>   arch/m68k/lib/memmove.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/arch/m68k/lib/memmove.c b/arch/m68k/lib/memmove.c
>> index 6519f7f349f6..e33f00b02e4c 100644
>> --- a/arch/m68k/lib/memmove.c
>> +++ b/arch/m68k/lib/memmove.c
>> @@ -24,6 +24,15 @@ void *memmove(void *dest, const void *src, size_t n)
>>               src = csrc;
>>               n--;
>>           }
>> +#if defined(CONFIG_M68000)
>> +        if ((long)src & 1) {
>> +            char *cdest = dest;
>> +            const char *csrc = src;
>> +            for (; n; n--)
>> +                *cdest++ = *csrc++;
>> +            return xdest;
>> +        }
>> +#endif
>>           if (n > 2 && (long)dest & 2) {
>>               short *sdest = dest;
>>               const short *ssrc = src;
>> @@ -66,6 +75,15 @@ void *memmove(void *dest, const void *src, size_t n)
>>               src = csrc;
>>               n--;
>>           }
>> +#if defined(CONFIG_M68000)
>> +        if ((long)src & 1) {
>> +            char *cdest = dest;
>> +            const char *csrc = src;
>> +            for (; n; n--)
>> +                *--cdest = *--csrc;
>> +            return xdest;
>> +        }
>> +#endif
>>           if (n > 2 && (long)dest & 2) {
>>               short *sdest = dest;
>>               const short *ssrc = src;
>