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

[Greg Ungerer <gerg@linux-m68k.org>]

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@thingy.jp>

Seems to make sense from what we have in memcpy.c.

Acked-by: Greg Ungerer <gerg@linux-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;