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

[Geert Uytterhoeven]

Hi Daniel,

On Sat, 13 Dec 2025 at 13:04, Daniel Palmer <daniel@xxxxxxxxx> 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.
>
> 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@xxxxxxxxx>

Thanks for your patch, which is now commit 590fe2f46c8698bb ("m68k:
nommu: fix memmove() with differently aligned src and dest for
68000") in v7.0-rc1.

> --- 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)

Ideally, these (and the few existing other checks) should check for
CONFIG_CPU_HAS_NO_UNALIGNED instead.

> +               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;

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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