Re: [PATCH] hw/display/tcx: use memmove instead of memcpy for overlapping blit memory regions

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Sep 15, 2026 at 07:20:46PM +0300, Николай Зорин wrote:
> SWSA#34e3af79-c6c2-4ad2-986f-313c1ce28e5a

  ^^^^^^^^^  what is this ?

I'm guessing it is a tag you're using for tracking issues, but
if so, it should be removed before sending commits upstream.

> 
> In `tcx_blit_writel()`, memory copying occurs within the same video RAM
> buffers (`vram` and `vram24`) using source and destination offsets that
> can potentially overlap during blit operations.
> 
> Using `memcpy()` on overlapping memory regions triggers undefined behavior
> according to the C standard. Depending on compiler optimizations, this
> can lead to graphical artifacts, memory corruption, or unexpected
> behavior in the guest system.
> 
> Fix this by replacing `memcpy()` with `memmove()`, which explicitly
> guarantees safe and correct behavior when memory regions overlap.
> 
> Signed-off-by: Nikolay N Zorin <zorin@swemel.ru>
> ---
>  hw/display/tcx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/display/tcx.c b/hw/display/tcx.c
> index 2cfc1e8f..fb48a199 100644
> --- a/hw/display/tcx.c
> +++ b/hw/display/tcx.c
> @@ -587,9 +587,9 @@ static void tcx_blit_writel(void *opaque, hwaddr addr,
>                  }
>              }
>          } else {
> -            memcpy(&s->vram[addr], &s->vram[adsr], len);
> +            memmove(&s->vram[addr], &s->vram[adsr], len);
>              if (s->depth == 24) {
> -                memcpy(&s->vram24[addr], &s->vram24[adsr], len * 4);
> +                memmove(&s->vram24[addr], &s->vram24[adsr], len * 4);
>              }
>          }
>          tcx_set_dirty(s, addr, len);
> -- 
> 2.43.0
> 
> 

With regards,
Daniel
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