[PATCH] opcodes/aarch64: convert print_sme_za_list()'s zan[] / zan_v[]

[Richard Earnshaw (lists)]

On 28/07/2025 17:00, Jan Beulich wrote:
> Merge them into a single array of struct type. There's further no reason
> to have the compiler materialize such objects on the stack. And there's
> also no reason to allow the array(s) to be modifiable. Finally, given
> how short the strings are, there's little point using more space to
> store pointers to them (on 64-bit hosts; the situation is a little
> better on 32-bit ones).
> 
> While there also correct indentation in adjacent code, and avoid open-
> coding ARRAY_SIZE().

OK.

> ---
> The use of snprintf() there also looks questionable: It still assumes
> large enough a buffer is passed in. In which case one could as well use
> sprintf().

Yes it looks like the author mis-read the manual page.

A better fix would be to insert

  if (k >= size) return;

after each call, since a single call to snprintf will never overrun the (remaining) buffer and we just need to ensure that size - k never wraps as an unsigned value.

That still doesn't address the case of snprintf returning a negative value, but with c99 or later, that should only happen for
invalid operands and I don't think they can occur here.

R.

> 
> --- a/opcodes/aarch64-opc.c
> +++ b/opcodes/aarch64-opc.c
> @@ -4016,28 +4016,41 @@ static void
>  print_sme_za_list (char *buf, size_t size, int mask,
>  		   struct aarch64_styler *styler)
>  {
> -  const char* zan[] = { "za",    "za0.h", "za1.h", "za0.s",
> -                        "za1.s", "za2.s", "za3.s", "za0.d",
> -                        "za1.d", "za2.d", "za3.d", "za4.d",
> -                        "za5.d", "za6.d", "za7.d", " " };
> -  const int zan_v[] = { 0xff, 0x55, 0xaa, 0x11,
> -                        0x22, 0x44, 0x88, 0x01,
> -                        0x02, 0x04, 0x08, 0x10,
> -                        0x20, 0x40, 0x80, 0x00 };
> -  int i, k;
> -  const int ZAN_SIZE = sizeof(zan) / sizeof(zan[0]);
> +  static const struct {
> +    unsigned char mask;
> +    char name[7];
> +  } zan[] = {
> +    { 0xff, "za" },
> +    { 0x55, "za0.h" },
> +    { 0xaa, "za1.h" },
> +    { 0x11, "za0.s" },
> +    { 0x22, "za1.s" },
> +    { 0x44, "za2.s" },
> +    { 0x88, "za3.s" },
> +    { 0x01, "za0.d" },
> +    { 0x02, "za1.d" },
> +    { 0x04, "za2.d" },
> +    { 0x08, "za3.d" },
> +    { 0x10, "za4.d" },
> +    { 0x20, "za5.d" },
> +    { 0x40, "za6.d" },
> +    { 0x80, "za7.d" },
> +    { 0x00, " " },
> +  };
> +  int k;
>  
>    k = snprintf (buf, size, "{");
> -  for (i = 0; i < ZAN_SIZE; i++)
> +  for (unsigned int i = 0; i < ARRAY_SIZE (zan); i++)
>      {
> -      if ((mask & zan_v[i]) == zan_v[i])
> -        {
> -          mask &= ~zan_v[i];
> -          if (k > 1)
> +      if ((mask & zan[i].mask) == zan[i].mask)
> +	{
> +	  mask &= ~zan[i].mask;
> +	  if (k > 1)
>  	    k += snprintf (buf + k, size - k, ", ");
>  
> -	  k += snprintf (buf + k, size - k, "%s", style_reg (styler, zan[i]));
> -        }
> +	  k += snprintf (buf + k, size - k, "%s",
> +			 style_reg (styler, zan[i].name));
> +	}
>        if (mask == 0)
>          break;
>      }