Re: [PATCH V5 2/3] Add AVX512 register support to gdbserver.

[Andreas Arnez <arnez@linux.vnet.ibm.com>]

Hi,

While building GDB I encountered a gcc warning (array subscript above
array bounds) and tracked it down to the patch below.

On Wed, Apr 23 2014, Michael Sturm wrote:

>  # Linux object files.  This is so we don't have to repeat
> diff --git a/gdb/gdbserver/i387-fp.c b/gdb/gdbserver/i387-fp.c
> index e655f74..c2d0bdf 100644
> --- a/gdb/gdbserver/i387-fp.c
> +++ b/gdb/gdbserver/i387-fp.c
> @@ -22,6 +22,11 @@
>  
>  static const int num_mpx_bnd_registers = 4;
>  static const int num_mpx_cfg_registers = 2;
> +static const int num_avx512_k_registers = 8;
> +static const int num_avx512_zmmh_low_registers = 16;
> +static const int num_avx512_zmmh_high_registers = 16;
> +static const int num_avx512_ymmh_registers = 16;
> +static const int num_avx512_xmm_registers = 16;
>  
>  /* Note: These functions preserve the reserved bits in control registers.
>     However, gdbserver promptly throws away that information.  */
> @@ -120,6 +125,17 @@ struct i387_xsave {
>    /* Space for 2 MPX configuration registers of 64 bits
>       plus reserved space.  */
>    unsigned char mpx_cfg_space[16];
> +
> +  unsigned char reserved5[48];
> +
> +  /* Space for 8 OpMask register values of 64 bits.  */
> +  unsigned char k_space[64];
> +
> +  /* Space for 16 256-bit zmm0-15.  */
> +  unsigned char zmmh_low_space[512];
> +
> +  /* Space for 16 512-bit zmm16-31 values.  */
> +  unsigned char zmmh_high_space[1024];
>  };
>
> [...]
> +
> +  /* Check if any of ZMM16H-ZMM31H registers are changed.  */
> +  if ((x86_xcr0 & I386_XSTATE_ZMM))
> +    {
> +      int zmm16h_regnum = find_regno (regcache->tdesc, "zmm16h");
> +
> +      for (i = 0; i < num_avx512_zmmh_high_registers; i++)
> +	{
> +	  collect_register (regcache, i + zmm16h_regnum, raw);
> +	  p = ((char *) &fp->zmmh_low_space[0]) + 32 + i * 64;
                             ^^^^^^^^^^^^^^
Should this really mean 'zmm_high_space'?

> +	  if (memcmp (raw, p, 32) != 0)

The warning occurs for this memcmp().

> +	    {
> +	      xstate_bv |= I386_XSTATE_ZMM;
> +	      memcpy (p, raw, 32);
> +	    }
> +	}
> +    }