Re: [PATCH] Fix eisa_mmap evaluation, add memory existence check

[Robert Millan]

On Tue, Oct 23, 2007 at 09:06:16PM +0200, Christian Franke wrote:
> +/* Check memory address */
> +static int
> +addr_is_valid (grub_addr_t addr)
> +{
> +  volatile unsigned char * p = (volatile unsigned char *)addr;
> +  unsigned char x, y;
> +  x = *p;
> +  *p = x ^ 0xcf;
> +  y = *p;
> +  *p = x;
> +  return y == (x ^ 0xcf);
> +}

0xff would be better IMO.

> +  if (!(addr + size > addr && addr_is_valid (addr) && addr_is_valid 
> (addr+size-1)))
> +    grub_fatal ("invalid memory region %p - %p", (char*)addr, 
> (char*)addr+size-1);

Should `addr + size > addr' be optimized out as `size > 0' ?  (or if we need it
this way to check for overflows, should we prevent gcc from optimizing it?)

-- 
Robert Millan

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