[PATCH] Fix stack memory protection on targets where the stack grows upward

[Florian Weimer]

* John David Anglin:

>  #elif _STACK_GROWS_UP
> -	  if (mprotect ((char *) pd - pd->guardsize,
> -			pd->guardsize - guardsize, prot) != 0)
> +	  char *new_guard = (char *)(((uintptr_t) pd - guardsize) & ~pagesize_m1);
> +	  char *old_guard = (char *)(((uintptr_t) pd - pd->guardsize) & ~pagesize_m1);
> +	  /* The guard size difference might be > 0, but once rounded
> +	     to the nearest page the size difference might be zero.  */
> +	  if (new_guard > old_guard
> +	      && mprotect (old_guard, new_guard - old_guard, prot) != 0)
>  	    goto mprot_error;
>  #endif
>  

This is essentially HPPA-specific code, right?  So I guess we can do
whatever it takes there.