Rusty Russell wrote:
> I don't think so. There's *never* address subtraction, there's
> sometimes 32 bit wrap (glibc uses this to effect subtraction, sure).
> But there's no wrap here.
>
Hm, I guess, so long as you assume the kernel data segment is always
below the kernel heap.
> To test, I changed the following:
>
> --- smpboot.c.~8~ 2006-09-25 15:51:50.000000000 +1000
> +++ smpboot.c 2006-09-25 16:00:36.000000000 +1000
> @@ -926,8 +926,9 @@
> unsigned long per_cpu_off)
> {
> unsigned limit, flags;
> + extern char __per_cpu_end[];
>
> - limit = (1 << 20);
> + limit = PAGE_ALIGN((long)__per_cpu_end) >> PAGE_SHIFT;
>
limit is a size, rather than the end address, so this isn't quite right.
J
