lkml.org 
[lkml]   [2006]   [Sep]   [25]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH 5/7] Use %gs for per-cpu sections in kernel
FromRusty Russell <>
DateMon, 25 Sep 2006 16:03:52 +1000
On Sun, 2006-09-24 at 22:25 -0700, Jeremy Fitzhardinge wrote:
> The %gs:per_cpu__foo addressing mode still calculates 
> 0xbcef00+0xc0433800, which is still a subtraction.  My essential point 
> is that *all* kernel addresses (=kernel symbols) are negative, so using 
> them as an offset from a segment base (any segment base) is a 
> subtraction, which requires a 4G limit.

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.

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;
 	flags = 0x8;		/* 4k granularity */
 
 	/* present read-write data segment */

Works fine...

Hope that clarifies!
Rusty.
-- 
Help! Save Australia from the worst of the DMCA: http://linux.org.au/law

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-09-25 08:07    [from the cache]
©2003-2008