Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel

From: Jeremy Fitzhardinge
Date: Mon Sep 25 2006 - 02:25:52 EST

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.

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