Patch boot/common/relocate.S to start kernel at 0x000c

Dale Farnsworth dale at
Wed Mar 5 10:08:49 EST 2003

On Tue, Mar 04, 2003 at 08:21:03PM +0000, Dan Malek wrote:
> Well, one option that may be the easiest is to just change all
> of the linux head.S files to have the three nops again.  When we
> split these file apart a while back, we just removed everything that
> wasn't necessary.  Just put a note in those files why they are
> present.  They don't cost anything since these are exception vector
> locations or temporary storage locations for special purposes.

What about this approach?

The problem is that on some systems, the cpu 1 runs at
__secondary_hold before cpu 0 runs at _start and __secondary_hold
overwrites the nop at 0x4.

If we branch around the the the word at 0x4, the kernel can start
at 0 and we don't need to modify the other head.S files.

The following patch works on my SMP system.


===== head.S 1.80 vs edited =====
--- 1.80/arch/ppc/kernel/head.S	Thu Feb 27 12:40:15 2003
+++ edited/head.S	Tue Mar  4 15:52:24 2003
@@ -88,8 +88,13 @@
 	 * but we're always started by some kind of bootloader now.
 	 *  -- Cort
-	nop	/* used by __secondary_hold on prep (mtx) and chrp smp */
-	nop	/* used by __secondary_hold on prep (mtx) and chrp smp */
+	/*
+	 * The first two words are used by __secondary_hold on SMP systems.
+	 * The second word may be overwritten before the first cpu runs
+	 * here, so we branch around it.
+	 */
+	b	__start
+	nop

 /* PMAC

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