linux-kernel - Re: Dynamic nop selection breaks boot on Geode LX

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Date:	Sun, 3 Oct 2010 07:50:13 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel Drake <dsd@...top.org>
Cc:	jbaron@...hat.com, Andres Salomon <dilinger@...ued.net>,
	Chris Ball <cjb@...top.org>, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org
Subject: Re: Dynamic nop selection breaks boot on Geode LX

From: Daniel Drake <dsd@...top.org>
Date: Sat, Oct 02, 2010 at 08:16:19PM +0100

> Hi,
>
> linux-next fails to boot on OLPC's XO-1 laptop based on Geode LX
> processor.
>
> This is because of
>
> commit f49aa448561fe9215f43405cac6f31eb86317792 Author: Jason Baron
> <jbaron@...hat.com> Date: Fri Sep 17 11:08:51 2010 -0400
>
>     jump label: Make dynamic no-op selection available outside of
> ftrace
>
> http://git.kernel.org/?p=linux/kernel/git/mingo/linux-2.6-x86.git;a=co
> mmitdiff;h=f49aa44
>
> The Geode hangs inside the asm() statement inside
> arch_init_ideal_nop5.
>
> Any thoughts?

maybe because the Geode doesn't have both the
P6_NOP5 and the NOP with 4 0x66 prefixes:
http://kerneltrap.org/mailarchive/linux-kernel/2010/8/27/4612336

and for some reason the trap can't find the fixup address. You say
"hangs" so you don't even get an "invalid opcode" OOPS?

Maybe on a Geode jmp label should use the 2-byte jmp + 3 1-byte nops
unconditionally after adding a synthetic CPUID flag in init_amd_k6(), in
the Geode part.

-- 
Regards/Gruss,
    Boris.
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