From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: barebox@lists.infradead.org, Alexander Kurz <akurz@blala.de>
Subject: Re: [PATCH] arm/cpu/lowlevel: fix: possible processor mode change
Date: Fri, 4 Mar 2016 08:15:18 +0100 [thread overview]
Message-ID: <20160304071518.GR20323@pengutronix.de> (raw)
In-Reply-To: <20160304070448.GB21869@pengutronix.de>
Hello Sascha,
On Fri, Mar 04, 2016 at 08:04:48AM +0100, Sascha Hauer wrote:
> Hi Alexander,
>
> On Wed, Mar 02, 2016 at 11:51:28PM +0100, Alexander Kurz wrote:
> > This is a re-application of fix 17644b55.
> > arm_cpu_lowlevel_init() will set the processor mode to 0x13 (supervisor).
> > When this function is entered via a different processor mode, register
> > banking will happen to lr (r14), resulting in an invalid return address.
> > This fix will preserve the return address manually.
> >
> > Signed-off-by: Alexander Kurz <akurz@blala.de>
> > ---
> > arch/arm/cpu/lowlevel.S | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/cpu/lowlevel.S b/arch/arm/cpu/lowlevel.S
> > index b76222d..e5baa12 100644
> > --- a/arch/arm/cpu/lowlevel.S
> > +++ b/arch/arm/cpu/lowlevel.S
> > @@ -4,6 +4,8 @@
> >
> > .section ".text_bare_init_","ax"
> > ENTRY(arm_cpu_lowlevel_init)
> > + /* save lr, since it may be banked away with a processor mode change */
> > + mov r2, lr
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> Thanks for fixing this and for adding a comment why this is done. This
> hopefully prevents us from breaking it again.
>
> Out of interest, what system are you using where this fix is necesssary?
>
> Uwe, now we know why that was done and why e190bcf (arm/cpu/lowlevel:
> Don't save the return address in another register) was a bad idea.
Right. :-) But even if I had seen
17644b55cae9c234b26213d644e9fd939b0ec815 back then I would have wondered
because the commit log isn't that verbose :-(
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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next prev parent reply other threads:[~2016-03-04 7:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 22:51 Alexander Kurz
2016-03-04 7:04 ` Sascha Hauer
2016-03-04 7:15 ` Uwe Kleine-König [this message]
2016-03-04 8:43 ` Alexander Kurz
2016-03-04 9:18 ` Uwe Kleine-König
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