On Wed, Apr 09, 2014 at 04:54:16PM +0200, Jonas Jensen wrote:
> On 13 December 2013 12:39, Russell King - ARM Linux
> <li...@arm.linux.org.uk> wrote:
> > I see what's causing this: the kuser helpers are using "bx lr" to return
> > which will be undefined on non-Thumb CPUs. We generally cope fine with
> > non-Thumb CPUs, conditionalising where necessary on HWCAP_THUMB or the
> > T bit in the PSR being set.
> >
> > However, it looks like the kuser helpers got missed. As a check, please
> > look at arch/arm/kernel/entry-armv.S, find the line with:
> >
> > .macro usr_ret, reg
> >
> > and ensure that the mov pc, \reg case always gets used. Please report
> > back.
>
> Uwe and Arnd came up with a solution except it doesn't work when I test it.
>
> The suggested patch is:
>
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index 1879e8d..de15bfd 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -739,6 +739,18 @@ ENDPROC(__switch_to)
>
> .macro usr_ret, reg
> #ifdef CONFIG_ARM_THUMB
> + /*
> + * Having CONFIG_ARM_THUMB isn't a guarantee that the cpu has support
> + * for Thumb and so the bx instruction. Use a mov if the address to
> + * jump to is 32 bit aligned. (Note that this code is compiled in ARM
> + * mode, so this is the right test.)
> + */
> +#if defined(CONFIG_CPU_32v4)
> + tst \reg, #3
> + moveq pc, \reg
> + b .
> +#endif
> +
> bx \reg
What's wrong with:
tst \reg, #3
moveq pc, \reg
bx \reg
rather than ending in an infinite loop?
--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
