Messages in this thread | | | Date | Wed, 9 Apr 2014 17:13:26 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option |
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Hello Russell,
On Wed, Apr 09, 2014 at 04:06:40PM +0100, Russell King - ARM Linux wrote: > On Wed, Apr 09, 2014 at 04:54:16PM +0200, Jonas Jensen wrote: > > On 13 December 2013 12:39, Russell King - ARM Linux > > <linux@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? The added b . was a test to check if the machine then hangs instead of crashing. (And yes, that was the case, so it was tried to return to a non-aligned address.)
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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