Messages in this thread | | | Date | Wed, 9 Apr 2014 17:04:48 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option |
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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 > #else > mov pc, \reg > > > With this applied, and the following two possibilities in next-20140403: > > [1] ARCH_MULTI_V4 only (no CONFIG_ARM_THUMB) > CONFIG_CPU_32v4=y > > [2] ARCH_MULTI_V4 and ARCH_MULTI_V4T > CONFIG_ARM_THUMB=y > CONFIG_CPU_32v4=y > CONFIG_CPU_32v4T=y > > > Booting a kernel with either option [1] or [2] yield the following results: > > [1] works > [2] hangs after "[ 2.730000] Freeing unused kernel memory: 104K > (c02f5000 - c030f000)" > > > Any help why the moveq doesn't work would be much appreciated. doing s/moveq/mov/ does the trick on the machine in question, but this is obviously not an option for mainline. But it means that even on this non-Thumb capable machine \reg contains an address that is not aligned.
Where does \reg come from? Is it provided by userspace? If so, is it a userspace bug?
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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