[RFC PATCH 5/5] ARM: entry: Fix Thumb-2 undef handling for multi-CPU kernels

[Arnd Bergmann]

On Wednesday 10 August 2011, Dave Martin wrote:
> When v6 and >=v7 boards are supported in the same kernel, the
> __und_usr code currently makes a build-time assumption that Thumb-2
> instructions occurring in userspace don't need to be supported.
> Strictly speaking this is incorrect.
> 
> This patch fixes the above case by doing a run-time check on the
> CPU architecture in these cases.  This only affects kernels which
> support v6 and >=v7 CPUs together: plain v6 and plain v7 kernels
> are unaffected.

I think this patch broke random configurations (!THUMB2 && v7) for me:

> @@ -439,7 +440,27 @@ __und_usr:
>  #endif
>  	beq	call_fpe
>  	@ Thumb instruction
> -#if __LINUX_ARM_ARCH__ >= 7
> +#if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7
> +/*
> + * Thumb-2 instruction handling.  Note that because pre-v6 and >= v6 platforms
> + * can never be supported in a single kernel, this code is not applicable at
> + * all when __LINUX_ARM_ARCH__ < 6.  This allows simplifying assumptions to be
> + * made about .arch directives.
> + */
> +#if __LINUX_ARM_ARCH__ < 7
> +/* If the target CPU may not be Thumb-2-capable, a run-time check is needed: */
> +#define NEED_CPU_ARCHITECTURE
> +	ldr	r5, .LCcpu_architecture
> +	ldr	r5, [r5]
> +	cmp	r5, #CPU_ARCH_ARMv7
> +	blo	__und_usr_unknown
> +/*
> + * The following code won't get run unless the running CPU really is v7, so
> + * coding round the lack of ldrht on older arches is pointless.  Temporarily
> + * override the assembler target arch with the minimum required instead:
> + */
> +	.arch	armv6t2
> +#endif
>  2:
>   ARM(	ldrht	r5, [r4], #2	)


This fixes it, please fold into the patch or apply on top.

	Arnd

8<---
ARM: entry: refix Fix Thumb-2 undef handling for multi-CPU kernels

In some configurations labels become obsolete, so don't generate fixups for them.

Signed-off-by: Arnd Bergmann <arnd at arndb.de>

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 9ad50c4..b145f16 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -497,7 +497,7 @@ ENDPROC(__und_usr)
 	.popsection
 	.pushsection __ex_table,"a"
 	.long	1b, 4b
-#if __LINUX_ARM_ARCH__ >= 7
+#if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7
 	.long	2b, 4b
 	.long	3b, 4b
 #endif