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Commit 7c612bfd authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Russell King
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[ARM] 3210/1: add missing memory barrier helper for NPTL support 



Patch from Nicolas Pitre

Strictly speaking, the NPTL kernel helpers are required for pre ARMv6
only.  They are available on ARMv6+ as well for obvious compatibility
reasons.  However there are cases where extra memory barriers are needed
when using an SMP ARMv6 machine but not on pre-ARMv6.

This patch adds a memory barrier kernel helper that glibc can use as
needed for pre-ARMv6 binaries to be forward compatible with an SMP
kernel on ARMv6, as well as the necessary dmb instructions to the
cmpxchg helper.

Signed-off-by: default avatarNicolas Pitre <nico@cam.org>
Acked-by: default avatarDaniel Jacobowitz <dan@codesourcery.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 567bd980

arch/arm/kernel/entry-armv.S

+49 −0
Original line number Diff line number Diff line
@@ -611,6 +611,47 @@ ENTRY(__switch_to) 
	.globl	__kuser_helper_start

__kuser_helper_start:



/*

 * Reference prototype:

 *

 *	void __kernel_memory_barrier(void)

 *

 * Input:

 *

 *	lr = return address

 *

 * Output:

 *

 *	none

 *

 * Clobbered:

 *

 *	the Z flag might be lost

 *

 * Definition and user space usage example:

 *

 *	typedef void (__kernel_dmb_t)(void);

 *	#define __kernel_dmb (*(__kernel_dmb_t *)0xffff0fa0)

 *

 * Apply any needed memory barrier to preserve consistency with data modified

 * manually and __kuser_cmpxchg usage.

 *

 * This could be used as follows:

 *

 * #define __kernel_dmb() \

 *         asm volatile ( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #95" \

 *	        : : : "lr","cc" )

 */



__kuser_memory_barrier:				@ 0xffff0fa0



#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)

	mcr	p15, 0, r0, c7, c10, 5	@ dmb

#endif

	mov	pc, lr



	.align	5



/*

 * Reference prototype:

 *
@@ -642,6 +683,8 @@ __kuser_helper_start: 
 * The C flag is also set if *ptr was changed to allow for assembly

 * optimization in the calling code.

 *

 * Note: this routine already includes memory barriers as needed.

 *

 * For example, a user space atomic_add implementation could look like this:

 *

 * #define atomic_add(ptr, val) \
@@ -698,10 +741,16 @@ __kuser_cmpxchg: @ 0xffff0fc0 


#else



#ifdef CONFIG_SMP

	mcr	p15, 0, r0, c7, c10, 5	@ dmb

#endif

	ldrex	r3, [r2]

	subs	r3, r3, r0

	strexeq	r3, r1, [r2]

	rsbs	r0, r3, #0

#ifdef CONFIG_SMP

	mcr	p15, 0, r0, c7, c10, 5	@ dmb

#endif

	mov	pc, lr



#endif