[PATCH] ARM: bitops: Fix low-level code to be Thumb-2 compatible

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Wed, Feb 02, 2011 at 02:33:55PM -0500, Nicolas Pitre wrote:
> On Wed, 2 Feb 2011, Dave Martin wrote:
> 
> > The new bitops code cunningly str <Rt>, [r1, -r1] to trigger
> > a fault by attempting to store to address zero.
> > 
> > This code doesn't assemble in Thumb-2, since Thumb-2 doesn't
> > allow negative register offsets at all for loads and stores.
> > 
> > The patch loads 0 into r2 and uses that as a base register
> > instead for the Thumb-2 case: r2 seems non-live at every
> > instance of this problem.
> > 
> > The ARM case is unaffected.
> > 
> > Signed-off-by: Dave Martin <dave.martin@linaro.org>
> 
> Russell proposed a better solution already:
> 
> http://mid.gmane.org/alpine.LFD.2.00.1101181312360.8580 at xanadu.home
> 
> No idea why this wasn't folded in his series yet though.

Now added, and original tested-by's dropped.  It now needs re-testing.

8<----
Subject: [PATCH] ARM: bitops: ensure set/clear/change bitops take a word-aligned pointer

Add additional instructions to our assembly bitops functions to ensure
that they only operate on word-aligned pointers.  This will be necessary
when we switch these operations to use the word-based exclusive
operations.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 arch/arm/lib/bitops.h |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/lib/bitops.h b/arch/arm/lib/bitops.h
index d422529..bd00551 100644
--- a/arch/arm/lib/bitops.h
+++ b/arch/arm/lib/bitops.h
@@ -1,6 +1,8 @@
 
 #if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_CPU_32v6K)
 	.macro	bitop, instr
+	ands	ip, r1, #3
+	strneb	r1, [ip]		@ assert word-aligned
 	mov	r2, #1
 	and	r3, r0, #7		@ Get bit offset
 	add	r1, r1, r0, lsr #3	@ Get byte offset
@@ -14,6 +16,8 @@
 	.endm
 
 	.macro	testop, instr, store
+	ands	ip, r1, #3
+	strneb	r1, [ip]		@ assert word-aligned
 	and	r3, r0, #7		@ Get bit offset
 	mov	r2, #1
 	add	r1, r1, r0, lsr #3	@ Get byte offset
@@ -32,6 +36,8 @@
 	.endm
 #else
 	.macro	bitop, instr
+	ands	ip, r1, #3
+	strneb	r1, [ip]		@ assert word-aligned
 	and	r2, r0, #7
 	mov	r3, #1
 	mov	r3, r3, lsl r2
@@ -52,6 +58,8 @@
  * to avoid dirtying the data cache.
  */
 	.macro	testop, instr, store
+	ands	ip, r1, #3
+	strneb	r1, [ip]		@ assert word-aligned
 	add	r1, r1, r0, lsr #3
 	and	r3, r0, #7
 	mov	r0, #1
-- 
1.6.2.5