FAILED: patch "[PATCH] powerpc: Fix bad inline asm constraint in create_zero_mask()" failed to apply to 3.14-stable tree

The patch below does not apply to the 3.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Anton Blanchard <[email protected]>
Date: Sat, 30 Apr 2016 08:29:27 +1000
Subject: [PATCH] powerpc: Fix bad inline asm constraint in create_zero_mask()

In create_zero_mask() we have:

	addi	%1,%2,-1
	andc	%1,%1,%2
	popcntd	%0,%1

using the "r" constraint for %2. r0 is a valid register in the "r" set, but addi X,r0,X turns it into an li:

	li	r7,-1
	andc	r7,r7,r0
	popcntd	r4,r7

Fix this by using the "b" constraint, for which r0 is not a valid register.

This was found with a kernel build using gcc trunk, narrowed down to when -frename-registers was enabled at -O2. It is just luck however that we aren't seeing this on older toolchains.

Thanks to Segher for working with me to find this issue.

index e4396a7d0f7c..4afe66aa1400 100644
@@ -82,7 +82,7 @@ static inline unsigned long create_zero_mask(unsigned long bits)
 	    "andc	%1,%1,%2\n\t"
 	    "popcntd	%0,%1"
 		: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)
-		: "r" (bits));
+		: "b" (bits));
 
 	return leading_zero_bits;
 }