powerpc: Fix bad inline asm constraint in create_zero_mask()

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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.

Cc: stable@vger.kernel.org
Fixes: d0cebfa650 ("powerpc: word-at-a-time optimization for 64-bit Little Endian")
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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This commit is contained in:

Anton Blanchard 2016-04-30 08:29:27 +10:00 • committed by Michael Ellerman

parent d701cca674

commit b4c112114a

1 changed files with 1 additions and 1 deletions

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arch/powerpc/include/asm/word-at-a-time.h

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