powerpc: create_zero_mask() has bad inline assembly constraint

[Michael Ellerman]

On Fri, 2016-29-04 at 22:29:27 UTC, Unknown sender due to SPF wrote:
> 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.
> 
> Signed-off-by: Anton Blanchard <anton at samba.org>
> Cc: <stable at vger.kernel.org>
> Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian")

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/b4c112114aab9aff5ed4568ca5

cheers