提交 b4c11211 编写于 作者: A Anton Blanchard 提交者: Michael Ellerman

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.

Cc: stable@vger.kernel.org
Fixes: d0cebfa6 ("powerpc: word-at-a-time optimization for 64-bit Little Endian")
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
上级 d701cca6
......@@ -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;
}
......
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