From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hr2.samba.org (hr2.samba.org [144.76.82.148]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qxT0821BRzDq5f for ; Sat, 30 Apr 2016 08:29:43 +1000 (AEST) Date: Sat, 30 Apr 2016 08:29:27 +1000 From: Anton Blanchard To: Segher Boessenkool , Michael Ellerman , Paul Mackerras , Benjamin Herrenschmidt , felix@linux.vnet.ibm.com, Bill Schmidt Cc: linuxppc-dev@lists.ozlabs.org Subject: [PATCH] powerpc: create_zero_mask() has bad inline assembly constraint Message-ID: <20160430082927.2111f5ae@kryten> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Cc: Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian") --- diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h index e4396a7..4afe66a 100644 --- a/arch/powerpc/include/asm/word-at-a-time.h +++ b/arch/powerpc/include/asm/word-at-a-time.h @@ -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; }