Fix GCC asm constraints in crypto/bn/asm/x86_64-gcc.c

[Florian Weimer]

When x32 support was added to this file, the "&" constraint was dropped, 
allowing GCC to overlap register assignments for inputs and outputs, 
resulting in broken assembler code.

--
Florian Weimer / Red Hat Product Security Team
commit 9dbf28460d10387c819d332b7a5c0397942b75ee
Author: Florian Weimer <fwei...@redhat.com>
Date:   Mon Nov 19 12:52:36 2012 +0100
    Fix asm constraints in bn_add_words, bn_sub_words

diff --git a/crypto/bn/asm/x86_64-gcc.c b/crypto/bn/asm/x86_64-gcc.c
index d34d2dc..dfb7506 100644
--- a/crypto/bn/asm/x86_64-gcc.c
+++ b/crypto/bn/asm/x86_64-gcc.c
@@ -199,7 +199,7 @@ BN_ULONG bn_add_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 	"	lea	1(%2),%2	\n"
 	"	loop	1b		\n"
 	"	sbbq	%0,%0		\n"
-		: "=r"(ret),"+c"(n),"+r"(i)
+		: "=&r"(ret),"+c"(n),"+r"(i)
 		: "r"(rp),"r"(ap),"r"(bp)
 		: "cc"
 	);
@@ -224,7 +224,7 @@ BN_ULONG bn_sub_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 	"	lea	1(%2),%2	\n"
 	"	loop	1b		\n"
 	"	sbbq	%0,%0		\n"
-		: "=r"(ret),"+c"(n),"+r"(i)
+		: "=&r"(ret),"+c"(n),"+r"(i)
 		: "r"(rp),"r"(ap),"r"(bp)
 		: "cc"
 	);