linux-kernel - [PATCH 1/2] lib/mpi: avoid assembler warning

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Message-Id: <1456490794-1034544-1-git-send-email-arnd@arndb.de>
Date:	Fri, 26 Feb 2016 13:46:26 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	linux-crypto@...r.kernel.org, David Howells <dhowells@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] lib/mpi: avoid assembler warning

A wrapper around the umull assembly instruction might reuse
the input register as an output, which is undefined on
some ARM machines, as pointed out by this assembler warning:

  CC      lib/mpi/generic_mpih-mul1.o
/tmp/ccxJuxIy.s: Assembler messages:
/tmp/ccxJuxIy.s:53: rdhi, rdlo and rm must all be different
  CC      lib/mpi/generic_mpih-mul2.o
/tmp/ccI0scAD.s: Assembler messages:
/tmp/ccI0scAD.s:53: rdhi, rdlo and rm must all be different
  CC      lib/mpi/generic_mpih-mul3.o
/tmp/ccMvVQcp.s: Assembler messages:
/tmp/ccMvVQcp.s:53: rdhi, rdlo and rm must all be different

This changes the constraints to force different registers to
be used as output.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 lib/mpi/longlong.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
index b90e255c2a68..93336502af08 100644
--- a/lib/mpi/longlong.h
+++ b/lib/mpi/longlong.h
@@ -216,7 +216,7 @@ extern UDItype __udiv_qrnnd(UDItype *, UDItype, UDItype, UDItype);
 	__asm__ ("%@ Inlined umul_ppmm\n" \
 		"umull %r1, %r0, %r2, %r3" \
 	: "=&r" ((USItype)(xh)), \
-			"=r" ((USItype)(xl)) \
+			"=&r" ((USItype)(xl)) \
 	: "r" ((USItype)(a)), \
 			"r" ((USItype)(b)) \
 	: "r0", "r1")
-- 
2.7.0