From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755549AbdDERjk (ORCPT ); Wed, 5 Apr 2017 13:39:40 -0400 Received: from mail-it0-f45.google.com ([209.85.214.45]:35005 "EHLO mail-it0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752510AbdDERit (ORCPT ); Wed, 5 Apr 2017 13:38:49 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170405165603.87264-1-mka@chromium.org> From: Ard Biesheuvel Date: Wed, 5 Apr 2017 18:38:47 +0100 Message-ID: Subject: Re: [PATCH] crypto: arm64/sha: use %c constraint code in ASM_EXPORT To: Robin Murphy Cc: Matthias Kaehlcke , Herbert Xu , Grant Grundler , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Greg Hackmann , Michael Davidson , "linux-crypto@vger.kernel.org" , "David S . Miller" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5 April 2017 at 18:21, Robin Murphy wrote: > On 05/04/17 18:08, Ard Biesheuvel wrote: >> Hoi Matthias! >> >> On 5 April 2017 at 17:56, Matthias Kaehlcke wrote: >>> From: Greg Hackmann >>> >>> The current definition of ASM_EXPORT doesn't work properly with clang, >>> according to https://bugs.llvm.org//show_bug.cgi?id=27250#c3 it relies on >>> gcc specific behavior. Change the constraint from an intermediate to an >>> output expression which works with both gcc and clang. >>> >>> From: Greg Hackmann >>> Commit-message-by: Matthias Kaehlcke >>> Signed-off-by: Greg Hackmann >>> Signed-off-by: Matthias Kaehlcke >>> --- >>> arch/arm64/crypto/sha1-ce-glue.c | 2 +- >>> arch/arm64/crypto/sha2-ce-glue.c | 2 +- >>> 2 files changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c >>> index aefda9868627..c71e94ba0e43 100644 >>> --- a/arch/arm64/crypto/sha1-ce-glue.c >>> +++ b/arch/arm64/crypto/sha1-ce-glue.c >>> @@ -18,7 +18,7 @@ >>> #include >>> >>> #define ASM_EXPORT(sym, val) \ >>> - asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val)); >>> + asm(".globl " #sym "; .set " #sym ", %c0" :: "I"(val)); >>> >>> MODULE_DESCRIPTION("SHA1 secure hash using ARMv8 Crypto Extensions"); >>> MODULE_AUTHOR("Ard Biesheuvel "); >>> diff --git a/arch/arm64/crypto/sha2-ce-glue.c b/arch/arm64/crypto/sha2-ce-glue.c >>> index 7cd587564a41..381b5fb2dcb2 100644 >>> --- a/arch/arm64/crypto/sha2-ce-glue.c >>> +++ b/arch/arm64/crypto/sha2-ce-glue.c >>> @@ -18,7 +18,7 @@ >>> #include >>> >>> #define ASM_EXPORT(sym, val) \ >>> - asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val)); >>> + asm(".globl " #sym "; .set " #sym ", %c0" :: "I"(val)); >>> >>> MODULE_DESCRIPTION("SHA-224/SHA-256 secure hash using ARMv8 Crypto Extensions"); >>> MODULE_AUTHOR("Ard Biesheuvel "); >> >> I am fine with this change, although I would really like to add a >> better reference to the commit log. It is *very* difficult to find any >> documentation regarding non-trivial uses of inline asm constraints, >> and if %c0 is the correct syntax, surely we can quote something better >> than a LLVM bugzilla entry? Also, where does the distinction between >> 'intermediate' vs 'output' expression come from? > > FWIW, GCC docs do say (under the helpfully-obvious "x86 operand > modifiers" section[1]): > > c Require a constant operand and print the constant > expression with no punctuation. > > Which more or less makes sense in this this context too. As an aside, > though, since this is emitting a general integer argument to an > assembler directive, and not an operand to an ADD instruction, how come > we're using "I" and not "i" as the constraint in the first place? > No reason. "I" came to mind when writing the code, and worked as expected. Perhaps we should just fix that at the same time.