From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EA0AC43331 for ; Sun, 29 Mar 2020 18:02:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 67CAA20714 for ; Sun, 29 Mar 2020 18:02:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=agner.ch header.i=@agner.ch header.b="C/RqPRCX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728319AbgC2SCn (ORCPT ); Sun, 29 Mar 2020 14:02:43 -0400 Received: from mail.kmu-office.ch ([178.209.48.109]:33778 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727485AbgC2SCm (ORCPT ); Sun, 29 Mar 2020 14:02:42 -0400 Received: from webmail.kmu-office.ch (unknown [IPv6:2a02:418:6a02::a3]) by mail.kmu-office.ch (Postfix) with ESMTPSA id 1322D5C4E62; Sun, 29 Mar 2020 20:02:40 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=agner.ch; s=dkim; t=1585504960; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=b9KjmaInreQ1tydeO4+d2Tu0zpyS1eiXjbaSxIllgiU=; b=C/RqPRCXjLhWk84XCkxEpAz6C6eU8DoWZh5HF/QbiE6W8nT6MBPglT9ScEq3JaK3lLMdmn OYd1TygqS5m+8smVmpFAHoHcE0Rsc6DLUzTyvL4vNAwFF1Q2oC8Mv3jUhHZN5ob+r/SlyJ ECL4k0WAP4ORh9Na8akRL7LN8oix/o0= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Sun, 29 Mar 2020 20:02:40 +0200 From: Stefan Agner To: Nick Desaulniers Cc: Russell King , Arnd Bergmann , Masahiro Yamada , Manoj Gupta , Jian Cai , Linux ARM , LKML , clang-built-linux Subject: Re: [PATCH] ARM: warn if pre-UAL assembler syntax is used In-Reply-To: References: User-Agent: Roundcube Webmail/1.4.1 Message-ID: X-Sender: stefan@agner.ch Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-03-17 08:55, Stefan Agner wrote: > On 2020-03-17 01:00, Nick Desaulniers wrote: >> Revert "ARM: 8846/1: warn if divided syntax assembler is used"On Thu, >> Feb 27, 2020 at 4:19 PM Stefan Agner wrote: >>> >>> Remove the -mno-warn-deprecated assembler flag for GCC versions newer >>> than 5.1 to make sure the GNU assembler warns in case non-unified >>> syntax is used. >> >> Hi Stefan, sorry for the late reply from me; digging out my backlog. >> Do you happen to have a godbolt link perhaps that demonstrates this? >> It sounds like GCC itself is emitting pre-UAL? > > Yes, that is what Russell observed and caused the revert: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b752bb405a13 > > I do not have a godbolt link at hand, I just built the complete kernel > using some GCC toolchains I had locally available and noticed that the > problem persists up to and including GCC 5.0. I did not track down what > exactly is causing GCC to emit pre-UAL. Godbolt link: https://godbolt.org/z/fxYq_s However, the warning does not appear on godbolt.org, presumably because the compiler is started such that it does not invoke the assembler (at least that is what I understand when using -v). However, on my end this leads to: $ arm-linux-gnueabihf-gcc -marm -march=armv7-a -O2 -c test.c -o test --save-temps test.s: Assembler messages: test.s:33: Warning: conditional infixes are deprecated in unified syntax $ arm-linux-gnueabihf-gcc --version arm-linux-gnueabihf-gcc (Linaro GCC 4.9-2016.02) 4.9.4 20151028 (prerelease) And line 33 contains a non-unified assembler mnemonic: strneb r2, [r3] Note: I do have to explicitly use .syntax unified. It seems that gcc is not explicitly doing this, but if any inline assembly is changing the assembler mode (e.g. what including arch/arm/include/asm/unified.h is doing) then the assembler warnings start to appear. -- Stefan > >> >>> >>> This also prevents a warning when building with Clang and enabling >>> its integrated assembler: >>> clang-10: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,' >>> >>> This is a second attempt of commit e8c24bbda7d5 ("ARM: 8846/1: warn if >>> divided syntax assembler is used"). >> >> Would it be helpful to also make note of >> commit b752bb405a13 ("Revert "ARM: 8846/1: warn if divided syntax >> assembler is used"")? > > Sure, I can do that. > >> >> >>> >>> Signed-off-by: Stefan Agner >>> --- >>> arch/arm/Makefile | 14 +++++++++----- >>> 1 file changed, 9 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/arm/Makefile b/arch/arm/Makefile >>> index db857d07114f..a6c8c9f39185 100644 >>> --- a/arch/arm/Makefile >>> +++ b/arch/arm/Makefile >>> @@ -119,21 +119,25 @@ ifeq ($(CONFIG_CC_IS_CLANG),y) >>> CFLAGS_ABI += -meabi gnu >>> endif >>> >>> -# Accept old syntax despite ".syntax unified" >>> -AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W) >> >> This existing code is quite bad for Clang, which doesn't support >> `-Wa,-mno-warn-deprecated`, so this falls back to `-Wa,-W`, which >> disables all warnings from the assembler, which we definitely do not >> want. That alone is worth putting in the GCC guard. But I would like >> more info about GCC above before signing off. > > FWIW, I submitted this to the patch tracker already, but I don't think > it got merged already. > > -- > Stefan > >> >>> - >>> ifeq ($(CONFIG_THUMB2_KERNEL),y) >>> -CFLAGS_ISA :=-mthumb -Wa,-mimplicit-it=always $(AFLAGS_NOWARN) >>> +CFLAGS_ISA :=-mthumb -Wa,-mimplicit-it=always >>> AFLAGS_ISA :=$(CFLAGS_ISA) -Wa$(comma)-mthumb >>> # Work around buggy relocation from gas if requested: >>> ifeq ($(CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11),y) >>> KBUILD_CFLAGS_MODULE +=-fno-optimize-sibling-calls >>> endif >>> else >>> -CFLAGS_ISA :=$(call cc-option,-marm,) $(AFLAGS_NOWARN) >>> +CFLAGS_ISA :=$(call cc-option,-marm,) >>> AFLAGS_ISA :=$(CFLAGS_ISA) >>> endif >>> >>> +ifeq ($(CONFIG_CC_IS_GCC),y) >>> +ifeq ($(call cc-ifversion, -lt, 0501, y), y) >>> +# GCC <5.1 emits pre-UAL code and causes assembler warnings, suppress them >>> +CFLAGS_ISA +=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W) >>> +endif >>> +endif >>> + >>> # Need -Uarm for gcc < 3.x >>> KBUILD_CFLAGS +=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm >>> KBUILD_AFLAGS +=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float >>> --