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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 2B8D5C433E0 for ; Tue, 2 Jun 2020 12:09:17 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 08713205CB for ; Tue, 2 Jun 2020 12:09:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08713205CB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jg5jA-0005cM-H2; Tue, 02 Jun 2020 12:09:08 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jg5j9-0005cH-1k for xen-devel@lists.xenproject.org; Tue, 02 Jun 2020 12:09:07 +0000 X-Inumbo-ID: db1ece96-a4c9-11ea-9947-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id db1ece96-a4c9-11ea-9947-bc764e2007e4; Tue, 02 Jun 2020 12:09:06 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id DCCD5AE2C; Tue, 2 Jun 2020 12:09:07 +0000 (UTC) Subject: Re: [PATCH v2 03/14] x86/shstk: Introduce Supervisor Shadow Stack support To: Andrew Cooper References: <20200527191847.17207-1-andrew.cooper3@citrix.com> <20200527191847.17207-4-andrew.cooper3@citrix.com> <4f535d4c-b3b3-fe5b-8b57-af736dc0a360@suse.com> <20200529155118.GL2105@perard.uk.xensource.com> <4c759ccc-b256-c074-0bd8-fe2d5c728715@citrix.com> From: Jan Beulich Message-ID: <2f22aac8-6fb0-95a0-3c2f-47c4379b87dc@suse.com> Date: Tue, 2 Jun 2020 14:09:04 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: <4c759ccc-b256-c074-0bd8-fe2d5c728715@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Anthony PERARD , Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 29.05.2020 20:39, Andrew Cooper wrote: > On 29/05/2020 16:51, Anthony PERARD wrote: >> On Fri, May 29, 2020 at 01:59:55PM +0200, Jan Beulich wrote: >>> On 28.05.2020 20:10, Andrew Cooper wrote: >>>> On 28/05/2020 11:25, Jan Beulich wrote: >>>>> On 27.05.2020 21:18, Andrew Cooper wrote: >>>>>> --- a/xen/scripts/Kconfig.include >>>>>> +++ b/xen/scripts/Kconfig.include >>>>>> @@ -31,6 +31,10 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -E -x c /dev/null -o /de >>>>>> # Return y if the linker supports , n otherwise >>>>>> ld-option = $(success,$(LD) -v $(1)) >>>>>> >>>>>> +# $(as-instr,) >>>>>> +# Return y if the assembler supports , n otherwise >>>>>> +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -) >>>>> Is this actually checking the right thing in the clang case? >>>> Appears to work correctly for me.  (Again, its either fine, or need >>>> bugfixing anyway for 4.14, and raising with Linux as this is unmodified >>>> upstream code like the rest of Kconfig.include). >>> This answer made me try it out: On a system with clang 5 and >>> binutils 2.32 "incsspd %eax" translates fine with >>> -no-integrated-as but doesn't without. The previously mentioned >>> odd use of CLANG_FLAGS, perhaps together with the disconnect >>> from where we establish whether to use -no-integrated-as in the >>> first place (arch.mk; I have no idea whether the CFLAGS >>> determined would be usable by the kconfig invocation, nor how >>> to solve the chicken-and-egg problem there if this is meant to >>> work that way), may be the reason for this. Cc-ing Anthony once >>> again ... >> I've just prepare/sent a patch which should fix this CLANG_FLAGS issue >> and allows to tests the assembler in Kconfig. >> >> See: [XEN PATCH] xen/build: introduce CLANG_FLAGS for testing other CFLAGS > > Thanks.  I've checked carefully, and this is an improvement from before. > > Therefore I have acked and included the patch. > > However, I think there is a further problem.  When -no-integrated-as > does get passed down, I don't see Clang falling back to using the Gnu > assember, so I suspect we have a further plumbing problem.  (It only > affects Clang 5.0 and earlier, so obsolete toolchains these days). Hmm, what exactly do you mean saying "I don't see Clang falling back ..."? In the playing I did, I specifically passed -v to see what gets or does not get invoked, and it was /usr/bin/as that did get used (clang 5.0.1). Obviously it'll be whatever /usr/bin/as is then. Jan