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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D2F8CCA47B for ; Mon, 13 Jun 2022 11:33:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354521AbiFMLc6 (ORCPT ); Mon, 13 Jun 2022 07:32:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56244 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354247AbiFML3E (ORCPT ); Mon, 13 Jun 2022 07:29:04 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3852A3ED05; Mon, 13 Jun 2022 03:43:05 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id AD6146120F; Mon, 13 Jun 2022 10:43:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BAB89C34114; Mon, 13 Jun 2022 10:43:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655116984; bh=Xvs3Hif9Ug6sEW4GtZhKm3Ql8kmVD8B7BE1wcEUV/Fs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nOebNRsVgO0I871ScSKqblSmlQRgNHKrlSo5Y1X3N+rQOjm0Qu3QSWIQkPZo4XG/S ALtWTJKwohYq9COxkexPWyE6Ro+pnZKTVy5IsOqdZqOC9OT0Bawk05MqedaN6v0BMP EW3RLoQhWF+tputKPa62t5xawhCUEBCUPOBaxGmY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nick Desaulniers , Sean Christopherson , Paolo Bonzini Subject: [PATCH 5.4 248/411] Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug Date: Mon, 13 Jun 2022 12:08:41 +0200 Message-Id: <20220613094936.209985399@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220613094928.482772422@linuxfoundation.org> References: <20220613094928.482772422@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sean Christopherson commit 1aa0e8b144b6474c4914439d232d15bfe883636b upstream. Add a config option to guard (future) usage of asm_volatile_goto() that includes "tied outputs", i.e. "+" constraints that specify both an input and output parameter. clang-13 has a bug[1] that causes compilation of such inline asm to fail, and KVM wants to use a "+m" constraint to implement a uaccess form of CMPXCHG[2]. E.g. the test code fails with :1:29: error: invalid operand in inline asm: '.long (${1:l}) - .' int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; } ^ :1:29: error: unknown token in expression :1:9: note: instantiated into assembly here .long () - . ^ 2 errors generated. on clang-13, but passes on gcc (with appropriate asm goto support). The bug is fixed in clang-14, but won't be backported to clang-13 as the changes are too invasive/risky. gcc also had a similar bug[3], fixed in gcc-11, where gcc failed to account for its behavior of assigning two numbers to tied outputs (one for input, one for output) when evaluating symbolic references. [1] https://github.com/ClangBuiltLinux/linux/issues/1512 [2] https://lore.kernel.org/all/YfMruK8%2F1izZ2VHS@google.com [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98096 Suggested-by: Nick Desaulniers Reviewed-by: Nick Desaulniers Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20220202004945.2540433-2-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- init/Kconfig | 5 +++++ 1 file changed, 5 insertions(+) --- a/init/Kconfig +++ b/init/Kconfig @@ -33,6 +33,11 @@ config CC_CAN_LINK config CC_HAS_ASM_GOTO def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) +config CC_HAS_ASM_GOTO_TIED_OUTPUT + depends on CC_HAS_ASM_GOTO_OUTPUT + # Detect buggy gcc and clang, fixed in gcc-11 clang-14. + def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null) + config TOOLS_SUPPORT_RELR def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)