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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 2D22DC432C2 for ; Thu, 26 Sep 2019 07:47:36 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 00E1921A4A for ; Thu, 26 Sep 2019 07:47:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="DjZDLaIc" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00E1921A4A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=kGxtbYXLoOdJ2siez4QK9yNx7g9GpqJv2jVSuJtCYLw=; b=DjZDLaIc/QC4yw P7hEP1PbqP7qB0QfLcYV9WdJmObrRoCE2P3X+uUZM8VI66B4S6I7sny7JpWnDIt5tai/HU/Up9LiG qxek5zkDy3HCAXt9izQeZnIuIOjQmieU7uSKL5dykjM+4LyQPiyFODi8dbCg3EX3+OSqK5waS0kAA qwK07xWcm1evECof7QTRXlkyjzu7p/GS0glUhDKLbBts20OZPyZwR4FbD8ZtzqG8eWf9N5yF9ioON SVdfw2K2s9mORWDyJYOQzXrRaAMjIP4UzwL3SoFn+o5f7fb58pDUbw8WldMe357QDcaHq9jhDhqXw Rfeo84S1pbWyhO44qT8w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDOUs-0002sT-Tt; Thu, 26 Sep 2019 07:47:30 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDOUp-0002rk-Jy for linux-arm-kernel@lists.infradead.org; Thu, 26 Sep 2019 07:47:29 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8C81B1000; Thu, 26 Sep 2019 00:47:25 -0700 (PDT) Received: from iMac.local (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 80B8F3F836; Thu, 26 Sep 2019 00:47:24 -0700 (PDT) Date: Thu, 26 Sep 2019 08:47:18 +0100 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH] arm64: Allow disabling of the compat vDSO Message-ID: <20190926074717.GA26802@iMac.local> References: <20190925130926.50674-1-catalin.marinas@arm.com> <20190925170838.GK7042@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1 (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190926_004727_748363_E29DAC61 X-CRM114-Status: GOOD ( 28.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ard Biesheuvel , Nick Desaulniers , LKML , Thomas Gleixner , Will Deacon , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 26, 2019 at 01:06:50AM +0100, Vincenzo Frascino wrote: > On 9/25/19 6:08 PM, Catalin Marinas wrote: > > On Wed, Sep 25, 2019 at 09:53:16AM -0700, Nick Desaulniers wrote: > >> On Wed, Sep 25, 2019 at 6:09 AM Catalin Marinas wrote: > >>> Suggestions for future improvements of the compat vDSO handling: > >>> > >>> - replace the CROSS_COMPILE_COMPAT prefix with a full COMPATCC; maybe > >>> check that it indeed produces 32-bit code > > CROSS_COMPILE_COMPAT is called like this for symmetry with CROSS_COMPILE. Actually, what gets in the way is the CONFIG_CROSS_COMPILE_COMPAT_VDSO. We can keep CROSS_COMPILE_COMPAT together with COMPATCC initialised to $(CROSS_COMPILE_COMPAT)gcc. When we will be able to build the compat vDSO with clang, we just pass COMPATCC=clang on the make line and the kernel Makefile will figure out the --target option from CROSS_COMPILE_COMPAT (see how CLANG_FLAGS is handled). If we stick only to env variables or make cmd line (without Kconfig) for the compiler name, we can add a COMPATCC_IS_CLANG in the Kconfig directly and simply not allow the enabling the COMPAT_VDSO if we don't have the right compiler. This saves us warnings during build. > >>> - check whether COMPATCC is clang or not rather than CC_IS_CLANG, which > >>> only checks the native compiler > >> > >> When cross compiling, IIUC CC_IS_CLANG is referring to CC which is the > >> cross compiler, which is different than HOSTCC which is the host > >> compiler. HOSTCC is used mostly for things in scripts/ while CC is > >> used to compile a majority of the kernel in a cross compile. > > > > We need the third compiler here for the compat vDSO (at least with gcc), > > COMPATCC. I'm tempted to just drop the CONFIG_CROSS_COMPILE_COMPAT_VDSO > > altogether and only rely on a COMPATCC. This way we can add > > COMPATCC_IS_CLANG etc. in the Kconfig checks directly. > > > > If clang can build both 32 and 64-bit with the same binary (just > > different options), we could maybe have COMPATCC default to CC and add a > > check on whether COMPATCC generates 32-bit binaries. > > clang requires the --target option for specifying the 32bit triple. > Basically $(TRIPLE)-gcc is equivalent to gcc --target $(TRIPLE). > We need a configuration option to encode this. Since we don't have a CONFIG_* option for the cross-compiler prefix, we shouldn't have one for the compat compiler either. If you want to build the compat vDSO with clang, just pass COMPATCC=clang together with CROSS_COMPILE_COMPAT. We can add Kconfig checks to actually verify that COMPATCC generates 32-bit binaries (e.g. COMPATCC_CAN_LINK32). > >>> - clean up the headers includes; vDSO should not include kernel-only > >>> headers that may even contain code patched at run-time > >> > >> This is a big one; Clang validates the inline asm constraints for > >> extended inline assembly, GCC does not for dead code. So Clang chokes > >> on the inclusion of arm64 headers using extended inline assembly when > >> being compiled for arm-linux-gnueabi. > > > > Whether clang or gcc, I'd like this fixed anyway. At some point we may > > inadvertently rely on some code which is patched at boot time for the > > kernel code but not for the vDSO. > > Do we have any code of this kind in header files? > > The vDSO library uses only a subset of the headers (mainly Macros) hence all the > unused symbols should be compiled out. Is your concern only theoretical or do > you have an example on where this could be happening? At the moment it's rather theoretical. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel