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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9D69DC4727E for ; Wed, 23 Sep 2020 14:49:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 65AA6206FB for ; Wed, 23 Sep 2020 14:49:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726631AbgIWOtZ (ORCPT ); Wed, 23 Sep 2020 10:49:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726572AbgIWOtZ (ORCPT ); Wed, 23 Sep 2020 10:49:25 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA320C0613CE; Wed, 23 Sep 2020 07:49:24 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL657-004bBq-D5; Wed, 23 Sep 2020 14:49:17 +0000 Date: Wed, 23 Sep 2020 15:49:17 +0100 From: Al Viro To: David Laight Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" , Linus Torvalds Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-ID: <20200923144917.GM3421308@ZenIV.linux.org.uk> References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Sep 23, 2020 at 02:38:24PM +0000, David Laight wrote: > From: Al Viro > > Sent: 23 September 2020 15:17 > > > > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > > + unsigned long nr_segs, unsigned long fast_segs, > > > > Hmm... For fast_segs unsigned long had always been ridiculous > > (4G struct iovec on caller stack frame?), but that got me wondering about > > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > > > The thing is, import_iovec() takes unsigned int there. Which is fine > > (hell, the maximal value that can be accepted in 1024), except that > > we do pass unsigned long syscall argument to it in some places. > > It will make diddly-squit difference. > The parameters end up in registers on most calling conventions. > Plausibly you get an extra 'REX' byte on x86 for the 64bit value. > What you want to avoid is explicit sign/zero extension and value > masking after arithmetic. Don't tell me what I want; your telepathic abilities are consistently sucky. I am *NOT* talking about microoptimization here. I have described the behaviour change of syscall caused by commit 5 years ago. Which is generally considered a problem. Then I asked whether that behaviour change would fall under the "if nobody noticed, it's not a userland ABI breakage" exception. Could you show me the point where I have expressed concerns about the quality of amd64 code generated for that thing, before or after the change in question? From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Date: Wed, 23 Sep 2020 14:49:17 +0000 Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-Id: <20200923144917.GM3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> In-Reply-To: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> To: David Laight Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" , Linus Torvalds On Wed, Sep 23, 2020 at 02:38:24PM +0000, David Laight wrote: > From: Al Viro > > Sent: 23 September 2020 15:17 > > > > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > > + unsigned long nr_segs, unsigned long fast_segs, > > > > Hmm... For fast_segs unsigned long had always been ridiculous > > (4G struct iovec on caller stack frame?), but that got me wondering about > > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > > > The thing is, import_iovec() takes unsigned int there. Which is fine > > (hell, the maximal value that can be accepted in 1024), except that > > we do pass unsigned long syscall argument to it in some places. > > It will make diddly-squit difference. > The parameters end up in registers on most calling conventions. > Plausibly you get an extra 'REX' byte on x86 for the 64bit value. > What you want to avoid is explicit sign/zero extension and value > masking after arithmetic. Don't tell me what I want; your telepathic abilities are consistently sucky. I am *NOT* talking about microoptimization here. I have described the behaviour change of syscall caused by commit 5 years ago. Which is generally considered a problem. Then I asked whether that behaviour change would fall under the "if nobody noticed, it's not a userland ABI breakage" exception. Could you show me the point where I have expressed concerns about the quality of amd64 code generated for that thing, before or after the change in question? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726572AbgIWOtZ (ORCPT ); Wed, 23 Sep 2020 10:49:25 -0400 Date: Wed, 23 Sep 2020 15:49:17 +0100 From: Al Viro Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-ID: <20200923144917.GM3421308@ZenIV.linux.org.uk> References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> Sender: Al Viro List-ID: To: David Laight Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" , Linus Torvalds On Wed, Sep 23, 2020 at 02:38:24PM +0000, David Laight wrote: > From: Al Viro > > Sent: 23 September 2020 15:17 > > > > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > > + unsigned long nr_segs, unsigned long fast_segs, > > > > Hmm... For fast_segs unsigned long had always been ridiculous > > (4G struct iovec on caller stack frame?), but that got me wondering about > > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > > > The thing is, import_iovec() takes unsigned int there. Which is fine > > (hell, the maximal value that can be accepted in 1024), except that > > we do pass unsigned long syscall argument to it in some places. > > It will make diddly-squit difference. > The parameters end up in registers on most calling conventions. > Plausibly you get an extra 'REX' byte on x86 for the 64bit value. > What you want to avoid is explicit sign/zero extension and value > masking after arithmetic. Don't tell me what I want; your telepathic abilities are consistently sucky. I am *NOT* talking about microoptimization here. I have described the behaviour change of syscall caused by commit 5 years ago. Which is generally considered a problem. Then I asked whether that behaviour change would fall under the "if nobody noticed, it's not a userland ABI breakage" exception. Could you show me the point where I have expressed concerns about the quality of amd64 code generated for that thing, before or after the change in question? 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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5C23AC2D0A8 for ; Wed, 23 Sep 2020 14:57:22 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 83139206D9 for ; Wed, 23 Sep 2020 14:57:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83139206D9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BxLqy4kqSzDqNt for ; Thu, 24 Sep 2020 00:57:18 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=ftp.linux.org.uk (client-ip=2002:c35c:fd02::1; helo=zeniv.linux.org.uk; envelope-from=viro@ftp.linux.org.uk; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BxLg30tQTzDqHY for ; Thu, 24 Sep 2020 00:49:27 +1000 (AEST) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL657-004bBq-D5; Wed, 23 Sep 2020 14:49:17 +0000 Date: Wed, 23 Sep 2020 15:49:17 +0100 From: Al Viro To: David Laight Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-ID: <20200923144917.GM3421308@ZenIV.linux.org.uk> References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-aio@kvack.org" , "linux-mips@vger.kernel.org" , David Howells , "linux-mm@kvack.org" , "keyrings@vger.kernel.org" , "sparclinux@vger.kernel.org" , Christoph Hellwig , "linux-arch@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-scsi@vger.kernel.org" , Linus Torvalds , Arnd Bergmann , "linux-block@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Jens Axboe , "linux-parisc@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Sep 23, 2020 at 02:38:24PM +0000, David Laight wrote: > From: Al Viro > > Sent: 23 September 2020 15:17 > > > > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > > + unsigned long nr_segs, unsigned long fast_segs, > > > > Hmm... For fast_segs unsigned long had always been ridiculous > > (4G struct iovec on caller stack frame?), but that got me wondering about > > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > > > The thing is, import_iovec() takes unsigned int there. Which is fine > > (hell, the maximal value that can be accepted in 1024), except that > > we do pass unsigned long syscall argument to it in some places. > > It will make diddly-squit difference. > The parameters end up in registers on most calling conventions. > Plausibly you get an extra 'REX' byte on x86 for the 64bit value. > What you want to avoid is explicit sign/zero extension and value > masking after arithmetic. Don't tell me what I want; your telepathic abilities are consistently sucky. I am *NOT* talking about microoptimization here. I have described the behaviour change of syscall caused by commit 5 years ago. Which is generally considered a problem. Then I asked whether that behaviour change would fall under the "if nobody noticed, it's not a userland ABI breakage" exception. Could you show me the point where I have expressed concerns about the quality of amd64 code generated for that thing, before or after the change in question? 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=-5.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 0EF87C4727F for ; Wed, 23 Sep 2020 14:51:05 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 A4F142223E for ; Wed, 23 Sep 2020 14:51:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="WzLsVIe9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A4F142223E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.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=7esn22J0jeN3huhB7vpvG2bGt6mOUw9DcDE35i/+UTk=; b=WzLsVIe930vsyGgCjl+v376p2 vxmUARl3HBz8xTrEWofIeBqkVZ6Y2w2DuxtMl69dop3jzewCRCK0Xkr3zNR9uveQLINle4E56w0iG sieo3ndL5DPeCIrf+JULv4khiwWpQlmMM1YWHGhdZpynm4D/neXpeHY8s4AtvXNQ9JSGMdxUbUw2J vb9gKeAc+oGkBHKDE1jC20qZsrpGSU5hPBxeoBtA92wc0tfJ4bQzPXjQ/QlKjTdbruY+lye2BEkKl w2gesPywWHjG7He9F8C7lpytC08r3Oz3qMFqyIJsJvz+gwx3kllLxqkx/WTTYjArZMIxlNSKnmwaW J56bzTgZQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL65G-00055w-OZ; Wed, 23 Sep 2020 14:49:26 +0000 Received: from [2002:c35c:fd02::1] (helo=ZenIV.linux.org.uk) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL65C-00055Z-Q7 for linux-arm-kernel@lists.infradead.org; Wed, 23 Sep 2020 14:49:24 +0000 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL657-004bBq-D5; Wed, 23 Sep 2020 14:49:17 +0000 Date: Wed, 23 Sep 2020 15:49:17 +0100 From: Al Viro To: David Laight Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-ID: <20200923144917.GM3421308@ZenIV.linux.org.uk> References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200923_104922_870627_0555056A X-CRM114-Status: GOOD ( 20.82 ) 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: "linux-aio@kvack.org" , "linux-mips@vger.kernel.org" , David Howells , "linux-mm@kvack.org" , "keyrings@vger.kernel.org" , "sparclinux@vger.kernel.org" , Christoph Hellwig , "linux-arch@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-scsi@vger.kernel.org" , Linus Torvalds , Arnd Bergmann , "linux-block@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Jens Axboe , "linux-parisc@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Sep 23, 2020 at 02:38:24PM +0000, David Laight wrote: > From: Al Viro > > Sent: 23 September 2020 15:17 > > > > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > > + unsigned long nr_segs, unsigned long fast_segs, > > > > Hmm... For fast_segs unsigned long had always been ridiculous > > (4G struct iovec on caller stack frame?), but that got me wondering about > > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > > > The thing is, import_iovec() takes unsigned int there. Which is fine > > (hell, the maximal value that can be accepted in 1024), except that > > we do pass unsigned long syscall argument to it in some places. > > It will make diddly-squit difference. > The parameters end up in registers on most calling conventions. > Plausibly you get an extra 'REX' byte on x86 for the 64bit value. > What you want to avoid is explicit sign/zero extension and value > masking after arithmetic. Don't tell me what I want; your telepathic abilities are consistently sucky. I am *NOT* talking about microoptimization here. I have described the behaviour change of syscall caused by commit 5 years ago. Which is generally considered a problem. Then I asked whether that behaviour change would fall under the "if nobody noticed, it's not a userland ABI breakage" exception. Could you show me the point where I have expressed concerns about the quality of amd64 code generated for that thing, before or after the change in question? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel