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=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 EDE19C35242 for ; Fri, 14 Feb 2020 06:35:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CE7DB2187F for ; Fri, 14 Feb 2020 06:35:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728945AbgBNGfw convert rfc822-to-8bit (ORCPT ); Fri, 14 Feb 2020 01:35:52 -0500 Received: from mga09.intel.com ([134.134.136.24]:50157 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725990AbgBNGfv (ORCPT ); Fri, 14 Feb 2020 01:35:51 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Feb 2020 22:35:51 -0800 X-IronPort-AV: E=Sophos;i="5.70,439,1574150400"; d="scan'208";a="227499154" Received: from ablank-mobl.ger.corp.intel.com (HELO localhost) ([10.252.39.179]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Feb 2020 22:35:48 -0800 From: Jani Nikula To: Nathan Chancellor , Joonas Lahtinen , Rodrigo Vivi Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Nathan Chancellor , Michel =?utf-8?Q?D=C3=A4nzer?= , Chris Wilson Subject: Re: [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma In-Reply-To: <20200214054706.33870-1-natechancellor@gmail.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20200214054706.33870-1-natechancellor@gmail.com> Date: Fri, 14 Feb 2020 08:36:15 +0200 Message-ID: <87v9o965gg.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Feb 2020, Nathan Chancellor wrote: > A recent commit in clang added -Wtautological-compare to -Wall, which is > enabled for i915 after -Wtautological-compare is disabled for the rest > of the kernel so we see the following warning on x86_64: > > ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1433:22: warning: > result of comparison of constant 576460752303423487 with expression of > type 'unsigned int' is always false > [-Wtautological-constant-out-of-range-compare] > if (unlikely(remain > N_RELOC(ULONG_MAX))) > ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ > ../include/linux/compiler.h:78:42: note: expanded from macro 'unlikely' > # define unlikely(x) __builtin_expect(!!(x), 0) > ^ > 1 warning generated. > > It is not wrong in the case where ULONG_MAX > UINT_MAX but it does not > account for the case where this file is built for 32-bit x86, where > ULONG_MAX == UINT_MAX and this check is still relevant. > > Cast remain to unsigned long, which keeps the generated code the same > (verified with clang-11 on x86_64 and GCC 9.2.0 on x86 and x86_64) and > the warning is silenced so we can catch more potential issues in the > future. > > Link: https://github.com/ClangBuiltLinux/linux/issues/778 > Suggested-by: Michel Dänzer > Signed-off-by: Nathan Chancellor Works for me as a workaround, Reviewed-by: Jani Nikula > --- > > Round 3 :) > > Previous threads/patches: > > https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@gmail.com/ > https://lore.kernel.org/lkml/20200211050808.29463-1-natechancellor@gmail.com/ > > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > index 60c984e10c4a..47f4d8ab281e 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > @@ -1430,7 +1430,7 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct i915_vma *vma) > > urelocs = u64_to_user_ptr(entry->relocs_ptr); > remain = entry->relocation_count; > - if (unlikely(remain > N_RELOC(ULONG_MAX))) > + if (unlikely((unsigned long)remain > N_RELOC(ULONG_MAX))) > return -EINVAL; > > /* -- Jani Nikula, Intel Open Source Graphics Center