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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 5620DC433E7 for ; Wed, 2 Sep 2020 09:33:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31E462072A for ; Wed, 2 Sep 2020 09:33:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HjsMqkRL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726167AbgIBJdR (ORCPT ); Wed, 2 Sep 2020 05:33:17 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53292 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726140AbgIBJdP (ORCPT ); Wed, 2 Sep 2020 05:33:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1599039193; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=B0quNSFWJydVcjT4g12GaFKmwRp9vjC6YdaNQQrBLao=; b=HjsMqkRLKSAi0JNstdX952pkB7nHvhuDqk8CL4rjgBYyWNYEYsZZTOrAqcwNk4DL8uD7Ze IJIPb46rC80QxVP6xYFgKvTtWeVORaWzb1scBMLdxjyHQ24QALeXoph5vAsIrJXeVkiJrb Yqnck+BvsvpUp4jj4XDhno+g+21fwJE= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-316-g1qULsj2NK-KJ1KdQmCFDg-1; Wed, 02 Sep 2020 05:33:11 -0400 X-MC-Unique: g1qULsj2NK-KJ1KdQmCFDg-1 Received: by mail-wr1-f70.google.com with SMTP id n15so1730973wrv.23 for ; Wed, 02 Sep 2020 02:33:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=B0quNSFWJydVcjT4g12GaFKmwRp9vjC6YdaNQQrBLao=; b=L51CP9vzyycn8f5cNyPE8wGlU0KKufmaLPbaEmRMGcbHLb6oMrSERSobQtE8Purw4v aoLT8fHQDxIQanRCVYAQRq52AqprevwM5H8OsoeicM75+vKgglGbztDFwWRchuwP6OzX RMT3hKVgxlJhAFMLGyBj/Q4rChi8we/9IiOCHhaLhLCnnTldwsdSe6njQJpSRX+0A/9H PYtfGU120osebb/Hd6QIVP8G34zdabwFnZ944z2m2e7FvnoArGhm5kmehJe0VM8cK8B5 Tp1ZoslCgetttEZbtgvegagnIRNP0y3ahuT0WTOtotb1nCs6LBqBUwJ5qnQqFriyB4gl hCAQ== X-Gm-Message-State: AOAM5300F25F4wpdIm+8lJNBVq84d+vBhm+t6jV6GMVdTFGw8jexztiI PL1xEVsoIIui5LDVeRZl+5F2+o4qkR3puuVUaWIKj9l6siVBLI0s59H36H7eyl+5Pcj3eo68ZQh 0+i43DrjSf4l9 X-Received: by 2002:a05:6000:36d:: with SMTP id f13mr5973782wrf.425.1599039190672; Wed, 02 Sep 2020 02:33:10 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz8y1aebYfshZwxYRaVDE/wXWKmOBIgQjHtdLL96N6qWlZ4DNjYuP2cUeG8MGqG7X7FLqI7oQ== X-Received: by 2002:a05:6000:36d:: with SMTP id f13mr5973770wrf.425.1599039190456; Wed, 02 Sep 2020 02:33:10 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id k8sm5876626wma.16.2020.09.02.02.33.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2020 02:33:09 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 49B3118200B; Wed, 2 Sep 2020 11:33:09 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Yonghong Song , Andrii Nakryiko Cc: bpf , Alexei Starovoitov , Daniel Borkmann , Kernel Team , John Fastabend , Jesper Dangaard Brouer Subject: Re: [PATCH bpf-next 1/2] bpf: fix a verifier failure with xor In-Reply-To: <465da51a-793e-5ea0-85dc-56ab4f36ae34@fb.com> References: <20200825064608.2017878-1-yhs@fb.com> <20200825064608.2017937-1-yhs@fb.com> <465da51a-793e-5ea0-85dc-56ab4f36ae34@fb.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 02 Sep 2020 11:33:09 +0200 Message-ID: <87d034ikve.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Yonghong Song writes: > On 9/1/20 1:07 PM, Andrii Nakryiko wrote: >> On Mon, Aug 24, 2020 at 11:47 PM Yonghong Song wrote: >>> >>> bpf selftest test_progs/test_sk_assign failed with llvm 11 and llvm 12. >>> Compared to llvm 10, llvm 11 and 12 generates xor instruction which >> >> Does this mean that some perfectly working BPF programs will now fail >> to verify on older kernels, if compiled with llvm 11 or llvm 12? If > > Right. > >> yes, is there something that one can do to prevent Clang from using >> xor in such situations? > > The xor is generated by the combination of llvm simplifyCFG and > instrCombine phase. > > The following is a hack to prevent compiler from generating xor's. Wait, so this means that we can no longer tell people to just use the newest LLVM version - now we have to keep track of a minimum *and* maximum LLVM version for each kernel version? Could we maybe try to not *keep* making it harder for people to use BPF? :/ As for the patch, sure, make the verifier smarter, but I also feel like LLVM should be fixed to not suddenly emit such xor instructions... -Toke