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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 A7FBFC352A4 for ; Tue, 11 Feb 2020 00:15:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C31B20715 for ; Tue, 11 Feb 2020 00:15:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KQylGPxd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727505AbgBKAPa (ORCPT ); Mon, 10 Feb 2020 19:15:30 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:45912 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727455AbgBKAPa (ORCPT ); Mon, 10 Feb 2020 19:15:30 -0500 Received: by mail-pf1-f193.google.com with SMTP id 2so4504937pfg.12; Mon, 10 Feb 2020 16:15:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=r5ohSbrtojTxCSFCkg8rYW9zCxgtMfpQZkLpXgHPTpk=; b=KQylGPxdiaGvk+7Y+4BneWCRdxmvASR00418Jv7gHTm/EZxZkAZt8Hj7qbRh3JOGFy oxl2x5m6yV6iMc5YLIlOjEox0c90qBOT+fwVam8DvtExHZ1JkoYBwPjGtqNhiRcZzwQq TtY0mLuruewCig3yfcTFRMCAesZI8xyGIGReVInSiRC1XvxvpQq6veSmY1sNTWCG4Fwl LLMc6e0KVLz+vy3Umv/5RTzT1ubEHIv95CCcWRKM8oKJcjqI1cX1Y8UcJSx9wMbYbBi7 H3aZXfZWPc9EK8I+72g6uwnDPYF0MUz4QJtn6UjV0uyHk3G1avz4AXDxhznkFQy9s/5o JNFg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=r5ohSbrtojTxCSFCkg8rYW9zCxgtMfpQZkLpXgHPTpk=; b=BWJkqB8kaXTQ6vRF2tfYkpBrwH5Aal6vL1eAr01oX1eJZmRWaMdlXeSb+bT5Wxq0ev lnD7SH0TK7edouZG0a82L94GS6l2gAz2Ls9shKGUmebYbR7m7jI+MTkaeidC9DY8wEpG pTiTkiBx9KioZ4HyKMvP9bNN7bEpqUhzP8XgsBjlqh/RC//rXTR5kmyy5lKSZZCqUIcK appJ9QczHPEmclmdmhUVhdF6Z7vAy7Wk/Pu7eH4x1Jh1xN3b0L8S2WP7ze8C5wUWVu87 jcxchbeZgZedXllDkuiwxdvOR86zNa8zoG/A+DqQnXwTI4a3FwFFz2yxM1HAq7Ghl+ZB fa7Q== X-Gm-Message-State: APjAAAWuyuIpZdTjeu2Lf6XZxEOFiZd6kCV23/J4MXkrVK1roLjQvTLf DYorImDf4/koNJ1Pv9bat+s= X-Google-Smtp-Source: APXvYqwaI1pmqbF0HQJmCdNPwqmI2s1WtrWOIQeTyY/IRieg6LQrDFvOhcDN4OionXTTqMh7Vs1K2g== X-Received: by 2002:a65:5549:: with SMTP id t9mr4124065pgr.439.1581380129926; Mon, 10 Feb 2020 16:15:29 -0800 (PST) Received: from ast-mbp ([2620:10d:c090:200::2:685c]) by smtp.gmail.com with ESMTPSA id z26sm1201161pgu.80.2020.02.10.16.15.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Feb 2020 16:15:29 -0800 (PST) Date: Mon, 10 Feb 2020 16:15:27 -0800 From: Alexei Starovoitov To: Palmer Dabbelt Cc: Bjorn Topel , daniel@iogearbox.net, ast@kernel.org, zlim.lnx@gmail.com, catalin.marinas@arm.com, will@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com, shuah@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, clang-built-linux@googlegroups.com, kernel-team@android.com Subject: Re: [PATCH 4/4] arm64: bpf: Elide some moves to a0 after calls Message-ID: <20200211001526.xbfwdnpjqrg3ed6q@ast-mbp> References: <20200128021145.36774-1-palmerdabbelt@google.com> <20200128021145.36774-5-palmerdabbelt@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200128021145.36774-5-palmerdabbelt@google.com> User-Agent: NeoMutt/20180223 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Jan 27, 2020 at 06:11:45PM -0800, Palmer Dabbelt wrote: > > + /* Handle BPF_REG_0, which may be in the wrong place because the ARM64 > + * ABI doesn't match the BPF ABI for function calls. */ > + if (ctx->reg0_in_reg1) { > + /* If we're writing BPF_REG_0 then we don't need to do any > + * extra work to get the registers back in their correct > + * locations. */ > + if (insn->dst_reg == BPF_REG_0) > + ctx->reg0_in_reg1 = false; > + > + /* If we're writing to BPF_REG_1 then we need to save BPF_REG_0 > + * into the correct location if it's still alive, as otherwise > + * it will be clobbered. */ > + if (insn->dst_reg == BPF_REG_1) { > + if (!dead_register(ctx, off + 1, BPF_REG_0)) > + emit(A64_MOV(1, A64_R(7), A64_R(0)), ctx); > + ctx->reg0_in_reg1 = false; > + } > + } I'm not sure this is correct, since it processes insns as a linear code, but there could be jumps in the middle. The logic should be following the control flow of the program. The verifier is a better place to do such analysis. I don't see how JITs can do it on their own.